Abstract
BackgroundThe outbreak of the 2009 H1N1 influenza pandemic (H1N1pdm) affected thousands of people in Mexico and the United States, and spread rapidly throughout the world from April 2009 to July 2010. To explore the age-specific prevalence of seroprotection against H1N1pdm infection, we estimated pre-existing humoral and cellular immunities of residents in Northern China against H1N1pdm and seasonal H1N1 virus in an age-dependent manner.MethodsAnonymous serum samples were collected from 1425 to 1434 adult healthy individuals before and after the pandemic outbreak, and then grouped by birth year 1913–1990. The antibody titers of H1N1pdm and seasonal H1N1 were determined using microneutralization (MN) assays, and the proportion of seropositive was estimated based on the year of birth. Separately, another 63 blood samples were collected in 2006 and prepared for analysis of virus specific memory B and IFN-γ+ T cells using the ELISpot assays.ResultsThe prevalence of pre-existing H1N1pdm-specific sero-antibodies in the elderly population (>60 years old) was 7.8%. The younger group, aged 19 to 60 years, exhibited a significant increase in seropositivity for H1N1pdm after the pandemic (4.9% before pandemic and 18.9% after pandemic, p < 0.05). The prevalence of H1N1pdm specific MBCs before the pandemic in the elderly (>60 years) and younger populations (<60 years) was 38% (8/21) and 48% (20/42), respectively (p = 0.6). The IFN-γ+ T cell responses to the pandemic and seasonal viruses were significantly lower in the elder group than those in the younger group (<60 years) (p < 0.05).ConclusionsPre-existing serum antibodies and memory B cells against H1N1pdm were low in all age group, whereas diminished memory T cell responses to this virus were observed in the elderly population both before and after the pandemic.
Highlights
The outbreak of the 2009 H1N1 influenza pandemic (H1N1pdm) affected thousands of people in Mexico and the United States, and spread rapidly throughout the world from April 2009 to July 2010
Serum samples from 1425 individuals prepandemic were collected from June, 2008 to April, 2009, and 1434 serum samples post-pandemic were collected from January to July 2010
Elder people over 60 years of age had a higher seroprevalence (7.8%) than younger people under 60 years (4.9%, p = 0.035) before the pandemic, there were no significant difference of geometric mean titers (GMT) between the elder people (12, 95% CI: 12–13)
Summary
The outbreak of the 2009 H1N1 influenza pandemic (H1N1pdm) affected thousands of people in Mexico and the United States, and spread rapidly throughout the world from April 2009 to July 2010. In April 2009, an outbreak of H1N1 influenza initially hit Mexico and rapidly spread to other countries and regions of the world. In January 1976, a novel virus subtype, A/ New Jersey/76 H1N1, was identified in an outbreak of respiratory disease occurred among soldiers returning to an Army base in Fort Dix, New Jersey. This virus subtype did not escape from the base [5]. The 2009 pandemic H1N1 virus (H1N1pdm) was antigenically similar to pre-1950 influenza strains [7] and A/New Jersey/76 H1N1 strain [8]
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