Persistence of Anti-Hbs after up to 30 Years in Health Care Workers Vaccinated against Hepatitis B Virus

Evaluación serológica y vacuna para la hepatitis B entre Agentes Comunitarios de Salud

Resumen Objetivo: identificar la situación de la vacunación y serología contra la hepatitis B entre agentes comunitarios de la salud, vacunar contra el virus de la hepatitis B y evaluar la respuesta inmunológica de los agentes susceptibles. Método: fase I, estudio transversal y descriptivo, entre agentes comunitarios de la salud de una capital de la región centro oeste, por medio de cuestionario autoadministrado, verificación del carné de vacunación y extracción de sangre para comprobar los marcadores serológicos para la hepatitis B. Fase II, estudio de cohorte realizado en trabajadores vacunados no inmunes e identificados en la Fase I; estos recibieron una dosis de la vacuna (dosis de desafío) y realizaron el test serológico. Resultados: participaron del estudio 109 agentes. La mayoría tenía registro de vacunación (97; 89,0%) y de cobertura de vacunación (75; 77,3%); el marcador anti-HBs (Anticuerpos contra el virus de la hepatitis B) aislado fue detectado en 78 (71,6%) de los agentes. La prevalencia de exposición al virus de la hepatitis B fue de 8,2%. De los diez agentes vacunados no inmunes, después de la dosis desafío, uno permaneció susceptible. Conclusión: a pesar de que la mayoría de los trabajadores estaban vacunados y presentaron respuesta inmunológica para la hepatitis B, la susceptibilidad, después de la dosis desafío, fue identificada. Por tanto, es necesario que exista un programa de vigilancia de la situación de vacunación y estado serológico para este virus, para promover la seguridad de estos trabajadores.

Avaliação sorológica e vacinal para hepatite B entre Agentes Comunitários de Saúde

Resumo Objetivo: identificar a situação vacinal e sorológica contra hepatite B entre agentes comunitários de saúde; vacinar contra o vírus da hepatite B e avaliar a resposta imunológica dos agentes susceptíveis. Método: fase I, estudo transversal e descritivo, entre agentes comunitários de saúde de uma capital da região Centro-oeste, por meio de questionário autoaplicável, conferência do cartão vacinal e coleta de sangue para testagem dos marcadores sorológicos para hepatite B. Fase II, estudo de coorte realizado em trabalhadores vacinados não imunes e identificados na fase I. Estes receberam uma dose da vacina (dose desafio) e teste sorológico. Resultados: participaram do estudo 109 agentes. A maioria tinha registro de vacinação (97; 89,0%) e completude vacinal (75; 77,3%), já o marcador anti-HBs (anticorpos contra o vírus da hepatite B) isolado foi detectado em 78 (71,6%) agentes. A prevalência de exposição ao vírus da hepatite B foi de 8,2%. Dos dez agentes vacinados não imunes, após a dose desafio, um permaneceu susceptível. Conclusão: apesar da maioria dos trabalhadores estarem vacinados e apresentarem resposta imunológica para hepatite B, a suscetibilidade após a dose desafio foi identificada. Portanto, é necessário que haja um programa de vigilância da situação vacinal e estado sorológico para este vírus, para promover a segurança destes trabalhadores.

Impaired humoral immune response to hepatitis B vaccine in patients on maintenance hemodialysis

Hepatitis B virus (HBV) infection is a worldwide health problem. We aimed in this study to investigate the humoral immune response derived to HBV vaccine following completing the vaccine series in Madinah. Two hundred and two Saudi hemodialysis (HD) patients were included in this cross-sectional study. Mean concentration of Hepatitis B surface antibody (anti-HBs) was significantly higher among patients who received the vaccination twice compared to patients who received the vaccination only after starting hemodialysis (252 ± 489 mIU/mL vs. 144 ± 327 mIU/mL, respectively, p = 0.008). Almost half of the study sample were non-protected and showed anti-HBs concentration < 10 mlU/mL. In contrast, 20.3% (n = 41) were identified as poor responders (10-100 mlU/mL) and only 28.2% (n = 57) were identified as good responders (10-100 mlU/mL). However, the latter two groups were accounted as protected (48.5%, n = 98). Patients sex was associated with anti-HBs concentration (non-responders; poor responders; good responders), where significantly higher proportion of good responders were females compared to males (p = 0.007). In conclusion, HBV vaccine is efficient to elicit humoral immune response in hemodialysis patients.

