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

Abstract

BackgroundInfluenza 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.ObjectivesTo 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.MethodsA cross‐sectional seroepidemiological study was conducted on 6911 serum samples collected before, during, and after the pandemic.ResultsCumulative 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.ConclusionsOur 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).

Relationships between A(H1N1)pdm09 influenza infection and infections with other respiratory viruses

“…In 2009, the A(H1N1)pdm09 virus was new to the population, and therefore ,individuals of all age groups were infected; however, in agreement with other reports, the elderly population was less infected with the virus . In contrast, by 2010–2012, around 50% of the population had already developed immunity against A(H1N1)pdm09 . During this round of infection, 44% of the patients were children under the age of 10, 58% of which were infants under the age of 1 year, born after the 2009 A(H1N1)pdm09 infection had already declined.…”

Ineffectiveness of the 2014-2015 H3N2 influenza vaccine

“…To determine the ability of antibodies elicited by the 2014-2015 influenza vaccine, to neutralize the new circulating influenza A(H3N2) virus, we obtained sera from 21 individuals, that had received the 2014-2015 influenza vaccine and tested them against the influenza A(H3N2) A/Texas/50/2012 and the influenza A(H3N2) A/Israel/P-151/2014 virus using a microneutralization assay [ 9 ]. Positive controls were for the A/Texas/50/2012 antibodies that were obtained from the WHO and gave a titer of 2560.…”

“…The presence of viral protein was detected by ELISA as previously described [ 9 , 14 ]. Specifically, the presence of viral protein was detected by ELISA with a monoclonal antibody to the influenza A NP (clone A-1 and A-3, Millipore).…”

Model-based reconstruction of an epidemic using multiple datasets: understanding influenza A/H1N1 pandemic dynamics in Israel

“…The virological data used here are the results of RT-PCR tests conducted on throat and nasal swabs collected from suspected influenza cases visiting clinics belonging to the Israeli Ministry of Health's sentinel network. The serology data contain the results of haemagglutination inhibition (HI) assays performed on serums collected from individuals prior to and during the 2009 pandemic [21]. The clinical surveillance data consist of diagnoses made by physicians belonging to the Macabbi health maintenance organization (HMO), which has a nationwide coverage of approximately 25% of the Israeli population.…”