Defining surrogate serologic tests with respect to predicting protective vaccine efficacy: poliovirus vaccination

Safety and immunogenicity of shorter interval schedules of the novel oral poliovirus vaccine type 2 in infants: a phase 3, randomised, controlled, non-inferiority study in the Dominican Republic

BACKGROUND

The novel oral poliovirus vaccine type 2 (nOPV2) is now authorised by a WHO emergency use listing and widely distributed to interrupt outbreaks of circulating vaccine-derived poliovirus type 2. As protection of vulnerable populations, particularly young infants, could be facilitated by shorter intervals between the two recommended doses, we aimed to assess safety and non-inferiority of immunogenicity of nOPV2 in 1-week, 2-week, and 4-week schedules.

METHODS

In this phase 3, open-label, randomised trial, healthy, full-term, infants aged 6-8 weeks from a hospital or a clinic in the Dominican Republic were randomly allocated (1:1:1 ratio) using a pre-prepared, computer-generated randomisation schedule to three groups to receive two doses of nOPV2 immunisations with a 1-week interval (group A), 2-week interval (group B), or 4-week interval (group C). The nOPV2 vaccine was given at a 0·1 mL dose and contained at least 105 50% cell culture infective dose. Neutralising antibodies against poliovirus types 1, 2, and 3 were measured before each immunisation and 4 weeks after the second dose. The primary outcome was the type 2 seroconversion rate 28 days after the second dose, and the non-inferiority margin was defined as a lower bound 95% CI of greater than -10%. Safety and reactogenicity were assessed through diary cards completed by the parent or guardian. The trial is registered with ClinicalTrials.gov, NCT05033561.

FINDINGS

We enrolled 905 infants between Dec 16, 2021, and March 28, 2022. 872 infants were included in the per-protocol analyses: 289 in group A, 293 in group B, and 290 in group C. Type 2 seroconversion rates were 87·5% (95% CI 83·2 to 91·1) in group A (253 of 289 participants), 91·8% (88·1 to 94·7) in group B (269 of 293 participants), and 95·5% (92·5 to 97·6) in group C (277 of 290 participants). Non-inferiority was shown for group B compared with group C (difference in rates -3·7; 95% CI -7·9 to 0·3), but not for group A compared with group C (-8·0; -12·7 to -3·6). 4 weeks after the second nOPV2 dose, type 2 neutralising antibodies increased in all three groups such that over 95% of each group was seroprotected against polio type 2, although final geometric mean titres tended to be highest with longer intervals between doses. Immunisation with nOPV2 was well tolerated with no causal association to vaccination of any severe or serious adverse event; one death from septic shock during the study was unrelated to the vaccine.

INTERPRETATION

Two nOPV2 doses administered 1 week or 2 weeks apart from age 6 weeks to 8 weeks were safe and immunogenic. Immune responses after a 2-week interval were non-inferior to those after the standard 4-week interval, but marked responses after a 1-week interval suggest that schedules with an over 1-week interval can be used to provide flexibility to campaigns to improve coverage and hasten protection during circulating vaccine-derived poliovirus type 2 outbreaks.

FUNDING

Bill & Melinda Gates Foundation.

Use of Inactivated Polio Vaccine Among U.S. Adults: Updated Recommendations of the Advisory Committee on Immunization Practices - United States, 2023

Poliovirus can cause poliomyelitis and lifelong paralysis. Although wild poliovirus types 2 and 3 have been eradicated, wild poliovirus type 1 and vaccine-derived polioviruses are still circulating in multiple countries worldwide. In 2022, a case of paralytic polio caused by vaccine-derived poliovirus type 2 was identified in an unvaccinated young adult in New York. This case and subsequent detection of community transmission underscored the ongoing risk for importation of poliovirus into the United States and risk for poliomyelitis among unvaccinated persons. However, previous Advisory Committee on Immunization Practices (ACIP) recommendations for adult polio vaccination were limited to adults known to be at increased risk for exposure. During October 2022-June 2023, the ACIP Polio Vaccine Work Group reviewed data on poliovirus surveillance and epidemiology, safety and effectiveness of inactivated poliovirus vaccine (IPV), and other considerations outlined in the ACIP Evidence to Recommendations Framework. On June 21, 2023, ACIP voted to recommend that all U.S. adults aged ≥18 years who are known or suspected to be unvaccinated or incompletely vaccinated against polio complete a primary polio vaccination series with IPV. This report summarizes evidence considered for this recommendation and provides clinical guidance for the use of IPV in adults.

Antigenic diversity of type 1 polioviruses and its implications for the efficacy of polio vaccines

Inactivated Polio Vaccines (IPV) and live Oral Polio Vaccine (OPV) were introduced in the mid-20th century, and their coordinated worldwide use led to almost complete elimination of the disease, with only one serotype of poliovirus remaining endemic in just two countries. Polio eradication will lead to discontinuation of OPV use and its replacement with IPV or other vaccines that are currently under development that will need to be tested in clinical trials. Despite decades of research, questions remain about the serological correlates of polio vaccine efficacy, specifically whether the vaccines are equally protective against immunologically different strains of the same serotype. The absence of significant morbidity does not allow use of a protection endpoint in clinical trials, so the answer could be obtained only by using surrogate markers such as immunogenicity. In this study, a panel of wild and vaccine-derived polioviruses of serotype 1 were tested in neutralization assays with sera from vaccine-immunized individuals. The results demonstrated that there was a significant difference in titers of neutralizing antibodies in human sera when measured against different strains. When measured with a homologous strain used for vaccine manufacture all subjects had detectable levels of antibodies, while neutralization tests with some heterologous strains failed to detect neutralizing antibodies in a number of subjects. Administration of a booster dose of IPV led to a significant increase in neutralizing titers against all strains. Results of the experiments using animal sera, performed to obtain more information on protectivity of neutralizing antibodies against heterologous strains, were consistent with the results obtained in the assays using human sera. These results are discussed in the context of serological biomarkers of protection against poliomyelitis, suggesting that potency of vaccines made from serologically different strains should be determined against both homologous and heterologous challenge viruses.

Co-administration of Oral Cholera Vaccine With Oral Polio Vaccine Among Bangladeshi Young Children: A Randomized Controlled Open Label Trial to Assess Interference

BACKGROUND

Cholera remains a public health threat for low- and middle-income countries, particularly in Asia and Africa. Shanchol™, an inactivated oral cholera vaccine (OCV) is currently in use globally. OCV and oral poliovirus vaccines (OPV) could be administered concomitantly, but the immunogenicity and safety of coadministration among children aged 1-3 years is unknown.

METHODS

We undertook an open-label, randomized, controlled, inequality trial in Dhaka city, Bangladesh. Healthy children aged 1-3 years were randomly assigned to 1 of 3 groups: bivalent OPV (bOPV)-alone, OCV-alone, or combined bOPV + OCV and received vaccines on the day of enrollment and 28 days later. Blood samples were collected on the day of enrollment, day 28, and day 56. Serum poliovirus neutralizing antibodies and vibriocidal antibodies against Vibrio cholerae O1 were assessed using microneutralization assays.

