Epidemiology and control of influenza and other respiratory viruses in China

Abstract

Respiratory virus infections pose a significant public health challenge, particularly in vulnerable groups such as children and older adults. China faces challenges with low influenza vaccination coverage and limited data on the community burden of influenza virus infections. In some locations, healthcare settings can have a dense population of vulnerable patients, raising potential concerns on increased risk of infection with respiratory viruses. With the recent experience of the COVID-19 pandemic, there is an important need to review effective public health and social measures (PHSMs), including school-based management, to inform possible control strategies in China for preparedness against future epidemics and pandemics. My thesis includes several specific projects to address these overall aims.

In a longitudinal observational study of 1532 community-dwelling older adults aged 60-89 years in Jiangsu province from 2015 to 2017, I found that the age-adjusted cumulative incidence of influenza during winger-to-spring epidemics was 8-13%, based on serologic-confirmation of infection identified by hemagglutination inhibition (HAI) assay, and an additional 1.9-5.0% identified by enzyme-linked lection assay for neuraminidase inhibition antibodies. Lower pre-season HAI titers correlated with increased risk of symptomatic infections across virus strains. HAI titers of 40 against H1N1 were associated with 83.7% (95% CI: 71.3%, 90.7%) lower risk of serological infection, and anti-H3 associated with an 81.8% (95% CI: 74.4%, 87.0%) reduction in PCR-confirmed infection among ARIs patients compared to titers <10. Additionally, pre-season anti-N1 titers of 40 correlated with a 65.0% (95% CI: 56.7%, 71.7%) reduction in infection risk, and anti-N2 titers of 40 correlated with a 49.8% (95% CI: 36.9%, 60.1%) reduction, compared to titers <20.

In an air sampling study in 5-bed pediatric patient rooms in a tertiary hospital in Guangzhou using two-stage cyclone NIOSH samplers, influenza A virus was detected in 70% of 44 sampling occasions where at least one patient had a PCR-confirmed respiratory virus infection. Other viruses detected included influenza B (25%) and respiratory syncytial virus (27%). Respiratory viruses were detected in the air on some occasions when no patients in the room tested positive for the corresponding virus in a similar proportion. Viral loads across all detected respiratory viruses ranged from 103–105 copies/m3 air sampled.

I conducted a systematic review and meta-analysis on the effectiveness of school shutdowns and reopening for influenza and COVID-19, as well as school-based measures. I found that school closures decreased the effective reproduction number (Rt) by 7% to 86%, while reopening increased by 1% to 125% due to increased mobility. However, minimal in-school transmission was observed with multi-layer measures during the COVID-19 pandemic.

There is a need to increase annual influenza vaccination coverage in China to reduce overall influenza-related disease burden, as observed in other regions. Moreover, aerosol transmission of respiratory viruses in healthcare settings poses a potential exposure risk to other patients, as well as staff and visitors. Finally, in future pandemics it will be important to give careful consideration to school closures timing and duration, and consider implementing appropriate within-school measures to reduce transmission while avoiding the negative impacts of full closures.