European sero-epidemiology network: standardisation of the results of diphtheria antitoxin assays

Diphtheria and Tetanus Immunity Status among Greek Adults: Results from a Nationwide Seroprevalence Study

Diphtheria and tetanus could lead to serious morbidity. We aimed to evaluate immunity levels by measuring specific IgG antibodies for diphtheria and tetanus in serum samples from a nationally expanded sample of the Greek population. A geographically stratified sampling approach based on regional units (NUTS level 2) was applied by considering variables such as age group (30-80+) and sex. In total, 1201 persons (47.7% males and 52.3% females) participated in the survey. Bivariate analysis revealed a negative relationship between diphtheria and tetanus median antibody titers and age. The overall seropositivity rate for diphtheria IgG antibodies (≥0.10 IU/mL) was estimated at 31.5%. Regarding tetanus, the total seropositivity rate was estimated at 59.5% (tetanus IgG antibodies ≥0.10 IU/mL). Logistic regression analysis indicated that age groups <40 years and 40-59 years were independently associated with tetanus seropositivity. Logistic regression also revealed that male sex and being aged 60-69 years were independent risk factors for diphtheria-related seropositivity. Lastly, being resident of some regions was an independent risk factor for both diphtheria- and tetanus-related seropositivity. The present study shows that Greek adults are still not completely immune to diphtheria and tetanus. It is likely possible to achieve optimal immunization coverage by implementing serviceable public health initiatives after comprehending real community needs.

Circulation of pertussis and poor protection against diphtheria among middle-aged adults in 18 European countries

Reported incidence of pertussis in the European Union (EU) and the European Economic Area (EEA) varies and may not reflect the real situation, while vaccine-induced protection against diphtheria and tetanus seems sufficient. We aimed to determine the seroprevalence of DTP antibodies in EU/EEA countries within the age groups of 40-49 and 50-59 years. Eighteen countries collected around 500 samples between 2015 and 2018 (N = 10,302) which were analysed for IgG-DTP specific antibodies. The proportion of sera with pertussis toxin antibody levels ≥100 IU/mL, indicative of recent exposure to pertussis was comparable for 13/18 countries, ranging between 2.7-5.8%. For diphtheria the proportion of sera lacking the protective level (<0.1 IU/mL) varied between 22.8-82.0%. For tetanus the protection was sufficient. Here, we report that the seroprevalence of pertussis in these age groups indicates circulation of B. pertussis across EU/EEA while the lack of vaccine-induced seroprotection against diphtheria is of concern and deserves further attention.

A phase I, randomized, controlled, dose-ranging study of investigational acellular pertussis (aP) and reduced tetanus-diphtheria-acellular pertussis (TdaP) booster vaccines in adults

Despite high vaccination coverage worldwide, pertussis has re-emerged in many countries. This randomized, controlled, observer-blind phase I study and extension study in Belgium (March 2012-June 2015) assessed safety and immunogenicity of investigational acellular pertussis vaccines containing genetically detoxified pertussis toxin (PT) (NCT01529645; NCT02382913). 420 healthy adults (average age: 26.8 ± 5.5 years, 60% female) were randomized to 1 of 10 vaccine groups: 3 investigational aP vaccines (containing pertussis antigens PT, filamentous hemagglutinin [FHA] and pertactin [PRN] at different dosages), 6 investigational TdaP (additionally containing tetanus toxoid [TT] and diphtheria toxoid [DT]), and 1 TdaP comparator containing chemically inactivated PT. Antibody responses were evaluated on days 1, 8, 30, 180, 365, and approximately 3 years post-booster vaccination. Cell-mediated immune responses and PT neutralization were evaluated in a subset of participants in pre-selected groups. Local and systemic adverse events (AEs), and unsolicited AEs were collected through day 7 and 30, respectively; serious AEs and AEs leading to study withdrawal were collected through day 365 post-vaccination. Antibody responses against pertussis antigens peaked at day 30 post-vaccination and then declined but remained above baseline level at approximately 3 years post-vaccination. Responses to FHA and PRN were correlated to antigen dose. Antibody responses specific to PT, toxin neutralization activity and persistence induced by investigational formulations were similar or significantly higher than the licensed vaccine, despite lower PT doses. Of 15 serious AEs, none were considered vaccination-related; 1 led to study withdrawal (premature labor, day 364; aP4 group). This study confirmed the potential benefits of genetically detoxified PT antigen. All investigational study formulations were well tolerated.

