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Sophie Valkenburg [HKU-PRP], Ben Cowling [School of Public Health] and co-workers to publish

on Influenza vaccination in older adults in Hong Kong

The paper “Immune Responses to Twice-Annual Influenza Vaccination in Older Adults in Hong Kong“ has been published in Clinical Infectious Diseases by the Oxford University Press for the Infectious Diseases Society of America.

Many health authorities recommend influenza vaccination of older adults to reduce diseases burden. The team hypothesized that in tropical and subtropical areas with more prolonged influenza seasons, twice-annual influenza vaccination might provide older adults with improved immunity against influenza.

In 2014-2015, Hong Kong experienced a substantial A(H3N2) winter epidemic with a mismatched vaccine. Local authorities procured and administered to older adults the 2015 southern hemisphere influenza vaccine, which included an updated and matching A/Switzerland/9715293/2013(H3N2) strain. They compared immune parameters in pre- and post vaccination sera from older adults ⩾75 of age who received 1 vs 2 influenza vaccines per year.

The team enrolled 978 older adults with 470 vaccinations for summer 2015 and 827 vaccinations for winter 2015-2016. Recipients of southern hemisphere vaccination had higher geometric mean titers (GMTs) by the hemagglutination inhibition assay against all 3 vaccine strains. When receiving influenza vaccination for the subsequent winter, the southern hemisphere vaccine recipients had higher revaccination GMTs but lower post vaccination GMT’s, compared to those who had not received the southern hemisphere vaccine. Furthermore, cellular immunity was impacted by biannual vaccination, with reduced influenza-specific CD4 T-cell responses in the second season of vaccination.

They observed some reductions in immune responses in the twice-annual vaccination group compared with the once-annual vaccination group, in the context of unchanging vaccine strains, while protection was likely to have been improved during the summer and autumn for the twice-annual vaccination group due to the continued circulation of the A/Switzerland/9715293/2013(H3N2) virus.The study is being continued with support from the CDC to test over a longer time period.

The publication is available on the Oxford Academic website.


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