Immune memory to hepatitis B persists in children aged 7-8 years, who were vaccinated in infancy with 4 doses of hexavalent DTPa-HBV-IPV/Hib (Infanrix™ hexa) vaccine

A worldwide overview for hexavalent vaccines and a glimpse into Turkiye's perspective

The surge in recommended vaccinations for child's has spurred the development of combination vaccines, notably hexavalent vaccines, which provide multiple immunizations in a single dose. These vaccines offer various advantages, such as streamlining vaccination schedules, minimizing injection-related pain and exposure to preservatives, expanding vaccine coverage, and reducing administration costs. However, the intricate and expensive development of these vaccines presents substantial challenges, requiring increased investment and healthcare provider education to optimize their utilization and sustain high vaccination rates. Turkey, known for its robust vaccine coverage, strategic geographic location, and the influx of refugees, is at a critical juncture for integrating hexavalent vaccines into national programs. This transition is especially relevant given the rising vaccine hesitancy and the potential resurgence of vaccine-preventable diseases. This review assesses the deployment of hexavalent vaccines, examining their benefits and challenges through clinical trials and global experiences, with a specific emphasis on Turkiye's public health context.

Persistence of hepatitis B surface antibody until 7 years of age following administration of hexavalent and pentavalent vaccines in children at 2, 4, 6, and 18 months

Thailand incorporated the hepatitis B (HepB) vaccine into the infant combination vaccine known as pentavalent wP-containing vaccines (DTwP-HB-Hib) and hexavalent aP-containing vaccines (DTaP-IPV-HB-Hib). We followed healthy children from the clinical trial (ClinicalTrials.gov NCT02408926) in which children were randomly assigned to receive either pentavalent or hexavalent vaccines for their primary series (administered at 2, 4, and 6 months) and first booster vaccination (at 18 months), following the monovalent HepB vaccine at birth. Blood samples were collected to evaluate the persistence of hepatitis B surface antibody (anti-HBs) at 3, 4, 5, 6 and 7 years of age. The results showed that at 7 years of age, a higher percentage of children in the hexavalent group maintained anti-HBs levels ≥ 10 mIU/mL compared to those in the pentavalent group (86.9 % vs. 59.7 %). This study showed good persistence of anti-HBs among hexavalent-vaccinated children 5.5 years after the last dose of the HepB vaccine.

Demonstration of durable hepatitis B immune memory in children vaccinated with a DTaP5-IPV-HepB-Hib infant-toddler series 7 to 8 years previously

Vaccination against hepatitis B (HepB) provides long-term protection against infection. This is despite a reduction in HepB surface antibody (anti-HBs) concentrations over time to levels below the well-accepted correlate of protection of ≥10 mIU/mL. Continued evidence of immune memory and protection despite declined anti-HBs concentrations can be demonstrated by HepB virus surface antigen challenge studies. Long-term immune memory and protection against HepB infection has not been demonstrated previously for the pediatric hexavalent vaccine DTaP5-IPV-HepB-Hib. This phase 3, multicenter, single-group, open-label challenge study (NCT04490499; EudraCT: 2020-000126-26) evaluated immune memory against HepB infection in children who had received DTaP5-IPV-HepB-Hib at 2, 4, and 11-12 months of age, or at 2, 3, 4, and 12 months of age. At age 8-9 years, they were each challenged with 5 μg of monovalent HepB vaccine. Anti-HBs levels were measured on pre-challenge day 1 and post-challenge day 30. At baseline, 45.4% (93 of 205) had anti-HBs levels ≥10 mIU/mL. On post-challenge day 30, 99.5% (201 of 202) had anti-HBs levels ≥10 mIU/mL, regardless of initial vaccination schedule. Post-challenge, geometric mean concentrations increased 71-fold over baseline and 96.0% of children had a ≥4-fold rise in anti-HBs concentrations with similar results across both dosing schedules. The challenge dose was well tolerated. The robust anti-HBs responses after a single 5-μg dose of HepB vaccine confirm the persistence of a HepB immune memory and demonstrate that DTaP5-IPV-HepB-Hib provides long-term protection against HepB.

