Seroprevalence of influenza viruses in Shandong, Northern China during the COVID-19 pandemic

Abstract

Nonpharmaceutical interventions (NPIs) have been commonly deployed to prevent and control the spread of the coronavirus disease 2019 (COVID-19), resulting in a worldwide decline in influenza prevalence. However, the influenza risk in China warrants cautious assessment. We conducted a cross-sectional, seroepidemiological study in Shandong Province, Northern China in mid-2021. Hemagglutination inhibition was performed to test antibodies against four influenza vaccine strains. A combination of descriptive and meta-analyses was adopted to compare the seroprevalence of influenza antibodies before and during the COVID-19 pandemic. The overall seroprevalence values against A/H1N1pdm09, A/H3N2, B/Victoria, and B/Yamagata were 17.8% (95% CI 16.2%–19.5%), 23.5% (95% CI 21.7%–25.4%), 7.6% (95% CI 6.6%–8.7%), and 15.0 (95% CI 13.5%–16.5%), respectively, in the study period. The overall vaccination rate was extremely low (2.6%). Our results revealed that antibody titers in vaccinated participants were significantly higher than those in unvaccinated individuals ( P < 0.001). Notably, the meta-analysis showed that antibodies against A/H1N1pdm09 and A/H3N2 were significantly low in adults after the COVID-19 pandemic ( P < 0.01). Increasing vaccination rates and maintaining NPIs are recommended to prevent an elevated influenza risk in China. Electronic Supplementary Material Supplementary material is available in the online version of this article at 10.1007/s11684-022-0930-5 and is accessible for authorized users.

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“…Although annual influenza vaccination is recommended to the population older than 65 yo, with high vaccine coverage (≥ 60% since 2017/18), the lowest seroprevalence of protective antibodies against influenza A viruses was observed for the older age groups (45–64 and 65+ yo). These results add to existing evidence of immune senescence and pre‐existing immunity and a faster decrease of antibody titers with time and age, more pronounced in the elderly [20, 23]. For influenza B, which only predominated in circulation during one season, 2014/2015, and co‐circulated with A(H3N2) during 2015/2016 and 2017/2018, we observed an increasing trend in the seroprevalence of protective antibodies with age.…”

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