Estimating seroprevalence of vaccine-preventable infections: is it worth standardizing the serological outcomes to adjust for different assays and laboratories?

The aim of the European Sero-Epidemiology Network 2 (ESEN2) project was to estimate age-specific seroprevalence for a number of vaccine-preventable diseases in Europe. To achieve this serosurveys were collected by 22 national laboratories. To adjust for a variety of laboratory methods and assays, all quantitative results were transformed to a reference laboratory's units and were then classified as positive or negative to obtain age-specific seroprevalence. The aim of this study was to assess the value of standardization by comparing the crude and standardized seroprevalence estimates. Seroprevalence was estimated for measles, mumps, rubella, diphtheria, varicella zoster and hepatitis A virus (HAV) and compared before and after serological results had been standardized. The results showed that if no such adjustment had taken place, seroprevalence would have differed by an average of 3·2% (95% bootstrap interval 2·9-3·6) although this percentage varied substantially by antigen. These differences were as high as 16% for some serosurveys (HAV) which means that standardization could have a considerable impact on seroprevalence estimates and should be considered when comparing serosurveys performed in different laboratories using different assay methods.

Issues and considerations in the use of serologic biomarkers for classifying vaccination history in household surveys

Accurate estimates of vaccination coverage are crucial for assessing routine immunization program performance. Community based household surveys are frequently used to assess coverage within a country. In household surveys to assess routine immunization coverage, a child's vaccination history is classified on the basis of observation of the immunization card, parental recall of receipt of vaccination, or both; each of these methods has been shown to commonly be inaccurate. The use of serologic data as a biomarker of vaccination history is a potential additional approach to improve accuracy in classifying vaccination history. However, potential challenges, including the accuracy of serologic methods in classifying vaccination history, varying vaccine types and dosing schedules, and logistical and financial implications must be considered. We provide historic and scientific context for the potential use of serologic data to assess vaccination history and discuss in detail key areas of importance for consideration in the context of using serologic data for classifying vaccination history in household surveys. Further studies are needed to directly evaluate the performance of serologic data compared with use of immunization cards or parental recall for classification of vaccination history in household surveys, as well assess the impact of age at the time of sample collection on serologic titers, the predictive value of serology to identify a fully vaccinated child for multi-dose vaccines, and the cost impact and logistical issues on outcomes associated with different types of biological samples for serologic testing.

A phase III single arm, multicenter, open-label study to assess the immunogenicity and tolerability of a pentavalent DTwP-HepB-Hib vaccine in indian infants

Compliance with recommended vaccinations for Indian infants is facilitated by using combination vaccines to minimize the number of required injections. The ready-to-use, preservative free, fully-liquid combination DTwP-HepB-Hib vaccine, Quinvaxem(®), offers convenience of administering five important vaccine antigens to infants in a single injection. This phase III, single-arm, multicenter study was designed to assess immunogenicity and safety of three doses of Quinvaxem(®) to Indian infants administered at 6, 10, and 14 weeks of age. Blood samples were taken prior to the first dose and at one month post last vaccination. Infants were observed clinically for any reaction approximately 30 min following each vaccination, and parents completed subject diaries for solicited local, systemic and any adverse events (AEs) following over a 5 d period. DTwP-HepB-Hib vaccine elicited strong immune responses that exceeded seroprotection/seroconversion thresholds against all vaccine antigens. At one month after third vaccination, percentages of infants achieving predefined protective antibody levels were 99% diphtheria; 100% tetanus; 98% Hepatitis B; 100% Hib short-term (≥ 0.15 µg/mL); 95% Hib long-term (≥ 1.0 µg/mL) protection; and relevant immune response was 99% for pertussis. The vaccine was well tolerated, with no vaccine-related serious AEs. Only one case of high fever (≥ 40 °C) was reported. The most frequently reported reactions were mild to moderate tenderness and erythema. Frequencies of all AEs declined with subsequent vaccinations. This study demonstrated that this convenient, fully-liquid DTwP-HepB-Hib vaccine is highly immunogenic and has a acceptable safety profile for use in Indian infants. ClinicalTrials.gov Identifier: NCT01470287. Clinical Trials Registry of India Number: CTRI/2011/11/002118.