Immunogenicity and Safety of Childhood Combination Vaccines: A Systematic Review and Meta-Analysis

Background: Vaccination is considered the most effective and economical measure for controlling infectious diseases. Although combination vaccines are widely used worldwide, whether any of the combination vaccines is superior to each separate vaccine has yet to be established. This systematic review and meta-analysis aimed to summarize the available evidence on the effectiveness and safety of combination vaccines in children. Methods: A systematic search was conducted from database inception to August 20, 2021, in MEDLINE, Embase, Cochrane, and Scopus. Published randomized clinical trials (RCTs) and open-label trials of immunogenicity and safety of combined vaccines were selected. The results of the studies were quantitatively synthesized. Results: Overall, 25 articles met the inclusion criteria and were included in the meta-analysis. The results indicated that the combined diptheria−tetanus−acellular pertussis (DTaP)−hepatitis B virus (HBV)−Haemophilus influenzae type B (Hib) vaccine group had lower levels of anti-tetanus antibodies than the combined DTaP−HBV and separate Hib vaccinations group (SMD = −0.23; 95% CI: −0.42, −0.05; p = 0.013). Meanwhile, the combined DTaP−HBV−inactivated polio virus (IPV)−Hib vaccine group had higher levels of anti-pertussis (PT) and anti-filamentous hemagglutinin (FHA) antibodies than the combined DTaP−IPV−Hib and separate HBV vaccinations group (anti-PT: SMD = 0.60; 95% CI: 0.45, 0.75; p < 0.0001; anti-FHA: SMD = 0.40; 95% CI: 0.01, 0.78; p = 0.042). The levels of anti-pertactin (PRN) antibodies were lower in the combined DTaP−IPV−Hib vaccine group than in the combined DTaP−IPV and separate Hib vaccinations group (SMD = −0.13; 95% CI: −0.27, −0.00; p = 0.047). The individuals injected with the DTaP−HBV−IPV−Hib vaccine had a lower risk of pain and swelling than those injected with the combined DTaP−HBV−IPV and separate Hib vaccines (pain: RR = 0.79; 95% CI: 0.69, 0.91; p = 0.001; swelling: RR = 0.87; 95% CI: 0.78, 0.98; p = 0.020). However, the group that received the DTaP−HBV−IPV−Hib vaccine had a higher risk of fever than the group that received DTaP−HBV−IPV and separate Hib vaccinations (RR = 1.13; 95% CI: 1.02, 1.26; p = 0.021). Conclusions: This meta-analysis suggests that the combined vaccines (DTaP−IPV−Hib, DTaP−HBV−Hib, DTaP−HBV−IPV−Hib) are safe, well-tolerated, and provide immunogenic alternatives to separate vaccines in children. The combined DTaP−HBV−IPV−Hib vaccine showed a higher incidence of fever, which was lower than the cumulative incidence of fever induced by all vaccines. Future studies should evaluate the cost-effectiveness of using combined vaccines and compare the potency of different formulations to improve routine local or national childhood immunization programs.

Hexavalent vaccines: What can we learn from head-to-head studies?

BACKGROUND

Three hexavalent vaccines against diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B virus (HBV), and Haemophilus influenzae type b (Hib) are licensed in Europe: Infanrix hexa (DT3aP-HBV-IPV/Hib), Hexyon (DT2aP-HBV-IPV-Hib) and Vaxelis (DT5aP-HBV-IPV-Hib).

METHODS

A systematic literature search was performed in various electronic databases to identify published peer-reviewed head-to-head studies comparing any licensed hexavalent vaccine to another.

