Potential impact of acceleration of the pertussis vaccine primary series for infants

Pertussis immunisation strategies to optimise infant pertussis control: A narrative systematic review

OBJECTIVE

Countries routinely offering acellular pertussis vaccine, where long-term protection is not sustained, have the challenge of selecting an optimal schedule to minimise disease among young infants. We conducted a narrative systematic review and synthesis of information to evaluate different pertussis immunisation strategies at controlling pertussis disease, hospitalisation, deaths, and vaccine effectiveness among young infants.

METHODS

We conducted a review of the literature on studies about the primary, booster, and/or maternal vaccination series and synthesised findings narratively. Countries offering the first three doses of vaccine within six-months of life and a booster on or before the second year or life were defined as accelerated primary and booster schedules, respectively. Countries offering primary and booster doses later were defined as extended primary and booster schedules. All search results were screened, and articles reviewed and reconciled, by two authors. The Risk of Bias in Non-randomised Studies of Intervention tool was used to evaluate the risk of bias.

FINDINGS

A total of 98 studies were included in the analyses and the following recurring themes were described: timing of vaccination, vaccine coverage, waning immunity/vaccine effectiveness, direct and indirect effectiveness, switching from an accelerated to extended schedule, impact of changes in testing. The risk of bias was generally low to moderate for most studies.

CONCLUSION

Comparing schedules is challenging and there was insufficient evidence to that one schedule was superior to another. Countries must select a schedule that maintains high vaccine coverage and reduced the risk of delaying the delivery vaccines to protect infants.

Pertussis immunisation during pregnancy: Antibody levels and the impact of booster vaccine

Pertussis (whooping cough) is a highly infectious disease caused by Bordetella pertussis. Mothers lacking adequate immunity and contracting the disease represent the biggest risk of transmission to new-borns, for which the disease is often a threat. The aim of the study was to estimate the frequency of pertussis susceptibility among pregnant women, in order to point out the need for a vaccine recall during pregnancy, and to evaluate the antibody response in already vaccinated women. A cross-sectional observational study was conducted in the blood test centre of "St. Anna" Obstetrics and Gynaecology Hospital in Turin (Piedmont, Italy). Eligibility criteria included pregnant women coming to the centre for any blood test, aged 18 or above and with gestational age between 33 and 37 weeks at the moment of the blood draw. The data collection was carried out from May 2019 to January 2020 and the concentration of anti-Pertussis Toxin (anti-PT) IgG was measured through the Enzyme-Linked Immunosorbent Assay (ELISA) technique. Two-hundred women (median age 35) were enrolled: 132 (66%) had received at least one dose of pertussis vaccine, 82 of which during pregnancy. Recently vaccinated women had significantly higher antibody titres (even 12-15 times as high) compared to those vaccinated more than 5 years before or never vaccinated at all (p < 0.0001). Moreover, 95.1% of recently vaccinated women had anti-PT IgG levels above 10 IU/ml, and 85.4% above 20 IU/ml, while the same proportions were as low as 37% and 21% (respectively) in the group of women not vaccinated in pregnancy. This study confirmed that the vaccination is greatly effective in ensuring high antibody titres in the first months after the booster vaccine, with considerable differences in anti-PT IgG compared to women vaccinated earlier or never vaccinated at all, and therefore vaccinating pregnant women against pertussis still represents a valuable strategy.

Potential Impact of Changes in the Schedule for Primary Diphtheria-Tetanus Toxoids-Pertussis Immunization as Control Strategy for Pertussis

BACKGROUND

Pertussis is a vaccine-preventable respiratory disease that may cause death mainly in infants. The schedules for primary pertussis vaccination are set in each country by the local health authorities. Several different schedules meet World Health Organization recommendations, 2-4-6 months, 6-10-14 weeks, 2-3-4 months and 3-4-5 months being the most commonly used worldwide. In this work, we analyze the benefits of changing the vaccination schedule to control the disease.

METHODS

We used an age-structured deterministic mathematical model for pertussis transmission to compute the incidences for the 4 above-mentioned schedules. Different vaccination coverages and vaccine effectiveness levels were considered. Immunization data from Argentina and Belgium were used.