Lot-to-lot consistency study of the fully liquid pentavalent DTwP-HepB-Hib vaccine Quinvaxem (®) demonstrating clinical equivalence, suitability of the vaccine as a booster and concomitant administration with measles vaccine

This double-blind, randomized study evaluated the immunogenicity and safety of three production lots of the fully liquid combination DTwP-Hep-Hib vaccine, Quinvaxem (®) (Crucell, The Netherlands) in 360 healthy infants aged 42-64 d old given at 6, 10 and 14 weeks of age (Core Study). The Core Study was followed by an open-label Booster Phase evaluating immunogenicity and safety of a booster dose of Quinvaxem (®) given with either concomitant or deferred measles vaccine in 227 infants who completed the Core Study. One month after the third dose of Quinvaxem (®) immune responses reflecting seroprotection or seroconversion were observed in more than 90% of infants for all three vaccine lots. Quinvaxem (®) elicited a strong booster response as demonstrated by a large increase in antibodies against all antigens, which appeared to be unaffected by concomitant administration of the measles vaccine. Safety results were in line with previous reports for Quinvaxem (®) with no unexpected adverse events (AEs) being reported. In the Core Study and Booster Phase, Quinvaxem (®) was well tolerated. No study vaccine-related serious AEs were reported. Thus, Quinvaxem (®) was immunogenic and well-tolerated when administered to infants according to a 6-10-14 week vaccination schedule. The three production lots had consistent reactogenicity and immunogenicity profiles. The booster dose of Quinvaxem (®) was also immunogenic and safe, regardless of whether a monovalent measles vaccine was administered concomitantly or one month later.

Comparative seroepidemiology of diphtheria in six European countries and Israel

Serological surveys for diphtheria were conducted in six European countries including Czech Republic, Hungary, Ireland, Latvia, Luxembourg, Slovakia and one country outside Europe, Israel. For each country, a nationally representative population sample was collected across the entire age range and was tested for antibodies to diphtheria toxin. Although each national laboratory used its preferred assay, the results were all standardized to those of the in vitro neutralization test and expressed in international units (IU) which allowed comparative analyses to be performed. The results showed that increasing age is related to a gradual increase in seronegative subjects (<0·01 IU/ml of diphtheria antitoxin antibodies). This may reflect waning immunity following childhood vaccination without repeated booster vaccinations in adults. Differences in seronegativity were also found according to gender. In subjects aged 1-19 years, geometric mean titres of antitoxin are clearly related to the different vaccination schedules used in the participating countries. Although clinical disease remains rare, the susceptibility to diphtheria observed in these serosurveys highlights the importance of strengthened surveillance.

External quality assessment for the determination of diphtheria antitoxin in human serum

Accurate determination of diphtheria toxin antibodies is of value in determining the rates of immunity within broad populations or the immune status of individuals who may be at risk of infection, by assessing responses to vaccination and immunization schedule efficacy. Here we report the results of an external quality assessment (EQA) study for diphtheria serology, performed within the dedicated surveillance network DIPNET. Twelve national laboratories from 11 European countries participated by testing a standard panel of 150 sera using their current routine method: Vero cell neutralization test (NT), double-antigen enzyme-linked immunosorbent assay (ELISA; DAE), dual double-antigen time-resolved fluorescence immunoassay (dDA-DELFIA), passive hemagglutination assay (PHA), toxin binding inhibition assay (ToBI), and in-house or commercial ELISAs. The objective of the study was not to identify the best assay, as the advantages and drawbacks of methods used were known, but to verify if laboratories using their routine method would have categorized (as negative, equivocal, or positive) a serum sample in the same way. The performance of each laboratory was determined by comparing its results on a quantitative and qualitative basis to NT results from a single reference laboratory, as this test is considered the in vitro "gold standard." The performance of laboratories using NT was generally very good, while the laboratories' performance using other in vitro methods was variable. Laboratories using ELISA and PHA performed less well than those using DAE, dDA-DELFIA, or ToBI. EQA is important for both laboratories that use in vitro nonstandardized methods and those that use commercial ELISA kits.