The persistence of seroprotective levels of antibodies after vaccination with PreHevbrio, a 3-antigen hepatitis B vaccine

Prevention of hepatitis B virus (HBV) infection by vaccination can potentially eliminate HBV-related diseases. PreHevbrio™/PreHevbri® is a 3-antigen (S, preS1, preS2) HBV vaccine (3A-HBV) recently licensed for adults in the US, EU and Canada. This study evaluated antibody persistence in a subset of fully vaccinated and seroprotected (anti-HBs ≥ 10 mIU/mL) Finnish participants from the phase 3 trial (PROTECT) of 3A-HBV versus single-antigen HBV vaccine (1A-HBV). 465/528 eligible subjects were enrolled (3A-HBV: 244; 1A-HBV: 221). Baseline characteristics were balanced. After 2.5 years, more 3A-HBV subjects remained seroprotected (88.1 % [95 %CI: 84.1,92.2]) versus 1A-HBV (72.4 % [95 %CI: 66.6,78.3)], p < 0.0001) and had higher mean anti-HBs [1382.9 mIU/mL (95 %CI: 1013.8,1751.9) versus 252.6 mIU/mL (95 %CI: 127.5,377.6), p < 0.0001]. In multiple variable logistic regression analysis including age, vaccine, initial vaccine response, sex and BMI, only higher post dose 3 (Day 196) antibody titers significantly reduced the odds of losing seroprotection.

ABO blood types, but not Secretor or Lewis blood types, influence strength of antibody response to Hepatitis B vaccine in Black South African children

Subunit vaccines for the Hepatitis B virus (HBV) have greatly reduced the prevalence of infection and morbidity through HBV-related liver cirrhosis and cancer. However, strength of immune response to vaccination varies considerably. While it is known that ABO blood types may influence HBV infection risk, the role of ABO and related blood types in strength of immune response to HBV vaccine has not been investigated. We examined 16 polymorphisms in the ABO, FUT2, and FUT3 genes and their related phenotypes for associations with strength of antibody response to HBV vaccine in Black South African infants. Anti-HBc and anti-HBs antibody levels were measured by CMIA assay 1-3 months after the last dose of HBV vaccine. Prior infection occurred in 8/207 individuals (3.86%) who were removed from further study. Of the remaining 199 individuals, 83.4% individuals were strong responders (anti-HBs ≥ 100 mIU/ml, median 973 mIU/ml), another 15.6% were weak responders (anti-HBs < 100 mIU/ml, median 50 mIU/ml) and 1% were non-responders (anti-HBs < 10 mIU/ml). The frequency of weak responders to HBV vaccine was not significantly affected by sex, birthweight, use of an additional booster dose of vaccine or cohort of origin. We characterised patterns of genetic variation present at the ABO, FUT2 and FUT3 loci by use of MassArray genotyping and used these data to predict ABO, Secretor and Lewis phenotypes. We observed significant association of ABO blood type with strength of antibody response to HBV vaccine in a Black South African cohort (p = 0.002). In particular, presence of rs8176747G and expression of B antigen (whether in B blood type or AB blood type) was associated with decreased antibody response to HBV vaccine. Secretor and Lewis blood types were not associated with antibody response to HBV vaccine. This work increases our understanding of the impact that host genetic variation may have on vaccine immunogenicity.

Prevalence, Risk Factors and Vaccine Response against Hepatitis B in People Aged 50 Years or Older

Universal immunization against hepatitis B has contributed to reducing incidence of the disease, but older individuals remain susceptible to acquiring the hepatitis B virus worldwide. Thus, this study aimed to investigate the epidemiology of HBV infection in individuals aged 50 years and over in central Brazil and to evaluate the immunogenicity of the monovalent vaccine against hepatitis B in this age group using two vaccine regimens. Method: Initially, a cross-sectional and analytical study was carried out to investigate the epidemiology of hepatitis B. Then, individuals without proof of vaccination for hepatitis B were recruited for a phase IV randomized and controlled clinical trial using two vaccine regimens: Intervention Regimen (IR) (three doses of 40 μg at months 0, 1 and 6) vs. Comparison Regimen (CR) (three doses of 20 μg at months 0, 1 and 6). Results: The overall prevalence of exposure to HBV was 16.6% (95% CI: 14.0%–9.5%). In the clinical trial, statistical differences in protective titers were observed (p = 0.007; IR 96% vs. CR 86%) and the geometric mean of anti-HBs titers was higher in individuals who received the IR (518.2 mIU/mL vs. 260.2 mIU/mL). In addition, the proportion of high responders was higher among those who received the IR (65.3%). Conclusion: reinforced doses should be used in individuals aged 50 years or older to overcome the lower efficacy of the vaccine against hepatitis B.