RESULTS

A total of 579 children aged 1‒3 years were recruited, 193 children per group. More than 90% of the children completed visits at day 56. Few adverse events following immunization were recorded and were equivalent among study arms. On day 28, 60% (90% confidence interval: 53%-67%) and 54% (46%-61%) of participants with co-administration of bOPV + OCV responded to polioviruses type 1 and 3, respectively, compared to 55% (47%-62%) and 46% (38%-53%) in the bOPV-only group. Additionally, >50% of participants showed a ≥4-fold increase in vibriocidal antibody titer responses on day 28, comparable to the responses observed in OCV-only arm.

CONCLUSIONS

Co-administration of bOPV and OCV is safe and effective in children aged 1-3 years and can be cost-beneficial.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov (NCT03581734).

Achieving high immunogenicity against poliovirus with fractional doses of inactivated poliovirus vaccine in Ecuador-results from a cross-sectional serological survey

Background

In January 2018, Ecuador changed its routine immunization schedule by replacing one full dose of inactivated poliovirus vaccine (IPV) administered intramuscularly at 2 months of age with two doses of fractional IPV (1/5th of full dose, fIPV) administered intradermally at 2 and 4 months of age; and bivalent oral poliovirus vaccine (serotypes 1 and 3, bOPV) continues to be used. We compared seroprevalence and titres of polio antibodies achieved by the past and the current immunization schedules.

Methods

This was a cross-sectional serological survey in children in Ecuador who received bOPV and either one IPV dose in 2017 or two fIPV doses in 2018. One blood sample was collected between October 2020 and March 2021 and analysed for presence of poliovirus neutralizing antibodies at CDC, Atlanta by microneutralization assay.

Findings

We obtained 321 analysable samples from 329 (97·6%) enrolled children (160 received IPV and 161 fIPV). For serotype 2, seroprevalence was 50·0% (CI95%= 44·2-55·8%) for IPV and 83·2% (CI95%=78·5-87·1%) for fIPV recipients (p<0·001). Median antibody titers for serotype 2 were significantly lower for IPV than for fIPV recipients (3·0, CI95%= 3 – 3·5 vs. 4·8, CI95%= 4·5 – 5·2, p<0·001). Seroprevalence for serotypes 1 and 3 was above 90% and was not significantly different between IPV and fIPV recipients.

Interpretation

Ecuador achieved significantly better poliovirus serotype 2 immunogenicity with two fIPV doses than with one IPV dose, while preserving vaccine supply and reducing costs. Our data provide further evidence that fIPV is a beneficial and potentially a cost-effective option in polio immunization.

Funding

WHO obtained funds for the study from Rotary International.

Review of use of inactivated poliovirus vaccine in campaigns to control type 2 circulating vaccine derived poliovirus (cVDPV) outbreaks

Delivering inactivated poliovirus vaccine (IPV) with oral poliovirus vaccine (OPV) in campaigns has been explored to accelerate the control of type 2 circulating vaccine-derived poliovirus (cVDPV) outbreaks. A review of scientific literature suggests that among populations with high prevalence of OPV failure, a booster with IPV after at least two doses of OPV may close remaining humoral and mucosal immunity gaps more effectively than an additional dose of trivalent OPV. However, IPV alone demonstrates minimal advantage on humoral immunity compared with monovalent and bivalent OPV, and cannot provide the intestinal immunity that prevents infection and spread to those individuals not previously exposed to live poliovirus of the same serotype (i.e. type 2 for children born after the switch from trivalent to bivalent OPV in April 2016). A review of operational data from polio campaigns shows that addition of IPV increases the cost and logistic complexity of campaigns. As a result, campaigns in response to an outbreak often target small areas. Large campaigns require a delay to ensure logistics are in place for IPV delivery, and may need implementation in phases that last several weeks. Challenges to delivery of injectable vaccines through house-to-house visits also increases the risk of missing the children who are more likely to benefit from IPV: those with difficult access to routine immunization and other health services. Based upon this information, the Strategic Advisory Group of Experts in immunization (SAGE) recommended in October 2020 the following strategies: provision of a second dose of IPV in routine immunization to reduce the risk and number of paralytic cases in countries at risk of importation or new emergences; and use of type 2 OPV in high-quality campaigns to interrupt transmission and avoid seeding new type 2 cVDPV outbreaks.

Safety and immunogenicity of inactivated poliovirus vaccine schedules for the post-eradication era: a randomised open-label, multicentre, phase 3, non-inferiority trial

BACKGROUND

Following the global eradication of wild poliovirus, countries using live attenuated oral poliovirus vaccines will transition to exclusive use of inactivated poliovirus vaccine (IPV) or fractional doses of IPV (f-IPV; a f-IPV dose is one-fifth of a normal IPV dose), but IPV supply and cost constraints will necessitate dose-sparing strategies. We compared immunisation schedules of f-IPV and IPV to inform the choice of optimal post-eradication schedule.

METHODS

This randomised open-label, multicentre, phase 3, non-inferiority trial was done at two centres in Panama and one in the Dominican Republic. Eligible participants were healthy 6-week-old infants with no signs of febrile illness or known allergy to vaccine components. Infants were randomly assigned (1:1:1:1, 1:1:1:2, 2:1:1:1), using computer-generated blocks of four or five until the groups were full, to one of four groups and received: two doses of intradermal f-IPV (administered at 14 and 36 weeks; two f-IPV group); or three doses of intradermal f-IPV (administered at 10, 14, and 36 weeks; three f-IPV group); or two doses of intramuscular IPV (administered at 14 and 36 weeks; two IPV group); or three doses of intramuscular IPV (administered at 10, 14, and 36 weeks; three IPV group). The primary outcome was seroconversion rates based on neutralising antibodies for poliovirus type 1 and type 2 at baseline and at 40 weeks (4 weeks after the second or third vaccinations) in the per-protocol population to allow non-inferiority and eventually superiority comparisons between vaccines and regimens. Three co-primary outcomes concerning poliovirus types 1 and 2 were to determine if seroconversion rates at 40 weeks of age after a two-dose regimen (administered at weeks 14 and 36) of intradermally administered f-IPV were non-inferior to a corresponding two-dose regimen of intramuscular IPV; if seroconversion rates at 40 weeks of age after a two-dose IPV regimen (weeks 14 and 36) were non-inferior to those after a three-dose IPV regimen (weeks 10, 14, and 36); and if seroconversion rates after a two-dose f-IPV regimen (weeks 14 and 36) were non-inferior to those after a three-dose f-IPV regimen (weeks 10, 14, and 36). The non-inferiority boundary was set at -10% for the lower bound of the two-sided 95% CI for the seroconversion rate difference.. Safety was assessed as serious adverse events and important medical events. This study is registered on ClinicalTrials.gov, NCT03239496.