RESULTS

Predefined inclusion criteria were met by 12 articles. Individual studies concluded that the 3 hexavalent vaccines have acceptable safety profiles although some significant differences were observed in their reactogenicity profiles. The immunogenicity of DT2aP-HBV-IPV-Hib and DT5aP-HBV-IPV-Hib was non-inferior versus DT3aP-HBV-IPV/Hib. Some differences in immune responses to common antigens were observed, but their clinical relevance was not established. Anti-filamentous hemagglutinin (FHA) from pertussis and anti-polyribosylribitol phosphate (PRP) from Hib antibody concentrations tended to be higher, and anti-HBV and anti-pertussis toxin (PT) from pertussis antibody concentrations lower in DT2aP-HBV-IPV-Hib versus DT3aP-HBV-IPV/Hib vaccinees. Anti-PT and post-primary anti-PRP antibody concentrations tended to be higher, and anti-HBV, anti-FHA, anti-pertactin from pertussis and post-booster anti-PRP antibody concentrations lower in DT5aP-HBV-IPV-Hib versus DT3aP-HBV-IPV/Hib recipients. Slightly lower immune responses towards most vaccine antigens were observed with 2 + 1 versus 3 + 1 schedules post-primary vaccination, suggesting that 2 + 1 schedules should only be considered in countries with very high vaccination coverage.

CONCLUSION

Although the licensed hexavalent vaccines are generally considered similar, analyses of immunogenicity data from head-to-head trials highlighted differences that could be related to differences in composition and formulation. In addition, the demonstrated non-inferiority of the immunogenicity of the more recent vaccines versus DT3aP-HBV-IPV/Hib does not allow a full bridging to similar efficacy, effectiveness and safety. The availability of DT3aP-HBV-IPV/Hib over > 20 years allowed to collect a wealth of data on its long-term immunogenicity, safety and effectiveness in clinical and post-marketing studies, and makes it a key pillar of pediatric immunization.

Variable anti-HBs antibody titers in vaccinated birth cohorts - A cross-sectional population-based study

BACKGROUND

After the introduction of hepatitis B (HB) vaccination in 1995 in newborns, two catch-up campaigns targeted unvaccinated 9 year old in 2000-2003 (born 1991-1994) and the 18 year old in 2004-2008 (born 1986-1990), resulting in several birth-cohorts. Our objective was to assess the anti-HBs titers in each birth-cohort.

METHODS

We included all outpatients (78.5%) and hospitalized patients with measured anti-HBs antibody titers in the Teaching Hospital of Infectious Diseases, Cluj-Napoca, Romania, during April 2014 - December 2018 (without HB history). We compared the anti-HBs titers in all birth-cohorts using the Lexis surfaces (titers by age, time period and cohort patterns). We also evaluated the number of acute HB in the corresponding inpatient birth-cohorts and special groups.

RESULTS

We included 2963 participants, mean age = 31.0 ± 14.2, 64.1% women. The birth-cohort 1995-2006, vaccinated after delivery (n = 424, 3-dose HB vaccine coverage > 90%), had significantly lower protective titers (41.3% >10 mIU/mL) compared to the other birth-cohorts: born after 2007 (also vaccinated at birth, 67.0%, n = 106), 1991-1994 (age 9, 74.3%, n = 847), 1986-1990 (age 18, 71.3%, n = 543). In the unvaccinated cohort (n = 1043, mean age = 45.5 ± 12.4) protective titers were found in 44.8%, probably after self-limited HB infection. Concordant results were found using the proportion of patients with detectable or robust titers, and median or geometric mean titers. Four breakthrough acute HB infections were hospitalized of the corresponding vaccinated cohorts (birth years 1988, 1990, 1995, 1996). Data on a few tested infants (n = 47, not included in the main study) demonstrated good protection, 88.9%.

CONCLUSIONS

Our study demonstrated the long-term evidence of protection of HBV vaccine at two decades following the primary immunization and a booster seems unsupported. Further studies should be done to assess the need of a booster dose within the general population and special groups.

Antibody persistence in pre-school children after hexavalent vaccine infant primary and booster administration

Objective: Antibody persistence evaluation for all antigens of a fully liquid DTaP-IPV-HB-PRP~T vaccine at 3.5 and 4.5 y of age following different primary series and booster schedules in South Africa and Latin America.

