Non-Pharmaceutical Interventions Are Effective in Preventing SARS-CoV-2 Infection
Clinical Infectious Diseases: By Infectious Diseases Society of America
TAKE-HOME MESSAGE
This study addressed the predictors of SARS-CoV-2 infection among participants who reported social contact with an individual known or suspected of having SARS-CoV-2 infection. Among unvaccinated and partially vaccinated participants, factors such as interactions in indoor settings, ≥3 hours of interaction, and exposures with household members were associated with a high risk of infection.
Individuals who tested positive were less likely to report mask use during high-risk exposures compared with those who tested negative for SARS-CoV-2 infection. Furthermore, the benefits of mask use were greater among unvaccinated and partially vaccinated participants.
This study shows that non-pharmaceutical interventions, including mask use, reduce the risk of SARS-CoV-2 transmission.
The authors also demonstrated substantial vaccine effectiveness against SARS-CoV-2 with respect to high-risk interactions, suggesting that such exposures are not associated with an increased risk of vaccine failure.
Efforts to prevent transmission include social distancing and avoiding direct physical contact with nonhousehold members; interacting with nonhousehold member’s outdoors; and use of face coverings to filter virus-containing droplets and aerosols.
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BACKGROUND
Non-pharmaceutical interventions (NPIs) are recommended for COVID-19 prevention. However, the effectiveness of NPIs in preventing SARS-CoV-2 transmission remains poorly quantified.
METHODS
Authors conducted a test-negative design case-control study enrolling cases (testing positive for SARS-CoV-2) and controls (testing negative) with molecular SARS-CoV-2 diagnostic test results reported to California Department of Public Health between 24 February-12 November, 2021. Authors used conditional logistic regression to estimate adjusted odds ratios of case status among participants who reported contact with an individual known or suspected to have been infected with SARS-CoV-2 ("high-risk exposure") ≤14 days before testing.
RESULTS
751 of 1448 cases (52%) and 255 of 1443 controls (18%) reported high-risk exposures ≤14 days before testing. Adjusted odds of case status were 3.02-fold higher when high-risk exposures occurred with household members (vs. other contacts), 2.10-fold higher when exposures occurred indoors (vs. outdoors only), and 2.15-fold higher when exposures lasted ≥3 hours (vs. shorter durations) among unvaccinated and partially-vaccinated individuals; excess risk associated with such exposures was mitigated among fully-vaccinated individuals. Cases were less likely than controls to report mask usage during high-risk exposures. The adjusted odd of case status was lower for fully-vaccinated participants compared to unvaccinated participants.
Benefits of mask usage were greatest among unvaccinated and partially-vaccinated participants, and in interactions involving non-household contacts or interactions occurring without physical contact.
CONCLUSIONS
NPIs reduced the likelihood of SARS-CoV-2 infection following high-risk exposure. Vaccine effectiveness was substantial for partially and fully vaccinated persons.
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