FINDINGS

From Oct 23, 2017, to Nov 13, 2018, we enrolled 773 infants (372 [48%] girls) in Panama and the Dominican Republic (two f-IPV group n=217, three f-IPV group n=178, two IPV group n=178, and three IPV group n=200). 686 infants received all scheduled vaccine doses and were included in the per-protocol analysis. We observed non-inferiority for poliovirus type 1 seroconversion rate at 40 weeks for the two f-IPV dose schedule (95·9% [95% CI 92·0-98·2]) versus the two IPV dose schedule (98·7% [95·4-99·8]), and for the three f-IPV dose schedule (98·8% [95·6-99·8]) versus the three IPV dose schedule (100% [97·9-100]). Similarly, poliovirus type 2 seroconversion rate at 40 weeks for the two f-IPV dose schedule (97·9% [94·8-99·4]) versus the two IPV dose schedule (99·4% [96·4-100]), and for the three f-IPV dose schedule (100% [97·7-100]) versus the three IPV dose schedule (100% [97·9-100]) were non-inferior. Seroconversion rate for the two f-IPV regimen was statistically superior 4 weeks after the last vaccine dose in the 14 and 36 week schedule (95·9% [92·0-98·2]) compared with the 10 and 14 week schedule (83·2% [76·5-88·6]; p=0·0062) for poliovirus type 1. Statistical superiority of the 14 and 36 week schedule was also found for poliovirus type 2 (14 and 36 week schedule 97·9% [94·8-99·4] vs 10 and 14 week schedule 83·9% [77·2-89·2]; p=0·0062), and poliovirus type 3 (14 and 36 week schedule 84·5% [78·7-89·3] vs 10 and 14 week schedule 73·3% [65·8-79·9]; p=0·0062). For IPV, a two dose regimen administered at 14 and 36 weeks (99·4% [96·4-100]) was superior a 10 and 14 week schedule (88·9% [83·4-93·1]; p<0·0001) for poliovirus type 2, but not for type 1 (14 and 36 week schedule 98·7% [95·4-99·8] vs 10 and 14 week schedule 95·6% [91·4-98·1]), or type 3 (14 and 36 week schedule 97·4% [93·5-99·3] vs 10 and 14 week schedule 93·9% [89·3-96·9]). There were no related serious adverse events or important medical events reported in any group showing safety was unaffected by administration route or schedule.

INTERPRETATION

Our observations suggest that adequate immunity against poliovirus type 1 and type 2 is provided by two doses of either IPV or f-IPV at 14 and 36 weeks of age, and broad immunity is provided with three doses of f-IPV, enabling substantial savings in cost and supply. These novel clinical data will inform global polio immunisation policy for the post-eradication era.

FUNDING

Bill & Melinda Gates Foundation.

Immune Priming and Long-term Persistence of Memory B Cells After Inactivated Poliovirus Vaccine in Macaque Models: Support for at least 2 Doses

Background

As a risk-mitigation strategy to minimize paralytic polio following withdrawal of Sabin type 2 from the oral poliovirus vaccine in April 2016, a single full dose or 2 fractional doses of inactivated poliovirus vaccine (IPV) are recommended. However, limited knowledge exists on long-term persistence of immune memory following 1- or 2-dose IPV schedules.

Methods

We examined induction and maintenance of immune memory following single- vs 2-dose IPV schedules, either full-dose intramuscular or fractional-dose intradermal, in rhesus macaques. Humoral responses, bone marrow–homing antibody-secreting plasma cells, and blood-circulating/lymph node–homing memory B cells were examined longitudinally.

Results

A single dose of IPV, either full or fractional, induced binding antibodies and memory B cells in all vaccinated macaques, despite failing to induce neutralizing antibodies (NT Abs) in many of them. However, these memory B cells declined rapidly, reaching below detection in the systemic circulation by 5 months; although a low frequency of memory B cells was detectable in draining lymph nodes of some, but not all, animals. By contrast, a 2-dose vaccination schedule, either full or fractional, efficiently induced NT Abs in all animals along with bone marrow–homing plasma cells and memory B cells. These memory B cells persisted in the systemic circulation for up to 16 months, the maximum duration tested after the second dose of vaccination.

Conclusions

Two doses of IPV, regardless of whether fractional or full, are more effective than a single dose for inducing long-lasting memory B cells.

Immunogenicity of a combined schedule of trivalent oral and inactivated polio vaccines in South African infants

Background: South Africa transitioned from using live-attenuated trivalent oral polio vaccine (tOPV), to a combination of tOPV and inactivated polio vaccine (IPV) in April 2009. We evaluated the immunogenicity of the South African combined tOPV-IPV schedule versus the tOPV-only schedule in South African infants. Methods: Serum samples of HIV-unexposed infants were analysed retrospectively from two cohorts; infants enrolled from April 2005 through June 2006 and infants enrolled from December 2009 to April 2010. The primary vaccination series of the tOPV-only schedule included doses at birth, 6, 10 and 14 weeks, and the tOPV-IPV schedule included tOPV at birth and 6 weeks and IPV at 6, 10 and 14 weeks. Serum polio neutralising antibody titres to serotype-1, serotype-2 and serotype-3 were evaluated in infants at 18 weeks of age. Results: Infants who received the tOPV-IPV schedule had higher GMTs than infants who received tOPV-only for serotype-2 (9.63 vs. 8.80, P < 0.001) and serotype-3 (10.01 vs. 8.53, P < 0.001), as well as higher sero-protective titres for serotype-1 (100% vs. 96%, P = 0.014). Conclusion: Our data support the option of the South African combined polio vaccination schedule as an immunogenic option for a combined schedule.

Assessment of seroprevalence against poliovirus among Italian adolescents and adults

In 2002, the WHO European Region was declared polio-free. Nonetheless global eradication has not yet been completed and the reintroduction from at risk areas is still possible. This seroprevalence study evaluated samples collected from each Italian region in the 12−50 years old age range to assess protection against Poliovirus (PV) 1, 2 and 3 among subjects immunised with different vaccination schedules. 1073 samples (50.5% females) were examined. WHO standardized microneutralization assay was used. Seroprotection rates were 92.9%, 96.2% and 83.4%, for PV1, PV2 and PV3, respectively. Geometric Mean Titres (GMTs) were higher for PV2 (52.8) and PV1 (41.1) than for PV3 (21.0). Increasing the age, a decreasing trend in seropositivity was observed, in particular for PV3. The 2017–2019 Italian National Immunisation Plan emphasises, as primary objective, the maintenance of the polio-free status and strongly validates the 2 + 1 schedule in the first year of life with IPV vaccine associated with the administration of booster doses at 6 years and during the adolescence. Surveillance system and high population immunity are crucial to ensure the maintenance of polio-free status.

Low Rates of Poliovirus Antibodies in Primary Immunodeficiency Patients on Regular Intravenous Immunoglobulin Treatment

PURPOSE

Poliovirus has been nearly eliminated as part of a world-wide effort to immunize and contain circulating wild-type polio. Nevertheless, poliovirus has been detected in water supplies and represents a threat to patients with humoral immunodeficiencies where infection can be fatal. To define the risk, we analyzed antibodies to poliovirus 1, 2, and 3 in serum samples collected over a year from patients with primary immunodeficiency diseases (PID) on regular intravenous immunoglobulin (IVIG) replacement.