Methods: Participants had completed one of two previous studies (Study 1-South Africa; Study 2-Latin America). In Study 1, participants who had not received HB vaccine at birth received a 6–10-14 week primary series of DTaP-IPV-HB-PRP~T or DTwP/PRP~T-Hib+HB+OPV and a third group who had received HB vaccine at birth received a 6–10-14 week primary series of DTaP-IPV-HB-PRP~T; all received a booster (15–18 months) of the primary series vaccine(s) except for HB in the DTwP/PRP~T-Hib group. In Study 2, participants received HB vaccine at birth, a 2–4-6 month primary series of DTaP-IPV-HB-PRP~T or DTaP-HB-IPV//PRP~T, and a DTaP-IPV-HB-PRP~T or DTaP-HB-IPV//PRP~T booster (12–24 months). Participants were followed up at 3.5 and 4.5 y of age for antibody persistence.

Results: Approximately 80% of eligible participants were assessed. In Study 1, a birth dose of HB increased anti-HBs persistence (≥10 mIU/mL) following DTaP-IPV-HB-PRP~T primary and booster vaccination from 76.3% to 96.1% at 3.5 y of age and from 73.3% to 96.1% at 4.5 y of age; in Study 2, anti-HBs persistence was high and similar in each group. For the other antigens, there were no differences between groups or studies at 3.5 or 4.5 y.

Conclusion: Good persistence of antibodies to each antigen in the DTaP-IPV-HB-PRP~T vaccine up to pre-school age, irrespective of the vaccination schedule during the first 2 y of life.

Long-term antibody persistence against hepatitis B in adolescents 14-15-years of age vaccinated with 4 doses of hexavalent DTPa-HBV-IPV/Hib vaccine in infancy

We evaluated antibody persistence against hepatitis B virus (HBV) in adolescents previously vaccinated with a hexavalent diphtheria-tetanus-acellular pertussis-HBV-inactivated poliovirus-Haemophilus influenzae type b conjugate vaccine (DTPa-HBV-IPV/Hib), as part of the national newborn immunization program in Germany. We also assessed the anamnestic response to a challenge dose of a monovalent HBV vaccine. In this phase 4, open-label, non-randomized study (NCT02798952), 302 adolescents aged 14-15 years, primed in their first 2 years of life with 4 DTPa-HBV-IPV/Hib doses, received one challenge dose of monovalent HBV vaccine. Blood samples were taken before and one month post-vaccination and used to determine antibody levels against hepatitis B surface antigen (HBs). Reactogenicity and safety were also assessed post-challenge dose. Pre-challenge dose, 53.7% of 268 participants included in the according-to-protocol cohort for immunogenicity had anti-HBs antibody concentrations ≥10 mIU/mL (seroprotection cut-off) and 16.8% had anti-HBs antibody concentrations ≥100 mIU/mL. One month post-challenge dose, 93.3% of adolescents had anti-HBs antibody concentrations ≥10 mIU/mL and 87.3% had antibody concentrations ≥100 mIU/mL. An anamnestic response was mounted in 92.5% of adolescents. Injection site pain (in 33.6% of participants) and fatigue (30.2%) were the most frequently reported solicited local and general symptoms, respectively. Six of the 55 unsolicited adverse events reported were considered vaccination-related. Two vaccination-unrelated serious adverse events were reported during the study. Long-term antibody persistence against hepatitis B was observed in 14-15 years old adolescents previously primed in infancy with DTPa-HBV-IPV/Hib. A challenge dose of monovalent HBV vaccine induced strong anamnestic response, with no safety concerns.

Persistence of hepatitis B immune memory until 9-10 years of age following hepatitis B vaccination at birth and DTaP-IPV-HB-PRP∼T vaccination at 2, 4 and 6 months

OBJECTIVE

To evaluate the long-term persistence of anti-hepatitis B surface (HBs) antibodies and the response to a HB challenge re-vaccination in children who had received a primary series of DTaP-IPV-HB-PRP∼T (Hexaxim™) or DTaP-IPV-HB/PRP∼T (Infanrix hexa™).

