The dynamics of infection and the persistence of immunity to A(H1N1)pdm09 virus in Israel

Merav Weil*, Tamar Shohat, Michal Bromberg, Ravit Bassal, Rita Dichtiar, Michal Mandelboim, Danit Sofer, Dani Cohen, Ella Mendelson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Background: Influenza virus A(H1N1)pdm09 first appeared in Israel in late April 2009, disappeared in mid-March 2010, and reappeared in late October 2010. Symptoms were mostly mild without need for medical care. Objectives: To provide targets for future pandemic preparedness and response by evaluating the dynamics and cumulative incidence of A(H1N1)pdm09 infection, the virus-specific seroprevalence (HI antibody titer >1:40) at the height of the pandemic, during its decline and thereafter. Methods: A cross-sectional seroepidemiological study was conducted on 6911 serum samples collected before, during, and after the pandemic. Results: Cumulative incidence of infection derived from the differences between post- and pre-pandemic seroprevalence was 54·1%, 32·9%, 22·9%, 14·8%, and 6·3% in age-groups 0-9, 10-19, 20-49, 50-79, and ≥80 years, respectively, and 28·5% for all age-groups combined. Vaccination could have contributed at the most 4·6% to the post-pandemic population seroprevalence. High pre-pandemic immune response (47·4%) found in a cohort aged 15-18 year was strongly associated with birth years 1990-1993. Morbidity began to decline in mid-November 2009 at 32·8% population seroprevalence (45% in ages 0-19 year) and stopped in March 2010 at 43·4% population seroprevalence in February 2010 (70% in ages 0-19 year). Between February and September 2010, seroprevalence declined by 12·2% allowing virus recirculation from October 2010. Conclusions: Our study provides targets for controlling future influenza pandemics in Israel. Vaccination should focus on the younger age-groups (0-19 year) which played a key role in transmission of the A(H1N1)pdm09 due to lack of background immunity (ages 0-9 year) and high exposure rates (ages 10-19 year).

Original languageEnglish
Pages (from-to)838-846
Number of pages9
JournalInfluenza and other Respiratory Viruses
Volume7
Issue number5
DOIs
StatePublished - Sep 2013

Keywords

  • A(H1N1)pdm09
  • Immunity
  • Incidence
  • Pandemic
  • Seroprevalence

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