Transmission and control of influenza of COVID-19

Abstract

Influenza viruses cause a substantial burden of morbidity and mortality around the globe. Influenza vaccination is the primary preventive measure against influenza especially for high-risk populations including older adults. Hong Kong, located in a subtropical region, can experience both winter and summer influenza seasons. Since vaccine effectiveness can wane over time, twice-annual vaccination might be an alternative vaccination strategy to enhance the protection against influenza during summer influenza seasons. To examine the effect of twice-annual vaccination in older adults, the immune responses to twice-annual vaccination and once-annual vaccination were evaluated using data from a 5-year randomized controlled trial. Results showed that twice-annual vaccination was able to provide an extra boost to immunity during summer influenza seasons. Further studies could investigate the cost-efficiency of twice-annual vaccination strategy.

Influenza vaccination has been suggested to have a non-specific effect on cardiovascular outcomes but results were inconclusive. It is crucial to have a comprehensive understanding of the vaccine efficacy or effectiveness on each of the major cardiovascular outcomes. I conducted a literature review and meta-analysis to examine the effect of influenza vaccination on cardiovascular outcomes. The findings suggested that influenza vaccination were associated with reductions in some of the cardiovascular outcomes in observational studies and randomized controlled trials. More randomized controlled trials with higher power and mechanistic studies would be needed to further explore the effect on some cardiovascular outcomes and mechanisms driving the effect on reduction.

The COVID-19 pandemic has had a considerable social and health impact in Hong Kong. Understanding the role of superspreading in COVID-19 transmission is crucial in estimating the transmissibility and dispersion over time. I estimated the effective reproduction number, time-varying dispersion parameter and proportion of cases responsible for 80% of transmission using negative binomial distribution and compared the effective reproduction number with the one estimated by the standard Poisson approach using incidence data during COVID-19 epidemics in Hong Kong. Estimated time-varying dispersion parameter was consistent with the occurrence of superspreading events in both waves. Around 20% of cases were responsible for 80% of transmissions during the early phase of an epidemic in 2020/21. Future studies could be done to explore using different types of data including genetic sequence data to identify transmission chains.

Finally, continued assessment of effectiveness of public health social measures is important for policy makers to evaluate and improve the interventions for future epidemics. During community epidemics of COVID-19 in 2020 and 2021, dine-in hours of restaurants were restricted after 6 pm as an attempt to contain the spread of COVID-19. I found no effect of this reduction in dine-in hours on reduced transmissibility estimated by both approaches. Further studies could explore the effectiveness of alternative measures to reduce transmission in restaurants.