IL-2 producing memory CD4+ T lymphocytes are closely associated with the generation of IgG-secreting plasma cells

The role of specific CD4(+) T cell subsets in the induction of humoral immune responses in humans is largely unknown. In this study, the generation of hepatitis B surface Ag-specific CD4(+) T lymphocytes following vaccination was closely monitored and characterized at the single-cell level. The appearance and absolute numbers of hepatitis B surface Ag-specific IL-2 producing effector memory CD4(+) T lymphocytes was solely and tightly related to Ab titers reached. This relation remained present many years after vaccination. Subsequently, a relation was found between Ab titers and number of IL-2 producing memory CD4(+) T lymphocytes for various other Ags. These observations matched the findings of an in vitro assay, using different T cell subsets to induce B cell differentiation into IgG-producing plasma cells. By depleting for IL-2 producing memory T cells, we demonstrated that these cells are important for B cell differentiation into IgG-producing plasma cells. Finally, blocking the action of IL-2 with an IL-2R-alpha Ab inhibited the differentiation of B lymphocytes into IgG-producing plasma cells. Based on these findings, we conclude that the development of Ag-specific IL-2-producing memory T cells appears to be essential for the development of IgG-secreting plasma cells in humans.

The European Sero-Epidemiology Network 2 (ESEN2): standardization of assay results for hepatitis A virus (HAV) to enable comparisons of seroprevalence data across 15 countries

The European Sero-Epidemiology Network 2 (ESEN2) aimed to compare serological results of vaccine-preventable diseases across Europe. To ensure direct inter-country comparability of hepatitis A virus antibody (anti-HAV) measurements, a standardization panel of 150 sera was developed by a designated reference laboratory and tested by participating national laboratories using assays of choice; each country's results were subsequently regressed against those of the reference laboratory. Quantitatively, the assays were generally highly correlated (R2>0·90). Nevertheless, qualitative comparisons indicated that results obtained with different assays may differ despite the usage of well-established international and local standards. To a great extent standardization successfully alleviated such differences. The generated standardization equations will be used to convert national serological results into common units to enable direct international comparisons of HAV seroprevalence data. The results of this study are expected to contribute to the evaluation and potential improvement of the currently employed immunization strategies for hepatitis in Europe.

European Sero-Epidemiology Network 2: standardisation of immunoassay results for pertussis requires homogeneity in the antigenic preparations

A standardisation process, already developed during the earlier European Sero-Epidemiology Network (ESEN) project, was employed with a more robust algorithm to harmonise results of pertussis serological assays performed in 12 European and non-European countries. Initially, results from each country's own assay were compared with those obtained at the reference laboratory by means of an in-house pertussis toxin (PT)-based ELISA: seven countries used in-house or commercial PT-ELISAs; the other countries used assays based on Bordetella pertussis whole cell extracts (WCE) (three countries) or on combined PT-FHA (filamentous haemagglutinin) antigenic preparations (two countries). The WCE assays, although admitted for diagnostic purposes, confirmed their low correlation with the PT-ELISAs and their results could not be used for standardisation; the PT-FHA ELISAs gave results that were suitable for standardisation in one country but unsatisfactory in the other; the use of purified PT in serological assays confirmed its better reliability than other preparations and all PT-ELISAs results could be calibrated against those of the reference centre. In the standardisation process two high-titre cut-offs indicative of likelihood of recent infection (from within 4 weeks of disease onset up to 1 year after) were included for evaluations as they are suggested to be more useful, for the sero-epidemiological assays of immunity to pertussis, than the cut-off of protection, commonly employed, but still not defined for pertussis. Providing PT-ELISAs are used, standardisation of pertussis assay results is always possible and, when standardisation is performed, evaluation and comparison of the impact of different interventions can be also allowed, by measuring at the distribution of high antibody titres in the populations.

