The coverage of rabies vaccinations has been reported at 70-80% of dogs in annual reports. However, there are still outbreaks of rabies among humans and dogs in Thailand, thus indicating the necessity of ensuring seroprevalence in vaccinated dogs and efficacy of human immunization. A cost effective easy competitive enzyme-linked immunosorbent assay (CEE-cELISA) was developed here for monitoring protective immunity against the rabies virus in human and dog serum samples using monoclonal antibody clone 1-46-12, which recognizes a conformational epitope of the rabies G protein. The ELISA plate is coated with the whole viral antigen from a commercial vaccine. The serotiter measured by the CEE-cELISA and by the gold standard assay (rapid fluorescent focus inhibition test), detecting the neutralizing antibody, showed a strong correlation, with an R value of 0.958 and 0.931 in humans and dogs, respectively. These correlations were detected in the serum samples from humans and dogs at antibody concentrations up to 100 and 10 IU/ml, respectively. This CEE-cELISA could be an alternative assay for evaluating mass rabies vaccination rapidly at a low cost as well as for detecting antirabies antibodies in the serum of not only humans but also other animal species.

Objective: Anti-HBs antibodies are elicited upon hepatitis B vaccination, and concentrations above 10 mIU/mL are considered protective. Our aim was to assess the relationship between IU/mL of anti-HBs and neutralization activity. Methods: Immunoglobulins G (IgGs) were purified from individuals who received a serum-derived vaccine (Group 1), a recombinant vaccine, Genevac-B or Engerix-B (Group 2), or who recovered from acute infection (Group 3). IgGs were tested for anti-HBs, anti-preS1, and anti-preS2 antibodies and for their neutralizing activity in an in vitro infection assay. Results: Anti-HBs IUs/mL value did not strictly correlate with neutralization activity. The Group 1 antibodies demonstrated a greater neutralizing activity than those of Group 2. Anti-preS1 antibodies were detected in Groups 1 and 3, and anti-preS2 in Group 1 and Group 2/Genhevac-B, but the contribution of anti-preS antibodies to neutralization could not be demonstrated. Virions bearing immune escape HBsAg variants were less susceptible to neutralization than wild-type virions. Conclusion. The level of anti-HBs antibodies in IUs is not sufficient to assess neutralizing activity. Consequently, (i) an in vitro neutralization assay should be included in the quality control procedures of antibody preparations intended for HB prophylaxis or immunotherapy, and (ii) a greater emphasis should be placed on ensuring that vaccine genotype/subtype matches with that of the circulating HBV.

Thailand has integrated Hepatitis B (HB) vaccine for newborns into the national Expanded Program on Immunization since 1992. The HB vaccination coverage was reported >96% in 2019 but the coverage among inhabitants of remote rural areas, particularly among hill-tribe children, remains unclear. This cross-sectional study aims to investigate the hepatitis B virus (HBV) seroprevalence among hill-tribe children living in 3 different areas in Omkoi District, Chiang Mai province, Thailand during September-November, 2018. Plasma samples were first tested for hepatitis B surface antigen (HBsAg). Sample negative for HBsAg were then tested for antibody to hepatitis B surface antigen (anti-HBs) levels and antibody to hepatitis B core antigen (anti-HBc). A total of 419 hill-tribe children were recruited, their median age was 11 years (interquartile range 9-12 years). Eighteen children (4.3%, 95%CI 2.6-6.7) were HBsAg positive. Among 401 remaining children, 269 had no HBV markers (67.1%, 95%CI 62.3-71.7), 91 (22.7%, 95%CI 18.7-27.1) were positive for anti-HBs only, 23 (5.7%, 95%CI 3.7-8.5) were positive for anti-HBc and anti-HBs, and 18 (4.5%, 95%CI 2.7-7.0) positive for anti-HBc only. The high prevalence of children susceptible to HBV infection and the high proportion of HBV infected children indicate that vaccination strategy needs to be improved in this rural area. Moreover, HBV serologic investigations are necessary in other rural areas to improve HB vaccination coverage. Keywords: Hepatitis B virus; Prevalence; Vaccination; Serological markers; Children; Thailand