The secondary attack rate (SAR), defined as the probability that an infection occurs among susceptible people within a specific group (ie, household or close contacts), can provide an indication of how social interactions relate to transmission risk. (The Lancet)

The secondary attack rate for SARS-CoV-2 — the virus causing coronavirus disease (COVID-19) — is under 1% among close contacts of U.S. patients, according to findings in MMWR. (NEJM Journal Watch)

The estimated secondary attack rate was 685 per 100 000 among household contacts, 404 per 100 000 among day-care nursery contacts and 77 per 100 000 among pre-elementary school contacts. (Science Direct)