Development and validation of a multiplex immunoassay for the simultaneous determination of serum antibodies to Bordetella pertussis, diphtheria and tetanus

To increase testing of vaccine induced humoral immunity in immune surveillance studies and vaccine trials, a rapid and simple microsphere-based multiplex assay (pentaplex) was developed for the quantitation of IgG serum antibodies directed against the Bordetella pertussis antigens: Pertussis Toxin (Ptx), Filamentous hemagglutinin (FHA), Pertactin (Prn) and to Diphtheria toxin and Tetanus toxin. All individual antigens were covalently linked to carboxylated microspheres. The method was validated with different serum panels (n=60-78 samples). With the Multiplex Immunoassay (MIA) no evidence for bead interference between monoplex and pentaplex was found. The specificity of the method was shown by a heterologous inhibition of <16% and homologous inhibition of >92%. The pentaplex MIA appeared sensitive with lower limits of quantitation (LLOQ) well below those for ELISA (enzyme-linked immuno-sorbant assay). Assay reproducibility was high with intra-assay variability less than 10% and inter-assay variability below 14%. The reproducibility of the bead conjugation was good and beads could be stored up to at least 6 months without quality reduction. Importantly, the correlation of the pentaplex MIA with the individual ELISAs was excellent, R>0.98 for the Pertussis antigens and R=0.95 for Diphtheria and R=0.98 for Tetanus. Serum IgG antibodies to B. pertussis, Diphtheria and Tetanus can be measured easily, specific and reproducible using the pentaplex MIA. The pentaplex MIA shares features of the ELISA with the additional advantages of high sample throughput and small sample volumes and antigen required.

Diphtheria, tetanus, and varicella immunity in health care workers in neonatal units

BACKGROUND

Susceptible health care workers are at risk of acquiring and transmitting vaccine-preventable diseases to or from patients. The objective of this study was to assess antibody levels against diphtheria, tetanus, and varicella in healthcare workers.

METHODS

Antibody levels against diphtheria, tetanus, and varicella were measured in health care professionals in 2 neonatal units at the Federal University of São Paulo, Brazil.

RESULTS

Between September and November 2002, 215 of 222 (96.8%) health care workers were studied. Of those, 122 (56.7%) gave oral information regarding their vaccination status against diphtheria and tetanus and only 9 (4.2%) had their vaccination cards. Geometric mean antibody levels against diphtheria, tetanus, and varicella were 0.89 IU/mL (95%CI, 0.73 to 1.08), 0.86 IU/mL (95%CI, 0.68 to 1.07) and 1.10 IU/mL (95%CI, 0.98 to 1.24), respectively. Using internationally accepted definitions, 200 (93.0%) and 182 (84.7%) individuals had full protection against diphtheria and tetanus, respectively. Regarding varicella, 213 (99.1%) individuals were immune and 2 (0.9%) had equivocal immunity against varicella. Of 65 (30.2%) individuals without previous history of the illness, 63 (96.9%) were immune against varicella zoster virus.

CONCLUSIONS

Based on serologic screening, most professionals were immune to diphtheria, tetanus, and varicella. Absence of previous history of varicella was an unreliable identifier of susceptibility to varicella zoster virus in the health care workers studied.

Evaluation of human antibody responses to diphtheria toxin subunits A and B in various age groups

This study aimed to evaluate human antibody responses to diphtheria toxin subunits in various age groups. Antibodies against the intact diphtheria toxin and the diphtheria toxin subunits A and B were evaluated in 1319 individuals using a double-antigen ELISA. Although high levels of protection (83.6%, 95% CI 79.2-87.4) were found in children and adolescents, the middle-aged adult population was less protected (28.8%, 95% CI 24.3-33.6). An increase in age was associated with a decrease in the frequency of protected individuals in the 0-39-year age group (p <0.001). Anti-subunit B levels correlated well (p <0.01) with levels of antibodies against the intact toxin. In children aged < or =16 years, the intervals at which the peaks in geometric mean titres of anti-subunit B antibodies were observed were found to correlate with the ages at which booster doses are administered. Overall, males appeared to be more protected than females (OR 1.67, 95% CI 1.34-2.08, p <0.001). A small group of individuals had antibody levels of > or =0.1 IU/mL against the intact toxin, but did not have protective antibody against subunit B. Determination of anti-subunit B antibody levels should help in evaluating the effectiveness of diphtheria boosters and other aspects of diphtheria immunity.