METHODS

Twenty-one patients on regular IVIG replacement therapy were evaluated: Twelve patients with common variable immune deficiency (CVID), six with X-linked agammaglobulinemia (XLA), and three with hyper IgM syndrome (HIGM). Over 1 year, four blood samples were collected from each of these patients immediately before immunoglobulin infusion. One sample of IVIG administered to each patient in the month before blood collection was also evaluated. Poliovirus antibodies were quantified by seroneutralization assay.

RESULTS

All IVIG samples had detectable antibodies to the three poliovirus serotypes. Despite that, only 52.4, 61.9, and 19.0% of patients showed protective antibody titers for poliovirus 1, 2, and 3, respectively. Only two patients (9.5%) had protective antibodies for the three poliovirus serotypes on all samples. Most patients were therefore susceptible to all three poliovirus serotypes.

CONCLUSIONS

This study demonstrates the need for ongoing vigilance regarding exposure of patients with PID to poliovirus in the community.

Is Italian population protected from Poliovirus? Results of a seroprevalence survey in Florence, Italy

Objectives: Periodical assessments of population susceptibility to polioviruses (PV) is essential for evaluating population protection and planning appropriate vaccination strategies. The aim of the current work was to assess serological protective titers against all three polioviruses in the general population of Florence. Methods: A convenience sample of 328 sera, collected in 2009 in Florence (Central Italy) was analyzed. Samples were considered protective if neutralizing antibodies were detected at dilutions ≥1:8, according to the WHO protocols. Results: The immune coverage was 75.3%, 69.2% and 46% for PV1, PV2 and PV3, respectively. The protective titers of neutralizing antibodies were generally higher in children up to 14 years of age, with 74.4% (PV1), 75.6% (PV2) and 56.7% (PV3) of seroprevalence. From the age of 11 years, most of the study subjects were seronegative for PV3. Conclusions: In a polio-free country with strong migration pressures, such as Italy, our results bring clear support to the recent recommendation of Italian health authorities to introduce a fifth dose of IPV vaccine in adolescence all over the country.

Intradermal Administration of Fractional Doses of Inactivated Poliovirus Vaccine: A Dose-Sparing Option for Polio Immunization

A fractional dose of inactivated poliovirus vaccine (fIPV) administered by the intradermal route delivers one fifth of the full vaccine dose administered by the intramuscular route and offers a potential dose-sparing strategy to stretch the limited global IPV supply while further improving population immunity. Multiple studies have assessed immunogenicity of intradermal fIPV compared with the full intramuscular dose and demonstrated encouraging results. Novel intradermal devices, including intradermal adapters and disposable-syringe jet injectors, have also been developed and evaluated as alternatives to traditional Bacillus Calmette-Guérin needles and syringes for the administration of fIPV. Initial experience in India, Pakistan, and Sri Lanka suggests that it is operationally feasible to implement fIPV vaccination on a large scale. Given the available scientific data and operational feasibility shown in early-adopter countries, countries are encouraged to consider introducing a fIPV strategy into their routine immunization and supplementary immunization activities.

Needle adapters for intradermal administration of fractional dose of inactivated poliovirus vaccine: Evaluation of immunogenicity and programmatic feasibility in Pakistan

Administration of 1/5th dose of Inactivated poliovirus vaccine intradermally (fIPV) provides similar immune response as full-dose intramuscular IPV, however, fIPV administration with BCG needle and syringe (BCG NS) is technically difficult. We compared immune response after one fIPV dose administered with BCG NS to administration with intradermal devices, referred to as Device A and B; and assessed feasibility of conducting a door-to-door vaccination campaign with fIPV. In Phase I, 452 children 6-12months old from Karachi were randomized to receive one fIPV dose either with BCG NS, Device A or Device B in a health facility. Immune response was defined as seroconversion or fourfold rise in polio neutralizing antibody titer 28days after fIPV among children whose baseline titer ≤362. In Phase II, fIPV was administered during one-day door-to-door campaign to assess programmatic feasibility by evaluating vaccinators' experience. For all three poliovirus (PV) serotypes, the immune response after BCG NS and Device A was similar, however it was lower with Device B (34/44 (77%), 31/45 (69%), 16/30 (53%) respectively for PV1; 53/78 (68%), 61/83 (74%), 42/80 (53%) for PV2; and; 58/76 (76%), 56/80 (70%), 43/77 (56%) for PV3; p<0.05 for all three serotypes). Vaccinators reported problems filling Device B in both Phases; no other operational challenges were reported during Phase II. Use of fIPV offers a dose-saving alternative to full-dose IPV.

Low-dose Thimerosal in pediatric vaccines: Adverse effects in perspective

Vaccines are prophylactics used as the first line of intervention to prevent, control and eradicate infectious diseases. Young children (before the age of six months) are the demographic group most exposed to recommended/mandatory vaccines preserved with Thimerosal and its metabolite ethylmercury (EtHg). Particularly in the less-developed countries, newborns, neonates, and young children are exposed to EtHg because it is still in several of their pediatric vaccines and mothers are often immunized with Thimerosal-containing vaccines (TCVs) during pregnancy. While the immunogenic component of the product has undergone more rigorous testing, Thimerosal, known to have neurotoxic effects even at low doses, has not been scrutinized for the limit of tolerance alone or in combination with adjuvant-Al during immaturity or developmental periods (pregnant women, newborns, infants, and young children). Scientific evidence has shown the potential hazards of Thimerosal in experiments that modeled vaccine-EtHg concentrations. Observational population studies have revealed uncertainties related to neurological effects. However, consistently, they showed a link of EtHg with risk of certain neurodevelopment disorders, such as tic disorder, while clearly revealing the benefits of removing Thimerosal from children's vaccines (associated with immunological reactions) in developed countries. So far, only rich countries have benefited from withdrawing the risk of exposing young children to EtHg. Regarding Thimerosal administered to the very young, we have sufficient studies that characterize a state of uncertainty: the collective evidence strongly suggests that Thimerosal exposure is associated with adverse neurodevelopmental outcomes. It is claimed that the continued use of Thimerosal in the less-developed countries is due to the cost to change to another preservative, such as 2-phenoxyethanol. However, the estimated cost increase per child in the first year of life is lower than estimated lifetime cost of caring for a child with a neurodevelopmental disorder, such tic disorder. The evidence indicates that Thimerosal-free vaccine options should be made available in developing countries.