Hepatitis B burden and population immunity in a high endemicity city - a geographically random household epidemiology study for evaluating achievability of elimination

This study aimed to provide reference for evaluating the achievability of hepatitis B virus (HBV) elimination in a high endemicity city with universal neonatal vaccination in place for over 30 years. Between September 2018 and October 2020, 2085 citizens from 1143 geographically random households in Hong Kong completed a questionnaire and had blood-testing for HBV markers (anti-HBs, HBsAg, anti-HBc, HBeAg). We evaluated the epidemiology and examined factors associated with HBV exposure, vaccination and chronic diseases. The proportion of households with HBsAg positive index participants was 9.2% (95% CI 7.5%-10.9%). The age- and sex-adjusted HBsAg prevalence was 6.3% (95% CI 5.3%-7.4%), compared to >10% in those born in 1960-1970 and among non-local born citizens, and <1% in people born after introduction of neonatal vaccination. Among 155 HBsAg positive participants, 59% were aware of their infection status with 10% on treatment and 10/150 (6.7%) HBeAg positive. More than 40% (872/2064) tested negative for both HBsAg and anti-HBs, contributed by the lack of immunity in older adults and the waning immunity of vaccines. Hong Kong has remained at high-intermediate HBV endemicity state. The moderate level of anti-HBs positivity and very low treatment coverage (10%) among HBsAg positive participants pose challenges for achieving the HBV elimination target.

Serological and vaccine evaluation for hepatitis B among Community Health Workers

OBJECTIVE

to identify the vaccination and serological status against hepatitis B among community health workers; to vaccinate against hepatitis B virus and to evaluate the immune response of susceptible workers.

METHOD

phase I, cross-sectional and descriptive study, among community health workers in a capital city of the Midwest region, through a self-administered questionnaire, checking of vaccination cards, and blood collection for testing of serological markers for hepatitis B. Phase II, cohort study carried out in vaccinated non-immune workers identified in phase I. They received one dose of vaccine (challenge dose) and serological testing.

RESULTS

a total of 109 workers participated in the study. Most had vaccination record (97; 89.0%) and vaccination completeness (75; 77.3%), while the isolated anti-HBs (Antibodies against hepatitis B virus) marker was detected in 78 (71.6%) workers. The prevalence of hepatitis B virus exposure was 8.2%. Of the ten non-immune vaccinated workers, after challenge dose, one remained susceptible.

CONCLUSION

although most workers are vaccinated and show immunological response to hepatitis B, susceptibility after challenge dose was identified. Therefore, it is necessary to have a surveillance program of the vaccination situation and serological status for this virus, to promote these workers' safety.

Protection and antibody levels 35 years after primary series with hepatitis B vaccine and response to a booster dose

BACKGROUND AND AIMS

The duration of protection from hepatitis B vaccination in children and adults is not known. In 1981, we used three doses of plasma-derived hepatitis B vaccine to immunize a cohort of 1578 Alaska Native adults and children from 15 Alaska communities who were ≥6 months old.

APPROACH AND RESULTS

We tested persons for antibody to hepatitis B surface antigen (anti-HBs) levels 35 years after receiving the primary series. Those with levels <10 mIU/ml received one booster dose of recombinant hepatitis B vaccine 2-4 weeks later and were then evaluated on the basis of anti-HBs measurements 30 days postbooster. Among the 320 recruited, 112 persons had not participated in the 22- or 30-year follow-up study (group 1), and 208 persons had participated but were not given an HBV booster dose (group 2). Among the 112 persons in group 1 who responded to the original primary series, 53 (47.3%) had an anti-HBs level ≥10 mIU/ml. Among group 1, 73.7% (28 of 38) of persons available for a booster dose responded to it with an anti-HBs level ≥10 mIU/ml at 30 days. Initial anti-HBs level after the primary series was correlated with higher anti-HBs levels at 35 years. Among 8 persons who tested positive for antibody to hepatitis B core antigen, none tested positive for HBsAg or HBV DNA.

