Abstract
In pre- and post-immunisation sera from children (17-120 months-old) and adults (20-59 years-old) immunised with 2010/11 trivalent inactivated influenza vaccine, we assessed age-related patterns of sero-susceptibility and vaccine-induced cross-reactive antibodies to a representative swine H3N2 (swH3N2) and a related ancestral human H3N2 (A/Sydney/5/1997) influenza virus. Few children but a greater proportion of adults showed pre-immunisation haemagglutination inhibition titres ≥40 to either virus. Titres increased with age among children but decreased in adults. Fewer than 20% showed a four-fold rise in antibody titres to either virus following immunisation. Further investigation is warranted to guide ongoing risk assessment and response to emerging swine H3N2 viruses.
Highlights
The first documented human infection in North America with an influenza A(H3N2) virus of swine origin occurred in an Ontario farm worker in 2005 (A/Ontario/RV1273/2005)
Influenza A/Wuhan/359/1995 has not circulated in humans nor been a component of the trivalent inactivated influenza vaccine (TIV) since 1998, when it was replaced by influenza A/Sydney/5/1997(H3N2) [8,9,10]
Sera were tested for antibodies (i) to influenza A/ Wisconsin/15/2009(H3N2), considered antigenically equivalent to the influenza A/Perth/16/2009(H3N2)like component of the 2010/11 northern hemisphere TIV, (ii) to a swine H3N2 (swH3N2) virus (A/ferret/ QC/844/2011; F844) isolated from a ferret infected in February 2011 while temporarily housed with swine at the same Quebec animal research facility, and (iii) to influenza A/Sydney/5/97(H3N2) as a human influenza ancestor of swH3N2 (A/Sydney)
Summary
The first documented human infection in North America with an influenza A(H3N2) virus of swine origin (swH3N2) occurred in an Ontario farm worker in 2005 (A/Ontario/RV1273/2005). It involved a swH3N2 lineage that had entered swine from humans in the mid-1990s [1,2]. Sporadic human cases occurred thereafter in the United States (US) and Canada [3,4] During the latter half of 2011, 12 cases of human infection with a variant of swH3N2 (designated A(H3N2)v by the World Health Organization) [5] were identified in the US, primarily among children including some without recognised swine exposure [6]. Influenza A/Wuhan/359/1995 has not circulated in humans nor been a component of the trivalent inactivated influenza vaccine (TIV) since 1998, when it was replaced by influenza A/Sydney/5/1997(H3N2) [8,9,10]
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