The European Sero-Epidemiology Network 2: standardization of assay results for hepatitis B virus

The aim of the European Sero-Epidemiology Network 2 was to coordinate and standardize the serological surveillance of vaccine-preventable diseases in Europe. In this study, the standardization of hepatitis B virus (HBV) results is described. The 15 participating national laboratories tested a unique panel of 172 sera established by the Greek reference centre for HBV surface antigen (HBsAg), antibodies to HBsAg (anti-HBs) and/or to the HBV core antigen (anti-HBc) by assay methods of their choice. Country-specific quantitative measurements for anti-HBs and anti-HBc were transformed into common units using standardization equations derived by regressing each country's panel results against the reference centre's results, thus adjusting for interassay and interlaboratory variability. For HBsAg, a qualitative analysis (positive/negative) showed at least 99% agreement with the reference laboratory for all countries. By combining these standardized and qualitative results for the markers mentioned earlier, it was possible to achieve comparable estimates of the proportion of the population susceptible to HBV, vaccinated against HBV, with a past HBV infection, and with a current infection or chronic carrier state. Standardization is a very important tool that allows for international serological comparisons to assess the current vaccination policies and the progress of HBV control in Europe.

European seroepidemiology network 2: Standardisation of assays for seroepidemiology of varicella zoster virus

BACKGROUND

The aim of the European Sero-Epidemiology Network (ESEN2) is to harmonise the serological surveillance of vaccine-preventable diseases in Europe.

OBJECTIVE

To allow comparison of antibody prevalence in different countries by standardising results into common units.

STUDY DESIGN

For varicella zoster virus (VZV), a reference laboratory established a panel of 148 samples, characterised by indirect enzyme-immunoassay (ELISA), indirect immunofluorescence, and complement fixation test. Fifty-seven samples were also studied by the fluorescence antibody to membrane antigen test. The geometric mean of the antibody activity (GMAA) obtained from four ELISA determinations was used to characterise each sample of the panel as positive (GMAA: >100 mIU/ml), equivocal (GMAA: 50-100 mIU/ml) or negative (GMAA: <50 mIU/ml) for antibody to VZV (anti-VZV). Thirteen laboratories, using five different ELISA tests, tested the panel.

RESULTS

Agreement with the reference laboratory was above 85% in all cases, and the R(2) values obtained from regression analysis of the quantitative results were always higher than 0.87. Finally, the regression equations could be used to convert national values into a common unitage.

CONCLUSION

This study confirmed that results for anti-VZV obtained by different ELISA methods can be converted into common units, enabling the comparison of the seroprevalence profiles obtained in the participant countries.

Performance of a time-resolved fluorescence immunoassay for measuring varicella-zoster virus immunoglobulin G levels in adults and comparison with commercial enzyme immunoassays and Merck glycoprotein enzyme immunoassay

Highly sensitive and specific, quantitative assays are needed to detect varicella-zoster virus (VZV) immunoglobulin G in human sera, particularly for determining immune status and response following vaccination. A time-resolved fluorescence immunoassay (TRFIA) has been developed, and its performance was compared to that of two commercial enzyme immunoassays (EIAs) and Merck glycoprotein EIA (gpEIA). The TRFIA had equivalent sensitivity (97.8%) and high specificity (93.5%) in relation to gpEIA. A commercial (Behring) EIA compared favorably with TRFIA in terms of sensitivity (98.4%) but had lower specificity (80.7%). Another commercial EIA (Diamedix) had high specificity (97.1%) but low sensitivity (76.4%) compared to TRFIA if equivocal test results were treated as negative for VZV antibody. A novel feature of the TRFIA was that the cutoff was generated using population mixture modeling and was expressed in mIU/ml, as the assay was calibrated using the British standard VZV antibody.