CONCLUSIONS

Based on anti-HBs level ≥10 mIU/ml at 35 years and a 73.7% booster dose response, we estimate that 86% of participants had evidence of protection 35 years later. Booster doses are not needed in the general population at this time.

An Evidence-based Practical Guide to Vaccination for Hepatitis B Virus

The hepatitis B virus (HBV) is highly infectious, with over 292 million chronically infected people worldwide and up to 2.4 million in the United States. Following infection, clinically silent liver damage can ensue, but symptoms or signs of advanced disease, including cirrhosis and hepatocellular carcinoma, can take decades to emerge. HBV has the heaviest public health burden of all hepatitis viruses and has now surpassed other major communicable diseases (eg, HIV, diarrheal disease, malaria, tuberculosis) as a leading cause of death globally. Preventing transmission is essential, and efforts are in place to reinforce screening, vaccination, and routine follow-up. Three safe and effective vaccines are available in the United States and other countries for HBV prevention, and the benefits of vaccination in preventing infection and its sequelae have been substantiated. For the first time in over 25 years, a new Food and Drug Administration-approved vaccine is available that offers a high degree of immunogenicity after 2, rather than 3, injections. Persistent challenges include the underutilization of vaccination, choice of vaccine, incomplete vaccinations, varying needs in different populations, management of nonresponders or those with undocumented or incompletely documented vaccination courses, and questions about whether and when booster injections may be needed. A panel of US academic hepatologists with expertise and experience in preventing and managing HBV infection have collaborated to write this practical clinical paper intended to guide clinicians in vaccinating for HBV and address questions that regularly arise in the clinic.

Association between history of HBV vaccine response and anti-SARS-CoV-2 spike antibody response to the BioNTech/Pfizer's BNT162b2 mRNA SARS-CoV-2 vaccine among healthcare workers in Japan: A prospective observational study

INTRODUCTION

Inadequate vaccine response is a common concern among healthcare workers at the frontlines of the COVID-19 pandemic. We aimed to investigate if healthcare workers with history of weak immune response to HBV vaccination are more likely to have weak responses against the BioNTech/Pfizer's BNT162b2 mRNA SARS-CoV-2 vaccine.

METHODS

We prospectively tested 954 healthcare workers for the Anti-SARS-CoV-2 spike (S) protein antibody titers prior to the first and second BNT162b2 vaccination doses and after four weeks after the second dose using Roche's Elecsys® assay. We calculated the percentage of patients who seroconverted after the first and second doses. We estimated the relative risk of non-seroconversion after the first BNT162b2 vaccine (defined as anti-SARS-CoV-2-S titer <15 U/mL) among HBV vaccine non-responders (HBs-Ab titer <10 mIU/mL) and weak responders (≥10 and <100 mIU/mL) compared to normal responders (≥100 mIU/mL).

RESULTS

Among 954 healthcare workers recruited between March 9 and March 24, 2021 at Osaka Medical and Pharmaceutical University, weak and normal HBV vaccine responders had comparable S-protein titers after the first BNT162b2 dose (51.4 [95% confidence interval 25.2-137.0] versus 59.7 [29.8-138.0] U/mL, respectively). HBV vaccine non-responders were more likely than normal responders to not seroconvert after a single dose (age and sex-adjusted relative risk 1.85 95% confidence interval [1.10-3.13]) although nearly all participants seroconverted after the second dose. After limiting the analysis to 382 patients with baseline comorbidity data, the comorbidity-adjusted relative risk of non-seroconversion among HBV vaccine non-responders to normal responders was 1.32 (95% confidence interval [0.59-2.98]).

DISCUSSION

Long term follow-up studies are needed to understand if protective immunity against SARS-CoV-2 wanes faster among those with history of HBV vaccine non-response and when booster doses are warranted for these healthcare workers.

