Preparing for Future Pandemics: Vaccine Effectiveness Against SARS-CoV-2 Variant in a High-Risk Hospital Environment-A Case Study From Vietnam.

On 30 September 2021, Viet Duc University Hospital in Northern Vietnam, reported a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta outbreak, leading to an 18-day lockdown and repeated testing of all on-site individuals. At this time, SARS-CoV-2 was not yet circulating at scale among the general public and COVID-19 vaccination status varied among staff, patients, and caregivers. We estimated vaccine effectiveness (VE), attack rates (ARs), and adjusted risk ratios (aRRs) to identify factors associated with infection among infection-naïve patients, caregivers, and staff using multivariable regression analysis. Among 630 at-risk individuals, there were 131 (21%) polymerase chain reaction (PCR)-confirmed COVID-19 cases including three deaths. The overall VE was 78% (95% confidence interval [CI]: 59-88; P < .05). Hospital staff (aRR 0.20; 95% CI: 0.09-0.42) and people who were fully vaccinated (aRR 0.51; 95% CI: 0.28-0.95) had a significantly lower risk of SARS-CoV-2 infection (P < .05). Our analysis shows the importance of being fully vaccinated in reducing the risk of SARS-CoV-2 infection in hospital settings.