OBJECTIVES: To examine the relative effectiveness of vaccination and non-pharmaceutical interventions (NPIs) on COVID-19 infection, reproduction rate, and deaths in the US.

METHODS: Retrospective national-level US data were obtained from the Oxford COVID-19 Government Response Tracker (OxCGRT dataset). We performed time-trend analyses from December 2020 to December 2022 to observe how the values of policy variables and the number of COVID-19 new cases and deaths changed over time. The policy variables included (1) the number of people fully vaccinated per 100 of the total population (referred to as vaccination rate) and (2) the stringency index (a proxy for NPIs since it is a composite measure based on nine response indicators including school closures, workplace closures, stay-at-home requirements, and travel bans). We also performed multivariable linear regression to examine the associations between the policy variables and the COVID-19 reproduction rate.

RESULTS: Based on the time-trend analyses, the number of people vaccinated started to rise since March 2021, while the stringency index had steadily declined since early January 2021. A decrease in new COVID-19 cases and deaths was also observed during these three months (January to March 2021). However, despite a higher vaccination rate than in early 2021, new COVID-19 cases and deaths peaked in late 2021 and early 2022, suggesting that some NPIs might still be needed. The multivariable linear regression analysis showed that the reproduction rate of COVID-19 was negatively associated with the stringency index (coefficient = -0.010, 95% CI -0.013 to -0.005) and vaccination rate (coefficient = -0.005, 95% CI -0.009 to -0.001), after controlling for time covariates.

CONCLUSIONS: The study highlighted the importance of NPIs in reducing new COVID-19 cases and deaths even when vaccination was in progress. Further research accounting for other factors is needed to disentangle the effects of NPIs and other measures from vaccination campaigns.