Antibody levels and protection after Hepatitis B vaccine in adult vaccinated healthcare workers in northern Uganda

Hepatitis B vaccine has contributed to the reduction in hepatitis B virus infections and chronic disease globally. Screening to establish extent of vaccine induced immune response and provision of booster dose are limited in most low-and-middle income countries (LMICs). Our study investigated the extent of protective immune response and breakthrough hepatitis B virus infections among adult vaccinated healthcare workers in selected health facilities in northern Uganda. A cross-sectional study was conducted among 300 randomly selected adult hepatitis B vaccinated healthcare workers in Lira and Gulu regional referral hospitals in northern Uganda. Blood samples were collected and qualitative analysis of Hepatitis B surface antigen (HBsAg), Hepatitis B surface antigen antibody (HBsAb), Hepatitis B envelop antigen (HBeAg), Hepatitis B envelop antibody (HBeAb) and Hepatitis B core antibody (HBcAb) conducted using ELISA method. Quantitative assessment of anti-hepatitis B antibody (anti-HBs) levels was done using COBAS immunoassay analyzer. Multiple logistic regression was done to establish factors associated with protective anti-HBs levels (≥ 10mIU/mL) among adult vaccinate healthcare workers at 95% level of significance. A high proportion, 81.3% (244/300) of the study participants completed all three hepatitis B vaccine dose schedules. Two (0.7%, 2/300) of the study participants had active hepatitis B virus infection. Of the 300 study participants, 2.3% (7/300) had positive HBsAg; 88.7% (266/300) had detectable HBsAb; 2.3% (7/300) had positive HBeAg; 4% (12/300) had positive HBeAb and 17.7% (53/300) had positive HBcAb. Majority, 83% (249/300) had a protective hepatitis B antibody levels (≥10mIU/mL). Hepatitis B vaccine provides protective immunity against hepatitis B virus infection regardless of whether one gets a booster dose or not. Protective immune response persisted for over ten years following hepatitis B vaccination among the healthcare workers.

Anti-HBs titers are not decreased after treatment with oral Cladribine in patients with Multiple Sclerosis vaccinated against Hepatitis B virus

BACKGROUND

Oral cladribine is a novel treatment for Multiple Sclerosis (MS). It is a purine nucleoside antimetabolite analogue that is incorporated into the DNA, resulting in single-strand breaks in DNA and apoptosis of replicating lymphocytes. Specifically, Cladribine induces limited depletion of CD4 and CD8 T cell subsets and more marked depletion of memory B cell subsets. Therefore, natural and acquired humoral responses against pathogens may be potentially reduced. The aim of this study was to assess longitudinal variation of antiHBs titers in patients with MS treated with Cladribine.

METHODS

Patients with MS treated with 1 cycle of Cladribine (3,5 mg/kg) and previously vaccinated against Hepatitis B virus (HBV) were enrolled. Anti-HBs titers were compared before and after 12 months from Cladribine treatment. Total lymphocyte count was also analysed.

RESULTS

Among the 13 RMS patients (10 F, 3 M, mean age 33,8, SD 5,9) enrolled, all had anti-HBs titers >10 mg/dl at baseline. Anti-HBs titer dropped below the reference value at 12 months after Cladribine only in 1 case. Pre-post Cladribine mean anti-HBs values were not significantly different considering the whole cohort (Wilcoxon-Mann-Whitney Test p = 0,762). Four patients had grade 1 and 1 patient grade 2 lymphocytopenia at 12 months.

CONCLUSIONS

Cladribine does not seem to reduce humoral immune responses in subjects previously vaccinated against HBV, even in case of lymphocytopenia. These results, if confirmed in larger populations, appear reassuring also for other vaccinations (i.e. COVID19). The low impact of Cladribine on plasma cells may explain such findings.

Screening of Hepatitis A and B Seropositivity among Turkish Healthcare Providers Admitted to Occupational Health Services

This study aimed to determine the protection rates against hepatitis A virus (HAV) and hepatitis B virus (HBV), among healthcare providers (HCPs). The occupational health service data of Gaziosmanpaşa Training and Research Hospital between January 2020 and December 2020 were evaluated for this retrospective observational study. Of the 1,722 participants aged 34.40 ± 9.16 years, 48.6% (n = 861) were male, and 55.0% (n = 975) were doctors and nurses. The anti-HBs seropositivity rate was 87.5% (n = 1,501). None of the participants had anti-HCV antibodies. Twelve participants were HBsAg positive. A level of anti-HBs titer ≥10 mIU/mL was maintained in 66.7% of the HCPs vaccinated in childhood, while 71.3% (n = 1,263) of the participants had anti-HAV IgG. HAV vaccination needs were higher in the doctor and nurse groups than in the other groups (60.5% and 39.5%, respectively, p = 0.003). HBV protection was higher among HCPs in polyclinics/wards and surgery/intensive care units than in those working in the emergency department (odds ratio (OR): 2.099, 95% confidence interval (CI) = 1.285-3.429; OR: 1.592, 95% CI = 1.037-2.443, respectively). HAV protection was higher in HCPs aged 31-50 years and over 50 years than in those aged 18-30 years (OR: 2.046, 95% CI = 1.647-2.541; OR: 3.615, 95% CI = 2.164-6.037, respectively). In this study, one out of every two HCPs aged 18-30 years admitted to the occupational health control services had not yet received the HAV vaccine. The low levels of HBV protection among HCPs in the emergency department highlight the need for occupational health screening and HBV vaccination for HCPs working in emergency services in hospitals.