Effect of a single tetanus-diphtheria vaccine dose on the immunity of elderly people in São Paulo, Brazil

Epidemiological data regarding tetanus and diphtheria immunity in elderly people in Brazil are scarce. During the First National Immunization Campaign for the Elderly in Brazil in April 1999, 98 individuals (median age: 84 years) received one tetanus-dyphtheria (Td) vaccine dose (Butantan Institute, lot number 9808079/G). Inclusion criteria were elderly individuals without a history of severe immunosuppressive disease, acute infectious disease or use of immunomodulators. Blood samples were collected immediately before the vaccine and 30 days later. Serum was separated and stored at -20 degrees C until analysis. Tetanus and diphtheria antibodies were measured by the double-antigen ELISA test. Tetanus and diphtheria antibody concentrations lower than 0.01 IU/mL were considered to indicate the absence of protection, between 0.01 and 0.09 IU/mL were considered to indicate basic immunity, and values of 0.1 IU/mL or higher were considered to indicate full protection. Before vaccination, 18% of the individuals were susceptible to diphtheria and 94% were susceptible to tetanus. After one Td dose, 78% became fully immune to diphtheria, 13% attained basic immunity, and 9% were still susceptible to the disease. In contrast, 79% remained susceptible to tetanus, 4% had basic immunity and 17% were fully immune. Although one Td dose increases immunity to diphtheria in many elderly people who live in Brazil, a complete vaccination series appears to be necessary for the prevention of tetanus.

Immunity to diphtheria and tetanus in Australia: a national serosurvey

OBJECTIVE

To determine immunity to tetanus and diphtheria in the Australian population.

DESIGN AND SETTING

Analysis, using double antigen enzyme immunoassays, of a representative sample of sera (1950 samples tested for diphtheria and 2884 for tetanus) collected opportunistically from Australian laboratories between July 1996 and May 1999.

MAIN OUTCOME MEASURE

Immunity to diphtheria and tetanus, defined as negative (susceptible) when the antitoxin level was < 0.01 IU/mL, positive (immune) when it was > or = 0.1 IU/mL, and low positive (partially immune) when it was in the range 0.01-< 0.1 IU/mL.

RESULTS

About 99% of children aged 5-9 years had diphtheria and tetanus antitoxin levels > or = 0.01 IU/mL (immune or partially immune). Antitoxin levels declined with age and generally more markedly for diphtheria than tetanus. For subjects aged 50 years and over, less than 60% were immune or partially immune to diphtheria and less than 75% to tetanus. Men and women had similar diphtheria antitoxin levels, while women had lower levels of tetanus antitoxin compared with men of the same age, with the difference being most marked in the age group > or = 70 years (37% v 60%; P < 0.001).

CONCLUSIONS

Immunity in children appears to be good, but adults, especially older people, may not be adequately protected. Recent changes to the Australian Standard Vaccination Schedule should improve immunity in cohorts now aged < 50 years. However, additional efforts are required to protect those over 50 years (especially travellers), who are most susceptible.

Model selection methodology for inter-laboratory standardisation of antibody titres

The aim of the European Sero-Epidemiology Network 2 (ESEN2) is to compare standardised serological results of vaccine preventable diseases across Europe. In order to adjust for laboratory and assay differences, the participant laboratories tested a standardisation panel for each disease and the results were plotted against those of a reference centre in order to obtain standardisation equations. We describe an algorithm for obtaining these equations which took into account outliers, censored data and model selection, and needed to be robust due to the variety of assays and diseases under investigation. If the standardisation equations explained sufficient variability, these were used to convert each country's main serum bank results to a common unitage, thereby allowing international comparisons to be made.

Mucosal vaccination against diphtheria using starch microparticles as adjuvant for cross-reacting material (CRM197) of diphtheria toxin

Mucosal vaccination has the advantage of eliciting a local mucosal immune response as well as a systemic response. In this investigation, polyacryl starch microparticles were conjugated to diphtheria toxin cross-reacting material (CRM197) as a mucosal adjuvant for oral or intranasal immunisation of mice. Various methods of stabilising CRM197 with formaldehyde were investigated. A good systemic and local mucosal immune response was attained with oral immunisation when CRM197 was treated with a relatively low formaldehyde concentration prior to conjugation to the microparticles. No immune response was seen after intranasal immunisation.