METHODS

Two cohorts of participants who had previously received HB vaccine at birth followed by either DTaP-IPV-HB-PRP∼T or DTaP-IPV-HB/PRP∼T co-administered with PCV7 at 2, 4, 6 months of age in a randomized, Phase III, observer-blind study in Thailand, were followed up for anti-HBs antibodies (geometric mean concentrations [GMCs] and seroprotection [SP] rate [% of participants with a titer ≥10 mIU/mL]) at 12-18 months of age and 9-10 years of age. A monovalent HB challenge re-vaccination was administered at 9-10 years of age and the anamnestic response was evaluated.

RESULTS

Anti-HBs GMCs and SP rates in the DTaP-IPV-HB-PRP∼T and DTaP-IPV-HB/PRP∼T groups were high and similar post-primary vaccination series (2477 mIU/mL and 99.5% and 2442 mIU/mL and 99.5%, respectively) and declined to a similar extent in each group at 12-18 months (154.5 mIU/mL and 90.8% and 162.3 mIU/mL and 96.5%, respectively). Antibody levels further declined at 9-10 years of age (13.3 mIU/mL and 49.3% and 8.0 mIU/mL and 42.9%) and a strong anamnestic response occurred in each group post-HB challenge re-vaccination (92.8% and 98.7%, respectively).

CONCLUSION

The kinetics of long-term anti-HBs antibody persistence were similar following a primary series of DTaP-IPV-HB-PRP∼T or DTaP-IPV-HB/PRP∼T. The response to a subsequent HB challenge re-vaccination was strong and similar in each group, demonstrating persisting immune memory.

Hepatitis B immune status in adolescents vaccinated during infancy: A retrospective cohort study from a pediatric practice in Germany

In Germany, vaccination of infants against hepatitis B is recommended since 1995. However, data on long-term immunity is sparse and the necessity of a booster dose remains uncertain. Aims of this study were to assess the long-term persistence of antibodies to the hepatitis B surface antigen (anti-HBs) after immunization during infancy and the effect of a subsequent hepatitis B booster vaccination during adolescence on anti-HBs levels. Patients from a private pediatric practice who had received a full vaccination course of hepatitis B as infants and who were quantitatively tested for anti-HBs during adolescence (pre-booster levels) were included. In those participants who received a hepatitis B booster, post-booster anti-HBs levels were measured. Univariate analyses were conducted to determine factors associated with pre- and post-booster anti-HBs levels, respectively. 106 participants (53% male) were included in the study. At an average of 13.7 y after primary vaccination, 14% of participants had an anti-HBs level of ≥100 IU/l, while 46% were at 10-99 IU/l and 40% had anti-HBs levels of <10 IU/l. In total, 34 received a booster vaccination. Of those, 97% (33/34) had post-booster anti-HBs levels ≥ 100 IU/l, which were independent from pre-booster levels. No other patient characteristics were associated with pre-booster or post-booster anti-HBs≥ 100 IU/l. Although almost half of study participants showed low anti-HBs levels at follow-up, robust responses to booster vaccination suggest that adolescents who received the full vaccination course during infancy are still protected against hepatitis B infection.

Lasting immune memory against hepatitis B in 12-13-year-old adolescents previously vaccinated with 4 doses of hexavalent DTPa-HBV-IPV/Hib vaccine in infancy

BACKGROUND

Vaccinating infants against hepatitis B virus (HBV) is the most effective way of preventing the disease. However, since HBV exposure can increase during adolescence, it is essential that antibody persistence is maintained. We evaluated the antibody persistence and immune memory against hepatitis B, in 12-13 y olds who had received complete primary + booster vaccination with diphtheria-tetanus-acellular pertussis-hepatitis B-inactivated poliovirus/Haemophilus influenza type b (DTPa-HBV-IPV/Hib) vaccine in infancy.