Undetectable Anti-HBs Antibodies: Need of a Booster Dose for HIV-1-Infected Individuals

HBV vaccination effectively prevents HBV transmission and the development of liver cancer. Disease progression and liver-related complications are more common in HIV-1/HBV co-infected than HBV mono-infected individuals. A considerable body of literature, which will be reviewed here, indicates that response to HBV vaccine is suboptimal in HIV-1-infected individuals and that the poor maintenance of protective immunity to HBV vaccines in these individuals is an important medical issue. Several factors affect HBV vaccine response during HIV-1 infection including CD4+ T cell counts, B cell response, vaccine formulation, schedules, and timing of antiretroviral therapy (ART). The initial response to HBV vaccination also plays a critical role in the sustainability of antibody responses in both HIV-1-infected and uninfected vaccinees. Thus, regular follow-up for antibody titer and a booster dose is warranted to prevent HBV transmission in HIV-1 infected people.

12 Months Persistent Immunogenicity after Hepatitis B Vaccination in Patients with Type 2 Diabetes and Immunogenicity of Revaccination in Non-Responders: An Open-Label Randomized Controlled Trial

BACKGROUND

In initial studies, the immunogenicity and safety of hepatitis B vaccines in patients with diabetes has been assessed in China.

METHODS

In six township health centers in Gansu Province, 232 diabetic patients and 77 healthy people were allocated to receive two 3-dose hepatitis B vaccines (Group D20SC 0-1-6; Group D20CHO 0-1-6; Group ND20SC 0-1-6). Participants were followed up at 12 months after being fully vaccinated. One dose of the vaccine was randomly administered to non-responders. Chi-square test was used to compare the differences in response rate between two groups.

RESULTS

The anti-HBs response rates of three groups decreased from 84.1%, 89.1% and 88.3% at one month to 64.6%, 79.8% and 71.4% at twelve months. There was no statistical difference in the immune response rates between Group D20SC 0-1-6 and Group ND20SC 0-1-6; however, that of Group D20CHO 0-1-6 was higher than that of Group D20SC 0-1-6. After revaccination, the geometric mean concentrations were 491.7 mIU/mL and 29.7 mIU/mL after using vaccines containing 60 μg and 20 μg HBsAg.

CONCLUSIONS

At 12 months, immune response in diabetic patients were not significantly different from that in healthy people. Revaccination with one dose of hepatitis B vaccine containing 60 μg HBsAg for non-responders was more satisfactory.

Future Healthcare Workers and Hepatitis B Vaccination: A New Generation

Before the introduction of universal vaccination, hepatitis B caused high morbidity and mortality, especially among healthcare workers. In the present study, the immune status against hepatitis B was assessed in a cohort of 11,188 students of the degree courses of the School of Medicine of the University of Padua (Italy) who had been subjected to mandatory vaccination in childhood or adolescence and who will be future healthcare workers. The variables that influence the antibody response to vaccination are mainly the age at which the vaccine was administered and sex. If vaccination was administered before one year of age, there is a high probability (around 50%) of having an antibody titer lower than 10 IU/L compared to those vaccinated after one year of age (12.8%). The time between vaccine and analysis is not decisive. Furthermore, female sex, but only if vaccination was administered after one year of age, shows a significant (p = 0.0008) lower percentage of anti-HBs below 10 IU/L and a greater antibody titer (p < 0.0001). In conclusion, the differences related to the age of vaccination induce more doubts than answers. The only plausible hypothesis, in addition to the different immune responses (innate and adaptive), is the type of vaccine. This is not easy to verify because vaccination certificates rarely report it.