Achieving high seroprevalence against polioviruses in Sri Lanka--results from a serological survey, 2014

The immunization program in Sri Lanka consistently reaches >90% coverage with oral poliovirus vaccines (OPV), and no polio supplementary vaccination campaigns have been conducted since 2003. We evaluated serological protection against polioviruses in children. A cross-sectional community-based survey was performed in three districts of Sri Lanka (Colombo, Badulla, and Killinochi). Randomly selected children in four age groups (9–11 months, 3–4 years, 7–9 years, and 15 years) were tested for poliovirus neutralizing antibodies. All 400 enrolled children completed the study. The proportion of seropositive children for poliovirus Type 1 and Type 2 was >95% for all age groups; for poliovirus Type 3 it was 95%, 90%, 77%, and 75% in the respective age groups. The vaccination coverage in our sample based on vaccination cards or parental recall was >90% in all age groups. Most Sri Lankan children are serologically protected against polioviruses through routine immunization only. This seroprevalence survey provided baseline data prior to the anticipated addition of inactivated poliovirus vaccine (IPV) into the Sri Lankan immunization program and the switch from trivalent OPV (tOPV) to bivalent OPV (bOPV).

Monovalent type-1 oral poliovirus vaccine given at short intervals in Pakistan: a randomised controlled, four-arm, open-label, non-inferiority trial

BACKGROUND

Supplementary immunisation activities with oral poliovirus vaccines (OPVs) are usually separated by 4 week intervals; however, shorter intervals have been used in security-compromised areas and for rapid outbreak responses. We assessed the immunogenicity of monovalent type-1 oral poliovirus vaccine (mOPV1) given at shorter than usual intervals in Karachi, Pakistan.

METHODS

This was a multicentre, randomised, controlled, four-arm, open-label, non-inferiority trial done at five primary health-care centres in low-income communities in and around Karachi, Pakistan. Eligible participants were healthy newborn babies with a birthweight of at least 2·5 kg, for whom informed consent was provided by their parent or guardian, and lived less than 30 km from the study clinic. After receiving a birth dose of trivalent OPV, we enrolled and randomly assigned newborn babies (1:1:1:1) to receive two doses of mOPV1 with an interval of 1 week (mOPV1-1 week), 2 weeks (mOPV1-2 weeks), or 4 weeks (mOPV1-4 weeks) between doses, or two doses of bivalent OPV (bOPV) with an interval of 4 weeks between doses (bOPV-4 weeks). We gave the first study dose of OPV at age 6 weeks. We did the randomisation with a centrally generated, computerised allocation sequence with blocks of 16; participants' families and study physicians could not feasibly be masked to the allocations. Trial participants were excluded from local supplementary immunisation activities during the study period. The primary outcome was non-inferiority (within a 20% margin) between groups in seroconversion to type-1 poliovirus. The primary and safety analyses were done in the per-protocol population of infants who received all three doses of vaccine. This trial is registered with ClinicalTrials.gov, number NCT01586572, and is closed to new participants.

FINDINGS

Between March 1, 2012, and May 31, 2013, we enrolled 1009 newborn babies, and randomly assigned 829 (82%) to treatment. 554 (67%) of the 829 babies were included in the per-protocol analysis. Proportions of seroconversion to type-1 poliovirus were 107/135 (79%, 95% CI 72·4-86·1) with mOPV1-1 week, 108/135 (80%, 73·2-86·8) with mOPV1-2 weeks, 129/148 (87%, 80·9-92·0) with mOPV1-4 weeks, and 107/136 (79%, 71·8-85·6) with bOPV-4 weeks. Non-inferiority was shown between groups and no significant differences were noted. Ten participants died during the trial. Seven of these deaths occurred during the lead-in period before randomisation (two from diarrhoea, five from unknown causes). Three infants died from sepsis after random assignment. No deaths were attributed to the procedures or vaccines. Additionally, we noted no events of vaccine-associated paralysis.

INTERPRETATION

We identified no significant differences in responses to mOPV1 given with shorter intervals between doses than with the standard 4 week intervals. The short-interval strategy could be particularly beneficial when temporary windows of opportunity for safe access can be granted in areas of conflict--eg, during cease-fire periods. In such situations, we recommend shortening the interval between OPV doses to 7 days.

FUNDING

World Health Organization.

Diphtheria, tetanus and poliovirus antibody persistence 5 years after vaccination of pre-schoolers with two different diphtheria, tetanus and inactivated poliomyelitis vaccines (Td-IPV or DT-IPV) and immune responses to a booster dose of DTaP-IPV

INTRODUCTION

This follow-up study assessed the 5-year persistence of vaccine-induced antibodies (Td-IPV or DT-IPV) and the immune response to a booster dose of DTaP-IPV.

METHODS

This was an open-label, parallel-group (two arms), multicentre trial performed at 44 study sites in France. Children aged 11-13 years, of either sex, who received Td-IPV (Revaxis(®)) and DT-IPV (DT Polio(®)) vaccines at 6 years of age in one previous open-label trial with no further vaccination against diphtheria, tetanus, pertussis or poliomyelitis, were enrolled. All participants received a single intramuscular booster dose (0.5mL) of DTaP-IPV vaccine (Tetravac-Acellulaire(®)). Study endpoints were based on antibody persistence and post-booster immune responses. Safety was monitored throughout the study. Descriptive statistics were used for all analyses.

RESULTS

Of the 758 children included in the previous study, 274 were included in this follow-up study; 129 had previously been vaccinated with Td-IPV, and 145 had previously received DT-IPV. At least 96.5% of participants in both groups presented an anti-diphtheria and anti-tetanus concentration ≥0.01IU/mL, and anti-poliovirus types 1-3 titres≥8 (1/dilution). Following vaccination with DTaP-IPV, anti-diphtheria and anti-tetanus antibody concentrations ≥0.1IU/mL and anti-poliovirus types 1-3 antibody titres ≥8 (1/dilution) were achieved in all participants. DTaP-IPV was well tolerated in this study. There were no serious adverse events during the study, and no participant withdrew because of adverse events.

DISCUSSION

The present study confirmed the long-term immunity conferred by Td-IPV when given as a booster dose, and supports the use of Td-IPV as a second booster at 6 years of age in children previously vaccinated against diphtheria, tetanus and poliomyelitis types 1-3.