RESULTS

The highest reduction in incidence was obtained by adopting the 6-10-14 weeks schedule, reaching about a 36% reduction of 0-1-year incidence with respect to the 2-4-6 months schedule. We show the dependence of this reduction on both vaccine effectiveness and coverage. The severe pertussis incidence decreased significantly when the first dose of the 2-4-6 months schedule was accelerated to 6 weeks. Finally, we estimated that the communication campaign adopted in Flanders (Belgium) to improve compliance with the vaccine schedule could lead to a reduction of 16% in severe pertussis incidence and about 7% in total incidence in infants.

CONCLUSIONS

Our work highlights the use of mathematical modeling to quantify the benefits of the existing vaccination schedules and the strategies that could be implemented to improve their compliance. Our results indicated that the 6-10-14 weeks is the best schedule option and that the Belgium vaccination campaign significantly reduced the incidence of severe cases.

Pertussis

Pertussis continues to be an important public-health issue. The high immunization coverage rates achieved, mainly in industrialized countries, have certainly decreased the spread of the pathogen. However, as immunity wanes, adolescents and adults play an important role in the dynamics of the infection. The surveillance system has several limitations and the underestimation of pertussis in adolescents, young adults and adults is mainly related to the atypical clinical characteristics of cases and the lack of lab confirmation. The real epidemiological impact of pertussis is not always perceived. The unavailability of comprehensive data should not hamper the adoption of active prophylactic measures designed to avoid the impact of waning immunity against pertussis. Different immunization strategies have been suggested and/or already adopted such as immunization of newborns, pre-school and school children, adolescents, adults, healthcare workers, childcare workers, pregnant women, cocoon strategy. Prevention of pertussis requires an integrated approach and the adoption of different immunization strategies, with the objective of achieving and maintaining high coverage rates.

Protecting newborns from pertussis - the challenge of complete cocooning

BACKGROUND

An increase of pertussis cases, especially in young infants and adolescents, has been noted in various countries. Whooping cough is most serious in neonates and young infants in whom it may cause serious complications such as cyanosis, apnoea, pneumonia, encephalopathy and death. To protect newborns and infants too young to be fully immunized, immunization of close contact persons has been proposed ("cocoon strategy") and implemented in several countries, including Switzerland in 2011. The goal of this study was to assess knowledge about pertussis among parents of newborns and acceptance, practicability and implementation of the recently recommended pertussis cocoon strategy in Switzerland.

METHODS

We performed a cross sectional survey among all parents of newborns born between May and September 2012 and 2013 in Basel city and country. Regional statistical offices provided family addresses after approval by the ethical and data protection committees. A standardized questionnaire with detailed instructions was sent to all eligible families. For statistical analyses, independent proportions were compared by Pearson's chi-squared test.

RESULTS

Of 3546 eligible parents, 884 (25%) participated. All three questions exploring pertussis knowledge were answered correctly by 37% of parents; 25% gave two correct answers, 22% gave one correct answer and in the remaining 16% no answer was correct. Pertussis immunization as part of cocooning was recommended to 20% and 37% of mothers and 14% and 32% of fathers in the 2012 and 2013 study cohorts, respectively. Principal advisors for cocooning were pediatricians (66%) followed by gynecologists/obstetricians (12%) and general practitioners (5%). When recommended, 64% of mothers and 59% of fathers accepted pertussis immunization. The majority of vaccinations were administered in the perinatal period and within 2 months of the child's birth. However, cocooning remained incomplete in 93% of families and in most families <50% of close contacts received pertussis vaccination.

CONCLUSIONS

Implementation of cocooning for protecting newborns from pertussis is challenging and usually remains incomplete. Pertussis immunization rates among close contacts of newborns need to be improved. Ideally, all healthcare providers involved in family planning, pregnancy and child birth should recommend cocooning. Pertussis immunization of pregnant women is an additional measure for optimal protection of newborns and should be promoted.