METHODS

Open phase-IV study conducted at 12 centers in Germany [NCT02052661]. Adolescents aged 12-13 y, vaccinated with 4 doses of DTPa-HBV-IPV/Hib (Infanrix hexa™, GSK Vaccines) in infancy, received a single challenge dose of monovalent pediatric hepatitis B vaccine (Engerix™-B Kinder; GSK Vaccines). Blood samples were taken before and 1-month post-challenge to measure anti-hepatitis B (anti-HBs) antibodies using a chemiluminescence immunoassay (seroprotection cut-off: ≥10 mIU/ml). Post-challenge adverse events (AEs) were monitored.

RESULTS

300 subjects were vaccinated; of 293 subjects in the ATP immunogenicity cohort, 60.5% had pre-challenge anti-HBs antibodies ≥10 mIU/ml, which rose to 97.6% post-challenge (≥100 mIU/ml in 94.1%). An anamnestic response was seen in 96.5% subjects. A 150-fold increase in antibody geometric mean concentrations was observed (22.4 to 3502.6 mIU/ml). Pain (44%) and fatigue (24.3%) were the most frequent solicited local and general AEs, respectively; 14.7% subjects reported unsolicited symptoms during the 31-day post-vaccination period. Two vaccine-unrelated serious AEs occurred.

CONCLUSION

Vaccination with DTPa-HBV-IPV/Hib in infancy induces sustained seroprotection and immune memory against HBV, as shown by the strong anamnestic response to the hepatitis B vaccine challenge in 12-13 year-old adolescents.

End Joining-Mediated Gene Expression in Mammalian Cells Using PCR-Amplified DNA Constructs that Contain Terminator in Front of Promoter

Mammalian gene expression constructs are generally prepared in a plasmid vector, in which a promoter and terminator are located upstream and downstream of a protein-coding sequence, respectively. In this study, we found that front terminator constructs-DNA constructs containing a terminator upstream of a promoter rather than downstream of a coding region-could sufficiently express proteins as a result of end joining of the introduced DNA fragment. By taking advantage of front terminator constructs, FLAG substitutions, and deletions were generated using mutagenesis primers to identify amino acids specifically recognized by commercial FLAG antibodies. A minimal epitope sequence for polyclonal FLAG antibody recognition was also identified. In addition, we analyzed the sequence of a C-terminal Ser-Lys-Leu peroxisome localization signal, and identified the key residues necessary for peroxisome targeting. Moreover, front terminator constructs of hepatitis B surface antigen were used for deletion analysis, leading to the identification of regions required for the particle formation. Collectively, these results indicate that front terminator constructs allow for easy manipulations of C-terminal protein-coding sequences, and suggest that direct gene expression with PCR-amplified DNA is useful for high-throughput protein analysis in mammalian cells.

Immunity to hepatitis B persists in adolescents 15-16 years of age vaccinated in infancy with three doses of hepatitis B vaccine

OBJECTIVE

Vaccination of infants against hepatitis B virus (HBV) using hepatitis B vaccine is effective in preventing the infection during early childhood and there is a growing evidence of long-term protection. So far, no need for a booster dose has been identified in healthy subjects; however further follow-up continues to determine the exact duration of protection. We evaluated antibody persistence and immune response to a hepatitis B vaccine challenge dose in children aged 15-16 years, previously vaccinated with 3-doses of the same vaccine in infancy (third dose received before 18 months of age).

METHODS

A single hepatitis B vaccine challenge dose containing 10μg hepatitis B surface (HBs) antigen was administered to adolescents aged 15-16 years. Blood samples were taken before and one month after the challenge dose to measure anti-HBs antibodies using a chemiluminescence immunoassay. Solicited local and general symptoms, as well as unsolicited and serious adverse events were recorded after the challenge dose.