Immunogenicity of poliovirus vaccines in chronically malnourished infants: a randomized controlled trial in Pakistan

Reaching high population immunity against polioviruses (PV) is essential to achieving global polio eradication. Efficacy of oral poliovirus vaccine (OPV) varies and is lower among children living in tropical areas with impoverished environments. Malnutrition found as a risk factor for lower serological protection against PV. We compared whether inactivated polio vaccine (IPV) can be used to rapidly close the immunity gap among chronically malnourished (stunted) infants in Pakistan who will not be eligible for the 14 week IPV dose in routine EPI schedule. A phase 3, multicenter 4-arm randomized controlled trial conducted at five Primary Health Care (PHC) centers in Karachi, Pakistan. Infants, 9–12 months were stratified by length for age Z score into chronically malnourished and normally nourished. Infants were randomized to receive one dose of either bivalent OPV (bOPV) alone or bOPV + IPV. Baseline seroprevalence of PV antibodies and serum immune response to study vaccine dose were assessed by neutralization assay. Vaccine PV shedding in stool was evaluated 7 days after a bOPV challenge dose. Sera and stool were analyzed from 852/928 (92%) enrolled children. At baseline, the seroprevalence was 85.6% (n = 386), 73.6% (n = 332), and 70.7% (n = 319) in malnourished children against PV types 1, 2 and 3 respectively; and 94.1% (n = 448), 87.0% (n = 441) and 83.6% (n = 397) in the normally nourished group (p < 0.05). Children had previously received 9–10 doses of bOPV (80%) or tOPV (20%). One dose of IPV + bOPV given to malnourished children increased their serological protection (PV1, n = 201, 97.6%; PV2, n = 198, 96.1% and PV3, n = 189, 91.7%) to parity with normally nourished children who had not received IPV (p = <0.001). Seroconversion and boosting for all three serotypes was significantly more frequent in children who received IPV + bOPV than in those with bOPV only (p < 0.001) in both strata. Shedding of polioviruses in stool did not differ between study groups and ranged from 2.4% (n = 5) to 7.1% (n = 15). In malnourished children the shedding was reduced after bOPV + IPV compared to bOPV only.

Chronically malnourished infants were more likely to be unprotected against polioviruses than normal infants. bOPV + IPV helped close the immunity gap better than bOPV alone.

Polio vaccination: past, present and future

Live attenuated oral polio vaccine (OPV) and inactivated polio vaccine (IPV) are the tools being used to achieve eradication of wild polio virus. Because OPV can rarely cause paralysis and generate revertant polio strains, IPV will have to replace OPV after eradication of wild polio virus is certified to sustain eradication of all polioviruses. However, uncertainties remain related to IPV's ability to induce intestinal immunity in populations where fecal-oral transmission is predominant. Although substantial effectiveness and safety data exist on the use and delivery of OPV and IPV, several new research initiatives are currently underway to fill specific knowledge gaps to inform future vaccination policies that would assure polio is eradicated and eradication is maintained.

Polio endgame: the global introduction of inactivated polio vaccine

In 2013, the World Health Assembly endorsed a plan that calls for the ultimate withdrawal of oral polio vaccines (OPV) from all immunization programs globally. The withdrawal would begin in a phased manner with removal of the type 2 component of OPV in 2016 through a global switch from trivalent OPV to bivalent OPV (containing only types 1 and 3). To mitigate risks associated with immunity gaps after OPV type 2 withdrawal, the WHO Strategic Advisory Group of Experts has recommended that all 126 OPV-only using countries introduce at least one dose of inactivated polio vaccine into routine immunization programs by end-2015, before the trivalent OPV-bivalent OPV switch. The introduction of inactivated polio vaccine would reduce risks of reintroduction of type 2 poliovirus by providing some level of seroprotection, facilitating interruption of transmission if outbreaks occur, and accelerating eradication by boosting immunity to types 1 and 3 polioviruses.

Cross-sectional serologic assessment of immunity to poliovirus infection in high-risk areas of northern India

INTRODUCTION

The objectives of this survey were to assess the seroprevalence of antibodies to poliovirus types 1 and 3 and the impact of bivalent (types 1 and 3) oral poliovirus vaccine (bOPV) use in immunization campaigns in northern India.

METHODS

In August 2010, a 2-stage stratified cluster sampling method identified infants aged 6-7 months in high-risk blocks for wild poliovirus infection. Vaccination history, weight and length, and serum were collected to test for neutralizing antibodies to poliovirus types 1, 2, and 3.

RESULTS

Seroprevalences of antibodies to poliovirus types 1, 2, and 3 were 98% (95% confidence interval [CI], 97%-99%), 66% (95% CI, 62%-69%), and 77% (95% CI, 75%-79%), respectively, among 664 infants from Bihar and 616 infants from Uttar Pradesh. Infants had received a median of 3 bOPV doses and 2 monovalent type 1 OPV (mOPV1) doses through campaigns and 3 trivalent OPV (tOPV) doses through routine immunization. Among subjects with 0 tOPV doses, the seroprevalences of antibodies to type 3 were 50%, 77%, and 82% after 2, 3, and 4 bOPV doses, respectively. In multivariable analysis, malnutrition was associated with a lower seroprevalence of type 3 antibodies.

CONCLUSIONS

This study confirmed that replacing mOPV1 with bOPV in campaigns was successful in maintaining very high population immunity to type 1 poliovirus and substantially decreasing the immunity gap to type 3 poliovirus.

Immune responses after fractional doses of inactivated poliovirus vaccine using newly developed intradermal jet injectors: a randomized controlled trial in Cuba

INTRODUCTION

The World Health Organization recommends that, as part of the new polio endgame, a dose of inactivated poliovirus vaccine (IPV) be introduced by the end of 2015 in all countries using only oral poliovirus vaccine (OPV). Administration of fractional dose (1/5th of full dose) IPV (fIPV) intradermally may reduce costs, but its administration is cumbersome with BCG needle and syringe. We evaluated performance of two newly developed intradermal-only jet injectors and compared the immune response induced by fIPV with that induced by full-dose IPV.

METHODS

Children between 12 and 20 months of age, who had previously received two doses of OPV, were enrolled in Camaguey, Cuba. Subjects received a single dose of IPV (either full-dose IPV intramuscularly with needle and syringe or fIPV intradermally administered with one of two new injectors or with BCG needle or a conventional needle-free injector). Serum was tested for presence of poliovirus neutralizing antibodies on day 0 (pre-IPV) and on days 3, 7 and 21 (post-vaccination).

RESULTS

Complete data were available from 74.2% (728/981) subjects. Baseline median antibody titers were 713, 284, and 113 for poliovirus types 1, 2, and 3, respectively. Seroprevalence at study end were similar across the intervention groups (≥ 94.8%). The immune response induced with one new injector was similar to BCG needle and to the conventional injector; and superior to the other new injector. fIPV induced significantly lower boosting response compared to full-dose IPV. No safety concerns were identified.

INTERPRETATION

One of the two new injectors demonstrated its ability to streamline intradermal fIPV administration, however, further investigations are needed to assess the potential contribution of fIPV in the polio endgame plan.

Fully liquid DTaP-IPV-Hib pediatric combination vaccine (Pediacel): a review of 18 years of clinical experience

Safe and effective combination pediatric vaccines are necessary to simplify complex immunization schedules and to improve coverage and protection for children worldwide. We provide an overview of the 18 years of clinical and worldwide experience with DTaP-IPV-Hib (Pediacel(®)), a unique fully liquid pentavalent vaccine (diphtheria [D], tetanus [T], acellular pertussis, inactivated poliovirus [IPV], Haemophilus influenzae type b [Hib]). Pediacel has demonstrated good and lasting immunogenicity in many populations, with differing primary series and booster schedules, and with a variety of coadministered vaccines. The acellular pertussis antigens have proven efficacy and real-world effectiveness. Clinical and post-marketing studies confirm the safety of Pediacel. Pediacel can be used for primary series and toddler booster doses, as well as in mixed pediatric vaccine schedules.

