Seroprevalence study suggests substantial H1N1 immunity in the USA; Factors influencing future H1N1 waves include social clustering, atmospheric conditions and virus competition

University of Pittsburgh researchers estimate that 21% of the U.S. population (63 million persons) have been infected with H1N1, and has developed immunity.

The research used 846 anonymous, leftover blood samples drawn on hospital and clinic patients from the Pittsburgh area in the mid-November and early December 2009 timeframe. Stored serum samples from 100 healthy, young adults from 2008 were used as a control group.

In addition to pandemic H1N1 (A/California/7/2009), the researchers examined seroprevalences against other virus strains to include: A/Brisbane/59/2007 (a seasonal H1N1 virus), A/Denver/1/1957 (a pandemic H2N2 virus) and A/South Carolina/1/1918 (a pandemic H1N1 virus).

Seroprevalences against pandemic 2009 H1N1 influenza varied by age group, with children age 10-19 years having the highest seroprevalence (45%), and persons age 70-79 years having the lowest (5%). The baseline seroprevalence among control samples from 18-24 year-olds was 6%. Overall seroprevalence against pandemic H1N1 across all age groups was approximately 21%.”

The study provided indications of prexisting immunity among seniors exposed to the 1957/1918 pandemic strains as suggested by the high seroprevalences found.

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Given these findings, and taking in account H1N1 vaccination efforts (at least 70 million Americans have been vaccinated), the authors conclude “that further sustained viral (pandemic H1N1) transmission is not likely.”

That said, no one is ready to declare an end to the pandemic. According to a panel of experts polled by the Washington Post, influenza “transmission waxes and wanes, and outbreaks of novel pandemic strains occur in particularly unpredictable waves that depend on such variables as human behavior, atmospheric conditions and even competition from other microbes.”

The report further adds “even if there isn’t a third wave, the new H1N1 may well spell the end of one or more of the families of flu virus that have been circulating for decades . That’s what’s happened in previous pandemics, at least.”

Adagio Teas

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