RESULTS

303 subjects were enrolled, of whom 302 and 293 subjects formed the total vaccinated and according-to-protocol cohorts, respectively. Pre-challenge, 65.4% (95% CI: 59.6-70.9) subjects were seroprotected (anti-HBs antibody concentration ≥10mIU/mL). One month post-challenge, 97.9% (95% CI: 95.6-99.2) were seroprotected, while 90.8% (95% CI: 86.8-93.8) had anti-HBs antibody concentrations ≥100mIU/mL. The post-challenge geometric mean concentration (GMC; 4134.9 [95% CI: 3114.2-5490.1]) was 150-fold higher than the pre-challenge GMC. Overall, 96.9% (95% CI: 94.2-98.6) subjects mounted an anamnestic response. The safety and reactogenicity profile of the hepatitis B vaccine challenge dose was consistent with previous experience.

CONCLUSIONS

Immunity to hepatitis B persists in 15-16 year old adolescents following primary vaccination in infancy.

TRIAL REGISTRATION

http://www.clinicaltrials.govNCT01847430.

Markers of Protection in Children and Adolescents Six to Fourteen Years After Primary Hepatitis B Vaccination in Real Life: A Pilot Study

BACKGROUND

Not many data are available on long-term immunity against hepatitis B (HB) for children vaccinated under real-life conditions.

METHODS

Two hundred and thirty-two children and adolescents vaccinated 6-14 years earlier in pediatric practices were examined for conditions of vaccination and markers of protection as anti-HBs, anamnestic response to a booster dose and cell-mediated immunity.

RESULTS

Fifty-six percent of the participants were vaccinated according to the German vaccination recommendations (group 1). In 44.0% (group 2), these recommendations were not followed. Anti-HBs concentrations of ≥10 IU/L were found in 53.1% of group 1 and 45.1% of group 2 participants. A booster dose resulted in 91 of 99 participants in having an anamnestic response, in 3 (5.9%) of group 1 and 5 (10.4%) of group 2 anti-HBs remained below 10 IU/L. In group 1, postbooster anti-HBs concentration was inversely correlated with time since the last vaccination. Cellular immune responses were seen in only 5% of revaccinated individuals before the booster, increasing to 30% thereafter.

CONCLUSIONS

Under real-life conditions about half of vaccinees have lost protecting antibodies 6-14 years after vaccination in infancy, but in approximately 90% of them, immune memory was demonstrated. However, as memory may wane, revaccination at a time when boostability is still present might be considered.

The Serum Anti-HBs Level Among Children Who Received Routine Hepatitis B Vaccination During Infancy in Mianyang City, China: A Cross-Sectional Study

Hepatitis B virus (HBV) prevalence has declined remarkably in children due to nationwide universal vaccination program for HBV in China. However, the persistence of immune response against HBV infection and the optimal time point when a booster vaccination should be performed remain to be elucidated. To assess the persistence and level of antibody against hepatitis B surface antigen (anti-HBs) in a representative population of age 15 and younger who received routine hepatitis B vaccination in Mianyang City, China. A cross-sectional study was conducted in 2011. One thousand five hundred twenty-six children of age 15 and younger who received three doses of 5 μg hepatitis B vaccine series during infancy but did not receive a booster vaccination later were enrolled. Of the 1,526 children, the mean age was 8.2 ± 4.1 and 739 children were male. The median anti-HBs level was 23.0 mIU/mL, and the total percentage of anti-HBs levels ≥10 mIU/mL was 60.9%. With an increase of age, median anti-HBs level, percentage of anti-HBs levels ≥10 mIU/mL, and percentage of anti-HBs levels ≥100 mIU/mL declined remarkably in the early period and reached the lowest level at the age of 3 and then remained relatively stable. The median anti-HBs level, the percentage of anti-HBs levels ≥10 mIU/mL, and the percentage of anti-HBs levels ≥100 mIU/mL in 1- and 2-year-old children were much higher than that in children aged 3-15 (p < 0.05, respectively). Immunity against HBV infection gradually decreased in early ages of children of 15 and younger who received three doses of 5 μg hepatitis B vaccine series during infancy in China. Three dosages of 10 μg hepatitis B vaccine for infants and repeated vaccination or additional booster vaccination for some children at or before age 3 should be provided to get much more powerful immunity to HBV.