Adaptation of enterovirus 71 to adult interferon deficient mice

Non-polio enteroviruses, including enterovirus 71 (EV71), have caused severe and fatal cases of hand, foot and mouth disease (HFMD) in the Asia-Pacific region. The development of a vaccine or antiviral against these pathogens has been hampered by the lack of a reliable small animal model. In this study, a mouse adapted EV71 strain was produced by conducting serial passages through A129 (α/β interferon (IFN) receptor deficient) and AG129 (α/β, γ IFN receptor deficient) mice. A B2 sub genotype of EV71 was inoculated intraperitoneally (i.p.) into neonatal AG129 mice and brain-harvested virus was subsequently passaged through 12 and 15 day-old A129 mice. When tested in 10 week-old AG129 mice, this adapted strain produced 100% lethality with clinical signs including limb paralysis, eye irritation, loss of balance, and death. This virus caused only 17% mortality in same age A129 mice, confirming that in the absence of a functional IFN response, adult AG129 mice are susceptible to infection by adapted EV71 isolates. Subsequent studies in adult AG129 and young A129 mice with the adapted EV71 virus examined the efficacy of an inactivated EV71 candidate vaccine and determined the role of humoral immunity in protection. Passive transfer of rabbit immune sera raised against the EV71 vaccine provided protection in a dose dependent manner in 15 day-old A129 mice. Intramuscular injections (i.m.) in five week-old AG129 mice with the alum adjuvanted vaccine also provided protection against the mouse adapted homologous strain. No clinical signs of disease or mortality were observed in vaccinated animals, which received a prime-and-boost, whereas 71% of control animals were euthanized after exhibiting systemic clinical signs (P<0.05). The development of this animal model will facilitate studies on EV71 pathogenesis, antiviral testing, the evaluation of immunogenicity and efficacy of vaccine candidates, and has the potential to establish correlates of protection studies.

Human febrile illness caused by encephalomyocarditis virus infection, Peru

Encephalomyocarditis virus was identified in the serum of 2 febrile patients in Peru.

Etiologic studies of acute febrile disease were conducted in sites across South America, including Cusco and Iquitos, Peru. Patients’ clinical signs and symptoms were recorded, and acute- and convalescent-phase serum samples were obtained for serologic examination and virus isolation in Vero E6 and C6/36 cells. Virus isolated in Vero E6 cells was identified as encephalomyocarditis virus (EMCV) by electron microscopy and by subsequent molecular diagnostic testing of samples from 2 febrile patients with nausea, headache, and dyspnea. The virus was recovered from acute-phase serum samples from both case-patients and identified with cardiovirus-specific reverse transcription–PCR and sequencing. Serum samples from case-patient 1 showed cardiovirus antibody by immunoglobulin M ELISA (acute phase <8, convalescent phase >1,024) and by neutralization assay (acute phase <10, convalescent phase >1,280). Serum samples from case-patient 2 did not contain antibodies detectable by either assay. Detection of virus in serum strongly supports a role for EMCV in human infection and febrile illness.

Long-lasting poliovirus-neutralizing antibodies among Argentinean population immunized with four or five oral polio vaccine doses 1 month to 19 years previously

The persistence of poliovirus-neutralizing antibodies was investigated in 297 individuals residing in Argentina who had completed the vaccination cycle with four or five oral polio vaccine (OPV) doses 1 mo to 19 yr before this study. Seropositivity for the three polio types in individuals who had received four OPV doses remained high and stable, showing rates not less than 94.6, 98.2, and 91.1% for types 1, 2, and 3, respectively, for a period of at least 6 yr. Almost identical rates were found in children who completed a vaccination schedule of five OPV doses 1 to 2 yr earlier. However, humoral immunity to poliovirus types 3 and 1 declined significantly 9 and 17 yr, respectively, after the booster dose had been administered; in contrast, type 2 immunity remained fairly stable during the 19-yr study period. Overall, geometric mean titer values for poliovirus types 1 and 2 were higher than those for poliovirus type 3. This is likely a result of low initial poliovirus type 3 antibody titers that eventually fell below the limits of detection at later time points. The results indicate that although antibody titers primed by OPV decline over time, they are remarkably long-lived, immunity to poliovirus types 1 and 2 being more prevalent than that against type 3 at late intervals postvaccination.

Survey of poliovirus antibodies during the final stage of polio eradication in Egypt

BACKGROUND

Egypt provides ideal conditions for poliovirus (PV) transmission (high population density, high contact rates and low sanitation and hygiene in some areas). Despite excellent program performance, wild poliovirus type 1 (PV1) continue to circulate in 2004. To investigate potential causes for the persistence, we conducted a serological study.

METHODS

Seroprevalence surveys were conducted in "polio-endemic" regions (Greater Cairo and Upper Egypt) and in one control region (Lower Egypt) in December 2004. Sera collected from infants aged 6-11 months were tested for antibodies to poliovirus by neutralization assay.

RESULTS

A total of 973 subjects were tested. Seroprevalence to PV type 1 (PV1), PV type 2 (PV2) and PV type 3 (PV3) was 99, 99 and 91%, respectively. Significant variation in PV3 seroprevalence was found (range: 76-100%). Region, density, maternal education, socioeconomic status (SES), stunting and diarrhea were significant risk factors for lower seroprevalence in the univariate analysis.

CONCLUSIONS

Our study suggested that uniformly high immunity levels (>96%) were required to interrupt PV1 transmission in the last remaining reservoirs (last PV1 was isolated in mid-January 2005 in Egypt). It further suggests substantial regional differences in OPV immunogenicity, with rural areas and low SES achieving the lowest seroprevalence to PV3.

Characterization of the homo- and heterotypic immune responses after natural norovirus infection

Noroviruses (NoV) are a genetically and antigenically diverse group of viruses that are common causes of outbreaks of gastroenteritis in humans of all ages. Limited information has been obtained on type specificity of the NoV immune response. In this study, we characterized the homologous and heterologous antibody responses in adults from 13 outbreaks, representing 4 different NoV genotypes. NoV specific IgG and IgA antibodies were determined as well as the increase of antibody avidity. In addition, antibody-mediated blocking of NoV binding to its putative receptor was evaluated. Both homologous and heterologous serological responses were detected after NoV infection. The avidity of antibodies could not be used to distinguish between homologous and heterologous antibody responses. However, a homologous blocking response but not a heterologous response was detected after infection with NoV belonging to genogroup II.4 by a NoV ligand binding inhibition assay. Infection with NoV induces antibodies that can block virus ligand interactions. In contrast with all currently known antibody detection assays for NoV, this can be used as a type specific assay and may be an alternative for studying neutralizing antibodies.

