Seroprevalence of Pandemic H1N1 Antibody among Health Care Workers in Hong Kong Following Receipt of Monovalent 2009 H1N1 Influenza Vaccine

Abstract

BackgroundHealthcare workers in many countries are recommended to receive influenza vaccine to protect themselves as well as patients. A monovalent H1N1 vaccine became available in Hong Kong in December 2009 and around 10% of local healthcare workers had received the vaccine by February 2010.MethodsWe conducted a cross-sectional study of the prevalence of antibody to pandemic (H1N1) 2009 among HCWs in Hong Kong in February–March 2010 following the first pandemic wave and the pH1N1 vaccination campaign. In this study we focus on the subset of healthcare workers who reported receipt of non-adjuvanted monovalent 2009 H1N1 vaccine (Panenza, Sanofi Pasteur). Sera collected from HCWs were tested for antibody against the pH1N1 virus by hemagglutination inhibition (HI) and viral neutralization (VN) assays.ResultsWe enrolled 703 HCWs. Among 104 HCWs who reported receipt of pH1N1 vaccine, 54% (95% confidence interval (CI): 44%–63%) had antibody titer ≥1∶40 by HI and 42% (95% CI: 33%–52%) had antibody titer ≥1∶40 by VN. The proportion of HCWs with antibody titer ≥1∶40 by HI and VN significantly decreased with age, and the proportion with antibody titer ≥1∶40 by VN was marginally significantly lower among HCWs who reported prior receipt of 2007–08 seasonal influenza vaccine (odds ratio: 0.43; 95% CI: 0.19–1.00). After adjustment for age, the effect of prior seasonal vaccine receipt was not statistically significant.ConclusionsOur findings suggest that monovalent H1N1 vaccine may have had suboptimal immunogenicity in HCWs in Hong Kong. Larger studies are required to confirm whether influenza vaccine maintains high efficacy and effectiveness in HCWs.

Immune response to 2009 H1N1 vaccine in HIV-infected adults in Northern Thailand

“…In conclusion, the unexpected low immune response to the single dose of non-adjuvanted 2009 H1N1 vaccine in our study together with similar results in the three other studies [23][24][25] suggest that the vaccine formulation Panenza ® bought by the Hong Kong and Thai government in late 2009 may be the cause of this suboptimal response. Alternatively, there might be problems with cold chain, vaccine management, or the sensitivity of laboratory method.…”

“…24 A similar study conducted in 104 Hong Kong healthcare workers aged 19-64 y receiving Panenza ® also showed seroprotection rate of 53.8% (95% CI 44.2% -63.2%). 25 One of the possible explanations for lower antibody response considered by the authors was imperfect effectiveness of Panenza ® .…”

Persistence and avidity maturation of antibodies to A(H1N1)pdm09 in healthcare workers following repeated annual vaccinations

“…Lower seroprotective titers have been reported for HCWs in Hong Kong (54%) and Japan (38%) after one dose of un-adjuvanted A(H1N1)pdm09 vaccine [37,38]. These inferior responses may be attributed to lack of adjuvant in the vaccines administered in these studies.…”

Two Years after Pandemic Influenza A/2009/H1N1: What Have We Learned?

“…Of 104 HCWs who received the A/2009/H1N1 vaccine in Hong Kong, only 42% had an antibody titer of Ն1:40 as detected by viral neutralization assay. The proportion of HCWs with an antibody titer of Ն1:40 significantly decreased with age (586). Additional studies are required to confirm whether the A/2009/H1N1 vaccine maintains high efficacy and effectiveness in HCWs and prevents the nosocomial transmission of the A/2009/ H1N1 virus.…”