Abstract
Age-specific genetic and antigenic variations of influenza viruses have not been documented in tropical and subtropical regions. We implemented a systematic surveillance program in two tertiary hospitals in Hong Kong Island, to collect 112 A(H1N1)pdm09 and 254 A(H3N2) positive specimens from 2013 to 2014. Of these, 56 and 72 were identified as genetic variants of the WHO recommended vaccine composition strains, respectively. A subset of these genetic variants was selected for hemagglutination-inhibition (HI) tests, but none appeared to be antigenic variants of the vaccine composition strains. We also found that genetic and antigenicity variations were similar across sex and age groups of ≤18 yrs, 18 to 65 yrs, and ≥65 yrs. Our findings suggest that none of the age groups led other age groups in genetic evolution of influenza virus A strains. Future studies from different regions and longer study periods are needed to further investigate the age and sex heterogeneity of influenza viruses.
Highlights
Influenza viruses undergo frequent antigenic drift, and cause winter epidemics in temperate regions and year-long circulation in tropical and subtropical regions
Characteristics of patients whose specimens were selected for sequencing and Hemagglutinin Inhibition (HI) tests were similar to those unselected patients, except that the percentage of children was slightly higher in the selected than in unselected group for A(H3N2) samples (Table 1)
Previous studies had reported that 1% and 0.8% of amino acids in HA1 domain changed per year for H1 and H3, respectively[11]
Summary
Influenza viruses undergo frequent antigenic drift, and cause winter epidemics in temperate regions and year-long circulation in tropical and subtropical regions. In Hong Kong, the influenza surveillance network managed by the Department of Health routinely selected potentially drifted specimens for genetic and antigenic characterization. Temporal variations of genetic and antigenicity characteristics have never been studied, largely due to the relatively small number of specimens which were subjectively selected based on antigenic drifts and disease severity, rather than from a representative sample of strains currently circulating in the whole population. We implemented a systematic surveillance program during 2013–2014, to randomly select a sample of positive specimens of children (aged below 18 years) and adults, from two tertiary hospitals in the Hong Kong Island each week. The systematically collected specimens were expected representative of concurrent circulating strains in the population[6] and could allow the investigation of temporal variations of genetic and antigenicity characteristics of concurrently circulating influenza viruses
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