RESUMO
In response to the COVID-19 pandemic, widespread non-pharmaceutical interventions (NPIs), including physical distancing, mask wearing, and enhanced hygiene, have been implemented. As of March 2021, three effective vaccines have been approved for emergency use in the United States, with several other vaccines in the pipeline. We use a transmission model to study when and how NPIs could be relaxed in the United States with relative safety as vaccination becomes more widespread. We compare different relaxation scenarios where NPIs begin to relax 0-9 months after vaccination begins for both a one dose and two dose strategy, with historical levels of social interactions being reached within 1 month to 1 year. In our model, vaccination can allow widespread relaxation of NPIs to begin safely within 2 to 9 months, greatly reducing deaths and peak health system burden compared to relaxing NPIs without vaccination. Vaccinated individuals can safely begin to relax NPIs sooner than unvaccinated individuals. The extent of delay needed to safely reopen depends primarily on the rate of vaccine rollout, with the degree of protection against asymptomatic infection playing a secondary role. If a vaccination rate of 3 million doses/day can be achieved, similar to the typical rollout speed of seasonal influenza vaccination, NPIs could begin to be safely relaxed in 2-3 months. With a vaccination rate of 1 million doses/day, a 6-9-month delay is needed. A one dose strategy is preferred if relative efficacy is similar to a two-dose series, but the relative benefit of this strategy is minimal when vaccine rollout is fast. Due to the urgent need to pursue strategies that enable safe relaxation of NPIs, we recommend a two-dose strategy with an initial delay of at least 3 months in relaxing restrictions further, and that the speed of vaccine rollout be given immediate priority.
RESUMO
ImportanceThe impact of non-pharmaceutical interventions (NPIs) in response to the SARS-CoV-2 pandemic on incidence of other infectious diseases is still being assessed. ObjectiveTo determine if the observed change in reported norovirus outbreaks in the United States was best explained by underreporting, seasonal trends, or reduced exposure due to NPIs. We also aimed to assess if the change in reported norovirus outbreaks varied by setting. DesignAn ecologic, interrupted time series analysis of norovirus outbreaks from nine states reported to the National Outbreak Reporting System (NORS) from July 2012-July 2020. SettingSurveillance data from Massachusetts, Michigan, Minnesota, Ohio, Oregon, South Carolina, Tennessee, Virginia, and Wisconsin were included in the analysis. Participants9,226 reports of acute gastroenteritis outbreaks with norovirus as an epidemiologically suspected or laboratory-confirmed etiology were included in the analysis, resulting in more than 8 years of follow up. Outbreak reports from states that participated in NoroSTAT for at least 4 years were included in the analysis (range: 4-8 years). ExposureThe main exposure of interest was time period: before (July 2012-February 2020) or after (April 2020-July 2020) the start of NPIs in the United States Main outcomeThe main outcome of interest was monthly rate of reported norovirus outbreaks. As a secondary outcome, we also examined the average outbreak size. ResultsWe found that the decline in norovirus outbreak reports was significant for all 9 states considered (pooled incidence rate ratio (IRR) comparing April 2020-July 2020 vs. all pre-COVID months for each state= 0.14, 95% CI: 0.098, 0.21; P=<0.0001), even after accounting for typical seasonal decline in incidence during the summer months. These patterns were similar across a variety of settings, including nursing homes, child daycares, healthcare settings, and schools. The average outbreak size was also reduced by 61% (95% CI: 56%, 42.7%; P=<0.0001), suggesting that the decline does not reflect a tendency to report only more severe outbreaks due to strained surveillance systems, but instead reflects a decline in incidence. Conclusions and relevanceWhile NPIs implemented during the spring and summer of 2020 were intended to reduce transmission of SARS-CoV-2, these changes also appear to have impacted the incidence of norovirus, a non-respiratory pathogen. These results suggest that NPIs may provide benefit for preventing transmission of other human pathogens, reducing strain to health systems during the continued SARS-CoV-2 pandemic. DisclaimerThe findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the US Centers for Disease Control and Prevention (CDC).