Does antigenic overload exist? The role of multiple immunizations in infants

There is no evidence that currently recommended vaccines overload or weaken the infant immune system. Infants have an enormous capacity to respond safely and effectively to multiple vaccines. The schedule for the administration of childhood vaccines is tailored to the unique developmental pattern of the infant immune system. Childhood vaccines provide immediate protection from common childhood illness and establish the foundation for lifelong immunity that develops with subsequent vaccination or infection. Widespread vaccination of infants and children represents a public health triumph of the 20th century. This fact must be reinforced continually by health care workers and parent education to help maintain progress in the 21st century.

Human monoclonal antibodies specific for conformation-sensitive epitopes of V3 neutralize human immunodeficiency virus type 1 primary isolates from various clades

The epitopes of the V3 domain of the human immunodeficiency virus type 1 (HIV-1) gp120 glycoprotein have complex structures consisting of linear and conformational antigenic determinants. Anti-V3 antibodies (Abs) recognize both types of elements, but Abs which preferentially react to the conformational aspect of the epitopes may have more potent neutralizing activity against HIV-1, as recently suggested. To test this hypothesis, human anti-V3 monoclonal Abs (MAbs) were selected using a V3 fusion protein (V3-FP) which retains the conformation of the third variable region. The V3-FP consists of the V3(JR-CSF) sequence inserted into a truncated form of murine leukemia virus gp70. Six human MAbs which recognize epitopes at the crown of the V3 loop were selected with the V3-FP. They were found to react more strongly with molecules displaying conformationally intact V3 than with linear V3 peptides. In a virus capture assay, these MAbs showed cross-clade binding to native, intact virions of clades A, B, C, D, and F. No binding was found to isolates from subtype E. The neutralizing activity of MAbs against primary isolates was determined in three assays: the GHOST cell assay, a phytohemagglutinin-stimulated peripheral blood mononuclear cell assay, and a luciferase assay. While these new MAbs displayed various degrees of activity, the pattern of cross-clade neutralization of clades A, B, and F was most pronounced. The neutralization of clades C and D viruses was weak and sporadic, and neutralization of clade E by these MAbs was not detected. Analysis by linear regression showed a highly significant correlation (P < 0.0001) between the strength of binding of these anti-V3 MAbs to intact virions and the percent neutralization. These studies demonstrate that human MAbs to conformation-sensitive epitopes of V3 display cross-clade reactivity in both binding to native, intact virions and neutralization of primary isolates.

Analysis of the relationship between immunogenicity and immunity for viral subunit vaccines

The prevention of viral infection by vaccination relies on stimulating an appropriate immune response in order to reduce the probability with which a virus can establish an infection. Post-vaccination antibody responses have therefore been associated with reducing the probability with which an individual can be infected (i.e., the vaccine's "impact"). Quantifying this relationship is essential in evaluating new vaccines, especially since comparisons between vaccines, and vaccine licensure, may be dependent on antibody responses alone. In this paper two principal questions are identified which need to be addressed in the evaluation of subunit vaccines: i) how do specific antibody levels relate to complete protection from infection or disease and ii) how do antigenic subunits interact in developing protection when combined together in a single vaccine. The aim is to identify explicitly certain assumptions that are frequently made implicitly in the discussion of vaccine action. First, antibody levels are related to levels of protection through a novel statistical analysis of incidence data from a published hepatitis B vaccine trial. The antibody response observed after influenza A virus infection is discussed in relation to the selection of neutralisation escape variants. Finally, by way of example, a theoretical situation is examined and three simple models of subunit vaccine action are constructed in order to describe how antibody levels may be related to population level phenomena such as the elimination of an infection by mass vaccination.

Humoral immunity against diphtheria, tetanus and poliomyelitis after antineoplastic therapy in children and adolescents--a retrospective analysis

Serum antibodies against diphtheria- and tetanus-toxin were measured in 71 children and against poliomyelitis viruses 1-3 in 65 children and adolescents 0-18 months after cessation of antineoplastic therapy. Non or marginally protective serum titers were found in 62% of patients against diphtheria, in 18% of patients against tetanus and in 72% of patients against one or more poliomyelitis virus serotypes. Of these patients, 55%, 46% and 75% were immunized adequately according to age against diphtheria, tetanus and poliomyelitis, respectively. In 50% or more of patients a lack of protective immunity against diphtheria, tetanus and poliomyelitis was found which could not be explained by an inadequate immunization status. This suggests that other factors (e.g. influence of underlying illness, antineoplastic therapy or both on lymphocytes) might be responsible for these findings and this deserves further investigation. Measurement of serum antibodies against vaccine-preventable illnesses and consecutive booster immunizations are an essential part of long-term follow up in pediatric patients after antineoplastic therapy.

New combination vaccines

Physicians can achieve full vaccination at each of the recommended visits by administering three or four injections, but for infants, four injections seem to be a maximum in light of the size of the infant thigh, which is the preferred injection site. Thus, physicians must make room for all of the new vaccines on the horizon. To accomplish that task, combinations will be necessary. Progress toward that goal is occurring.

Vaccination of infants with a four-dose and a three-dose vaccination schedule

Swedish infants were vaccinated with diphtheria, tetanus and pertussis toxoids, inactivated poliovirus vaccine and a Haemophilus influenzae type b - tetanus toxoid conjugate vaccine at 2, 4, 6 and 15 months (US vaccination program, 'US arm', n=118) or at 3, 5 and 12 months of age (Swedish vaccination program, 'Swedish arm', n=103). The antigen amounts in the diphtheria and tetanus vaccines were higher in the Swedish than in the US arm while the amounts in the other vaccines were the same in both arms. There were no serious side effects. Local reactions increased with the numbers of doses but did not differ significantly between the groups. Serum was obtained at 2, 7, 15 and 16 months in the US arm and at 3, 6, 12 and 13 months of age in the Swedish arm. A fifth serum was obtained in both groups at 4 yr of age. For vaccines with the same antigen amount the following was observed: a. three doses at 2, 4 and 6 months were more immunogenic than two doses at 3 and 5 months; b. the third dose in the Swedish arm was more immunogenic than the third dose in the US arm; c. the fourth dose in the US arm induced higher antibodies than the third dose in the Swedish arm (except for pertussis toxin antibodies that were similar in both groups) and the differences tended to remain at the age of 4 yr. Children in the Swedish arm received a higher diphtheria toxoid dose (25 Lf) than in the US arm (15 Lf) which led to higher diphtheria toxin antibodies in the Swedish arm at comparable ages. Children in the Swedish arm received a higher tetanus toxoid dose (7 Lf) than in the US arm (6 Lf). Tetanus antibodies were similar at comparable ages. In conclusion, the immunogenicity of vaccines in infancy can be improved by increasing the number of doses, by prolonging the intervals between doses and by increasing the antigen amount in the vaccine.

Multivalent vaccines: prospects and challenges

The advantages and disadvantages of combination vaccines are set out with a clear indication that, although there are many (described and discussed) influences on in the immunogenicity of a vaccine it would still be of considerable value to be able to deliver such materials with the minimum number of needle-stick injections. Such a situation may become facilitated in the future as vaccines based on plasmid DNA become available; a prospect which is examined in outline in the final section.