Changing responses to public health measures during the COVID-19 pandemic

Abstract

On December 31, 2019, several instances of atypical pneumonia were reported to the World Health Organization in Wuhan, China, triggering the eventual global COVID-19 pandemic. Various public health measures, including non-pharmaceutical interventions (NPIs) and vaccines, were implemented worldwide to slow the spread. However, NPIs fatigue and vaccine hesitancy are expected as consequences of waning motivation to follow recommended public health measures.

I used data from 104 cross-sectional surveys from January 2020 to September 2022, representing the population in Hong Kong, to estimate that the participants had high levels of compliance with personal protective behaviors, while compliance with physical distancing measures and vaccination intention varied. Under comparable NPIs, the effective reproduction rates during post-intervention periods were higher in the November–December 2020 wave than in the June–July 2020 wave. Using a compartmental transmission model fitted to the local cases from 1 November 2020 to 10 January 2021, I found that the predicted pandemic size decreased when compliance rates increased.

An anonymous snowball sampling questionnaire survey in Mainland China was conducted to examine the facilitators and barriers to COVID-19 vaccine intention by the Health Belief Model at the early stage of vaccine implementation. I found that the perceived disease severity, the safety and accessibility of the vaccine, medical-related workers' recommendations, and vaccination history were significantly associated with vaccination intention. Both direct and indirect effects of “waiting to see what other people do” on vaccine intention were observed. However, it is not representative enough according to the sampling method.

I then used data from the surveys in Hong Kong to find that compliance with NPIs was usually associated with a higher vaccine intention in most rounds of surveys after mass implementation of the COVID-19 vaccines. Those who complied with all or most social distancing measures in the past 7 days were more likely to report uptake next dose of vaccine.

Additional doses of COVID-19 vaccines are now being used in high-risk groups to reduce disease burden, and one important area of research is the optimal timing of these doses, relating to the speed of waning if we assume the same strains. Without detailed data on waning of COVID-19 antibodies after vaccination, I conducted a systematic review and meta-analysis of vaccine-induced antibodies immunity and vaccine efficacy (VE) waning over a prolonged period (>10 years) of pertussis-, diphtheria-, tetanus- and polio-related vaccines. I discovered a significant reduction in pertussis and diphtheria immunity or VE, but residual tetanus and polio antibodies remain.

In summary, my thesis finds that responses on compliance with NPIs and vaccination intention change over time, and managing fatigue with NPIs and vaccine hesitancy are hence important components of pandemic mitigation. Cross-sectional surveys provide valuable data on temporal changes throughout all pandemic phases, including before and after the launch of COVID-19 vaccination program and the Omicron transmission in Hong Kong. Understanding the factors impacting vaccine intention will help in achieving high vaccination uptake. Examining the waning immunity is essential for choosing the optimal booster intervals to maintain protection among target groups.