Tetanus and diphtheria antibodies and response to a booster dose in Brazilian HIV-1-infected women

Tetanus and diphtheria (Td) antibodies were studied in HIV-1-infected women during puerperium. HIV group (n=61) was compared with Control group (n=101). Twenty-one women from HIV and 13 from Control group who had antibody levels lower than 0.1 IU/mL received a booster with Td vaccine. Antibodies were assessed by double antigen ELISA. Mean tetanus and diphtheria antibody levels from HIV group were lower than those from Control group. Multiple linear regression analysis showed that tetanus and diphtheria antibody levels were decreased by HIV-1-infection, and that was independent of the reduction due to the time interval between last booster and antibody assessment. After a booster dose, both groups had an increase in mean tetanus and diphtheria antibody levels, but in Control group the levels were higher than in HIV group.

Oral vaccination against diphtheria using polyacryl starch microparticles as adjuvant

Oral vaccination offers the advantage of eliciting both a mucosal and a systemic immune response. This study investigated the use of polyacryl starch microparticles as adjuvant for oral vaccination against diphtheria. Diphtheria toxin or cross-reacting material (CRM197) were covalently conjugated to the microparticles and fed to mice by oral gavage. Investigation of formaldehyde treatment as a means of either detoxifying (diphtheria toxin) or stabilising (CRM197) these formulations were also made. We show that all our formulations given orally or parenterally to mice induced a strong systemic immune response. Only formulations given orally induced a mucosal IgA-response. Furthermore, our formulations given parenterally or orally induced a strong diphtheria toxin-neutralising antibody response.

European Sero-Epidemiology Network: standardisation of the assay results for pertussis

A standardisation process was developed in order to compare and harmonize serological results of pertussis toxin (PT) antibody measurements performed by laboratories using different technical procedures for detection. This involved the development of a common panel, of sera by a designed reference centre, the distribution of the panel to each participating laboratory for testing with their routine methods, the comparison of the obtained results to those of the reference centre, and the calculation of standardisation equations by regressing the quantitative results against those of the reference centre. As a cut-off indicative of protection against pertussis has not yet been defined, a particular emphasis was laid upon achieving standardisation of high titre results that would allow epidemiological evaluations based on the estimation of the incidence of recent infections rather than on the traditional approach of determining the population immunity profile. A generally good agreement was achieved between the participating laboratories, all using ELISA procedures very similar in many crucial aspects, and standardisation equations were produced useful to enable inter-country comparison during the next stages of the European Sero-Epidemiology Network (ESEN) project concerning the serological surveillance of immunity to pertussis in Europe.

Evaluating acceptability and completeness of overseas immunization records of internationally adopted children

BACKGROUND

Increasing numbers of families in the United States are adopting children who were born in other countries. Appropriate immunization of internationally adopted children provides a challenge to pediatricians who must evaluate documentation of vaccines administered overseas and fulfill the recommended US childhood immunization schedule. The acceptability of vaccinations received outside the United States was addressed by the Advisory Committee on Immunization Practices in 1994, but few population-based studies assessing these vaccinations have been reported.

METHODS

We performed a retrospective cohort study of 504 children who were adopted from other countries and evaluated in 1997 and 1998. Our goal was to determine the acceptability of overseas vaccinations for meeting US immunization requirements. We assessed immunization records for both valid documentation of receipt of vaccine and comparability with the recommended US schedule. We also determined the number of children who were up to date (UTD) for diphtheria-tetanus-pertussis, polio, hepatitis B, and measles-mumps-rubella vaccines under the US schedule.

RESULTS

The children's mean age at initial US evaluation was 19 months; 71% were girls, and most (88%) had resided in orphanages. They were adopted from 16 countries, most frequently from China (48%) and Russia (31%). Thirty-five percent (178) of children had overseas immunization records, 167 (94%) of which were considered valid. Most children with valid records (112 [67%] of 167) were UTD for 1 or more vaccine series under the US schedule.

CONCLUSION

The majority (65%) of internationally adopted children had no written records of overseas immunizations. Among the 178 children with documented overseas immunizations, 167 (94%) had valid records and some vaccine doses that were acceptable and UTD under the US schedule. Additional research and more specific guidance in the most cost-effective approaches to evaluation of overseas vaccinations are needed to ensure appropriate state-side vaccination and to improve the health of these children and their communities.