Perplexities of pertussis: recent global epidemiological trends and their potential causes

Recent much-publicized increases in pertussis case reports in some countries with high vaccine coverage have raised concerns about its current and future control. The ubiquity of this trend, however, remains unexamined. In an attempt to paint a global picture, we used case counts to determine which countries experienced statistically significant trends in incidence over the past two decades and to map changes in incidence during this period. These data reveal that pertussis resurgence is not a universal phenomenon. The heterogeneity in incidence trends, even in countries with superficially similar demography, socioeconomic conditions and vaccination programmes, is striking and requires explanation. In this opinion piece, we review and assess the multifaceted proposed explanations incorporating evolution, population dynamics, and the details of immunization programmes. While we do not solve the riddle that is pertussis epidemiology, we highlight critical aspects that are likely to hold the key to understanding its worldwide epidemiology.

Duration of protection after first dose of acellular pertussis vaccine in infants

OBJECTIVE

Data on the effectiveness of the diphtheria-tetanus-acellular pertussis (DTaP) vaccine in the first 4 years of life are sparse. We evaluated the vaccine effectiveness (VE) of 1 and 2 doses of DTaP before 6 months of age and of 3 doses from 6 months of age in Australia, where, since 2003, a fourth dose is not given until 4 years.

METHODS

We matched reported pertussis cases aged 2 to 47 months between January 2005 and December 2009 to controls from a population-based immunization register by date of birth and region of residence. VE by number of doses and age group was calculated as (1 - odds ratio) × 100%.

RESULTS

VE against hospitalization increased from 55.3% (95% confidence interval [CI], 42.7%-65.1%) for 1 dose before 4 months of age to 83.0% (95% CI, 70.2%-90.3%) for 2 doses before 6 months. The VE of 3 doses of DTaP against all reported pertussis was 83.5% (95% CI, 79.1%-87.8%) between 6 and 11 months, declining to 70.7% (95% CI, 64.5%-75.8%) between 2 and 3 years of age and 59.2% (95% CI, 51.0%-66.0%) between 3 and 4 years of age.

CONCLUSIONS

DTaP provided good protection against pertussis in the first year of life from the first dose. Without a booster dose, the effectiveness of 3 doses waned more rapidly from 2 to 4 years of age than previously documented for children >6 years of age who had received 5 doses.

Bordetella pertussis in infants hospitalized for acute respiratory symptoms remains a concern

BACKGROUND

Preliminary results suggest that pertussis infection might be considered in infants during a seasonal respiratory syncytial virus (RSV) outbreak.

METHODS

In order to analyze clinical features and laboratory findings in infants with pertussis hospitalized for acute respiratory symptoms during a seasonal RSV outbreak, we conducted a retrospective single-center study on 19 infants with pertussis (6 boys; median age 72 days) and 19 matched controls (RSV-bronchiolitis), hospitalized from October 2008 to April 2010. B. pertussis and RSV were detected from nasopharyngeal washes with Real Time-PCR.

RESULTS

Infants with pertussis were less often breastfeed than infants with RSV bronchiolitis (63.2% vs 89.5%; p <0.06). Clinically, significantly fewer infants with pertussis than controls had more episodes of whooping cough (63.2% vs 0.0%; p < 0.001) and also less frequently fever at admission (15.8% vs 68.4%; p <0.01), apnea (52.6% vs 10.5%; p <0.006), and cyanosis (52.6% vs 10.5%; p < 0.006). Infants with pertussis had more often no abnormal chest sounds on auscultation than infants with RSV bronchiolitis (0% vs 42,1%; p < 0.005). The absolute blood lymphocyte and eosinophil counts were higher in infants with B. pertussis than in controls with bronchiolitis (23886 ± 16945 vs 10725 ± 4126 cells/mm(3), p < 0.0001 and 13.653 ± 10.430 vs 4.730 ± 2.400 cells/mm(3), p < 0.001). The molecular analysis of 2 B. pertussis isolates for ptxA1, ptxP3, and prn2 genes showed the presence of gene variants.

CONCLUSIONS

When infants are hospitalized for acute respiratory symptoms, physicians should suspect a pertussis infection, seek for specific clinical symptoms, investigate lymphocyte and eosinophil counts and thus diagnose infection early enough to allow treatment.

