H1N1v at a seroepidemiological glance: is the nightmare over?

Abstract

When the second wave of pandemic influenza A H1N1v 2009 (H1N1v) emerged in the winter of 2010/2011, public health authorities were afraid of dangerous implications and severe clinical courses again. As further H1N1v waves might appear, achievement of sufficient herd immunity is a matter of urgency. The objective of this study was to determine the seroprevalence of antibodies against H1N1v by hemagglutination-inhibition test (HI) after the second wave. We compared our recent findings with our data obtained after the first pandemic in 2009/2010. Between March and May 2011 we collected serum samples from 600 persons aged 1 to 84 years admitted to University Hospital Frankfurt/Main and analysed the titres of anti-H1N1v by HI. The overall seroprevalence of anti-H1N1v has risen from 36.9% (95% confidence interval (95%CI), 33-41) in unvaccinated persons after the first wave to 57.3% (95%CI, 53.1-61.2) in vaccinated and unvaccinated. The highest rate of seropositivity was detected in the age group of 10-19 years (66%; 95%CI, 55.8-75.2), whereas the lowest was found in the age group 40-59 years (51%; 95%CI, 40.8-61.1). Although seroprevalence has significantly increased, sufficient herd immunity is still not achieved. Therefore, general vaccination programs have to be propagated continuously by public health authorities.

Pandemic Influenza A(H1N1)pdm09 Seroprevalence in Sweden before and after the Pandemic and the Vaccination Campaign in 2009

“…The discrepancy was most striking in people above 36 years, perhaps reflecting an aging immune system with a broad repertoire but decreased ability to mount responses of high magnitude. Increasing A(H1N1)pdm09 seroprevalence between 2010 and 2011 has also been reported from other countries [24]–[26]. Despite the over-all increase in seroprevalence between May 2010 and May 2011 there was an over-all decrease in median HI titer among responders.…”

Pandemic Influenza A/H1N1pdm in Italy: Age, Risk and Population Susceptibility

“…In European countries serial seroepidemiological studies were conducted in United Kingdom [6], [12], where a considerable increase in HI antibody titers in children living in metropolitan areas from 1.8% to 23% (0 to 4 years) and from 3.7% to 46% (5 to 14 years), was shown, and similar results were found in Scotland [44]. In Germany [8]–[10], [15], [16], in Greece Maltezou, 2011 2205/id}, France [17], Sweden [18] and Norway [11] results showed increasing antibody titers mostly in younger age groups, but also in the elderly [11]. With regard to overseas countries, similar serial seroprevalence studies were conducted in the US where an overall increase of seroprevalence from 6% to 21% was found with the highest prevalence observed among children aged 0 to 19 years, followed by over- 80-year-olds, while no increase in seroprevalence was observed among the 70- to 79-year-olds.…”

Vaccination against infectious diseases: What is promising?

“…This has been recently shown again by the worldwide epidemic of swine-origin influenza virus A/H1N1pdm [4,33]. It has now replaced the conventional H1N1 strain, which had re-emerged 1978, as many seroprevalence studies show [34][35][36][37]. Based on recent research on avian flu [38], modern vaccines against the new human H1N1 strain could be rapidly created and applied [39][40][41].…”