Strategies to control pertussis in infants

The UK is currently in the midst of a large outbreak of pertussis, with the highest morbidity and mortality occurring in young unimmunised infants. This review considers the potential strategies to optimise control of pertussis in infants, including vaccination of (1) adolescents, (2) close household contacts of newborn infants (cocooning), (3) newborn infants and (4) pregnant women. The paper discusses the evidence base for each of these strategies and considers the rationale for the recent introduction of a temporary vaccination programme for pregnant women in the UK in response to the ongoing outbreak.

Infectious diseases and vaccination strategies: how to protect the "unprotectable"?

Introduction. The circulation of infectious diseases puts small infants too young to be vaccinated at risk of morbidity and mortality, often requiring prolonged hospitalization. Material and Methods. We have reviewed the medical records of children not eligible for vaccination because of age, admitted to hospital for pertussis, measles, or varicella from February 1, 2010, till February 1, 2012. Results. Of the case records scrutinized, 21 were hospitalized for pertussis, 18 for measles, and 32 for varicella. Out of them, 42%, 66%, and 78% diagnosed with, respectively, pertussis, measles, and varicella had a complicated course of the disease. Discussion. To avoid infectious disease circulation, childhood immunization strategies should be adopted, such as vaccination of healthcare givers, adult household contacts, and parents planning to have, or who have had, a newborn baby.

Potential impact of accelerating the primary dose of rotavirus vaccine in infants

We estimated the potential impact of administering the first dose of rotavirus vaccine at 6 weeks (42 days of life) instead of 2 months of age, which is permissible for all U.S. vaccines recommended at 2 months of age, on rotavirus hospitalization rates. We used published data for hospitalization rates, vaccine coverage, and vaccine efficacy after one dose and assumed a two-week delay in seroconversion after vaccine administration in the United States. Administering the first dose of rotavirus vaccine at 6 weeks instead of 8 weeks of age should have prevented 1110, 1660, and 2210 rotavirus hospitalizations among U.S. infants <3 months of age in 2006 when the vaccine was first introduced. This estimated benefit represents a 2-4% reduction in rotavirus hospitalizations among children <5 years of age.

Kinetics of the antibody response to tetanus-diphtheria-acellular pertussis vaccine in women of childbearing age and postpartum women

BACKGROUND

Because adolescents and adults act as a primary source of pertussis infection for infants, vaccination of mothers immediately postpartum is a potential strategy to reduce transmission (cocoon strategy). For this to be effective, high levels of antibodies must be achieved rapidly after vaccination. We sought to determine whether the antibody response to tetanus-diphtheria-acellular pertussis vaccine (Tdap) is sufficiently rapid to support the cocoon strategy.

METHODS

Two sequential studies were performed. The first was a nonrandomized, open study of a 5-pertussis-component Tdap vaccine (tetanus toxoid, diphtheria toxoid, pertussis toxoid [PT], filamentous hemagglutinin [FHA], fimbriae types 2 and 3 [FIM], and pertactin [PRN]) given to women of childbearing age; the second was a randomized, open study of Tdap or no vaccine in postpartum women. Serum levels of immunoglobin (Ig) G and IgA against pertussis antigens, serum levels of IgG against diphtheria and tetanus, and breast milk levels of IgA against pertussis antigens were measured at various times after vaccination.

RESULTS

In both studies, the antibody response was relatively rapid, with serum IgG and IgA levels beginning to increase noticeably by days 5-7 and approaching peak levels by day 14. Greater than 68% and 84.4% of IgG and IgA responders, respectively, achieved ≥ 90% of their maximum titer by day 14. The diphtheria and tetanus antibody kinetics followed a similar time course. Breast milk levels of IgA against PT, FHA, and FIM were first detectable at day 7, peaked by day 10, and then slowly decreased through day 28. Antibodies against PRN showed a similar response, although the peak occurred at day 14. There were no significant antibody responses in the control group.

CONCLUSIONS

Although the antibody response to a dose of Tdap in healthy nonpregnant women of child-bearing age and postpartum women occurs by day 14 and is suggestive of an anamnestic immune response, it may not be sufficiently rapid to protect infants in the first weeks of life.

Severe pertussis in infants: estimated impact of first vaccine dose at 6 versus 8 weeks in australia

We estimated the potential benefits of advancing the first dose of pertussis vaccine for infants from 8 to 6 weeks of age, using Australian national disease databases. Infants had notification rates 3-fold greater than the general population and accounted for 52% of recorded hospitalizations. Infants 1 and 2 months of age had notification rates 3.5 times (95% CI: 2.7-4.5) higher than infants 3 to 11 months of age. Estimation of acceleration of the vaccine to 6 weeks of age reduced average notifications, hospitalizations, and hospital bed-days by 8%, 9%, and 12%, respectively, with larger reductions in an epidemic year.

Feasibility and impact of providing feedback to vaccinating medical clinics: evaluating a public health intervention

Background

Vaccine coverage (VC) at a given age is a widely-used indicator for measuring the performance of vaccination programs. However, there is increasing data suggesting that measuring delays in administering vaccines complements the measure of VC. Providing feedback to vaccinators is recognized as an effective strategy for improving vaccine coverage, but its implementation has not been widely documented in Canada. The objective of this study was to evaluate the feasibility of providing personalized feedback to vaccinators and its impact on vaccination delays (VD).

Methods

In April and May 2008, a one-hour personalized feedback session was provided to health professionals in vaccinating medical clinics in the Quebec City region. VD for vaccines administered at two and twelve months of age were presented. Data from the regional vaccination registry were analysed for participating clinics. Two 12-month periods before and after the intervention were compared, namely from April 1^st, 2007 to March 31^st, 2008 and from June 1^st, 2008 to May 31^st, 2009.

Results

Ten medical clinics out of the twelve approached (83%), representing more than 2500 vaccinated children, participated in the project. Preparing and conducting the feedback involved 20 hours of work and expenses of $1000 per clinic. Based on a delay of one month, 94% of first doses of DTaP-Polio-Hib and 77% of meningococcal vaccine doses respected the vaccination schedule both before and after the intervention. Following the feedback, respect of the vaccination schedule increased for vaccines planned at 12 months for the four clinics that had modified their vaccination practices related to multiple injections (depending on the clinic, VD decreased by 24.4%, 32.0%, 40.2% and 44.6% respectively, p < 0.001 for all comparisons).

Conclusions

The present study shows that it is feasible to provide personalized feedback to vaccinating clinics. While it may have encouraged positive changes in practice concerning multiple injections, this intervention on its own did not impact vaccination delays of the clinics visited. It is possible that feedback integrated into other types of effective interventions and sustained over time may have more impact on VD.

Potential impact of accelerating the primary dose of pneumococcal conjugate vaccine in infants

OBJECTIVE

To estimate the potential effect of the acceleration of administration of the first dose of pneumococcal conjugate vaccine from 2 months to 6 weeks of age.

DESIGN

Prediction model using data from a retrospective cohort study.

SETTING

Published data from 8 states that participated in Active Bacterial Core Surveillance of the Emerging Infections Program Network for pneumococcus before pneumococcal conjugate vaccine introduction (July 1, 1997- June 30, 2000).

PARTICIPANTS

A total of 759 739 live births under surveillance. Intervention Estimating the potential benefit of administration of the first dose of the pneumococcal conjugate vaccine at 6 weeks of age instead of 2 months of age.

MAIN OUTCOME MEASURES

Estimation of reduction in the rate of invasive pneumococcal disease in infants 61 to 90 days of age.

RESULTS

The estimated direct effect of the acceleration of administration of the first dose of pneumococcal conjugate vaccine from 2 months to 6 weeks of age when this vaccine was first introduced could have reduced the burden of invasive pneumococcal disease in infants 61 to 90 days of age by 39.9%, 56.0%, and 72.1% for respective vaccine efficacies of 50%, 70%, and 90%. This translates into preventing an estimated 73, 103, and 133 cases of invasive pneumococcal disease per year among approximately 4 112 052 live births in the United States.

CONCLUSIONS

The acceleration of administration of the pneumococcal conjugate vaccine from 2 months to 6 weeks of age could reduce the burden of invasive pneumococcal disease among infants. This observation may be important when a new conjugate vaccine becomes available, particularly among populations with prevalent invasive pneumococcal disease from a serotype included in the new vaccine.