Recent COVID-19 vaccination has been linked to a reduced risk of SARS-CoV-2 transmission in a prospective, case-ascertained household transmission study.
Household contacts of individuals vaccinated against COVID-19 within 6 months of disease onset had a 43-percent lower likelihood of contracting infection compared with household contacts of unvaccinated individuals (adjusted relative risk [aRR], 0.57, 95 percent confidence interval [CI], 0.35–0.93). The corresponding vaccine efficacy against transmission was 43 percent (95 percent confidence interval [CI], 7–65). [JAMA Netw Open 2026;9:e2612609]
However, the risk of transmission to household contacts did not significantly differ between individuals who were last vaccinated between 7 and 12 months or >12 months and unvaccinated individuals.
“The finding illustrates that recent COVID-19 vaccination may have indirect benefits by decreasing transmission to others,” according to the authors. Additionally, “COVID-19 vaccine protection against transmission may wane over time, similar to studies that considered other vaccine efficacy endpoints, including protection against severe illness.”
The takeaway is that “in high-exposure settings, such as households, one possible way to protect other household members is to get a COVID-19 vaccine. These results may be relevant to other high-exposure settings such as healthcare facilities and congregate work or living settings,” they said.
The study included 362 primary case participants (median age 35 years, 55 percent female, 50.8 percent White) and 763 household contacts (median age 29 years, 52.3 percent female, 41.7 percent White) across New York, Tennessee, and Washington in the US.
Primary case participants and household contacts had a similar distribution of COVID-19 vaccination status. The respective proportions of primary case participants and household contacts who had received a vaccine were 9.7 percent and 9 percent within 6 months of primary infection onset, 19.1 percent and 15.7 percent within 7–12 months of primary infection onset, and 45.9 percent and 45.7 percent within >12 months of primary infection onset.
SARS-CoV-2 infection was detected in 476 household contacts during follow-up, corresponding to a secondary infection risk of 62.4 percent (95 percent CI, 58.7–65.5). Symptoms were reported in all primary case participants and in 76.7 percent of household contacts who contracted SARS-CoV-2 infection.
The median time from symptom onset to enrolment was 4 days among primary case participants and 0 days among household contacts who had SARS-CoV-2 infection.
The authors acknowledged several study limitations, including the inability to account for multiple chains of transmission and ongoing SARS-CoV-2 infection risk from outside the household and the small sample size, among others.
Additionally, “household contact patterns between individuals are typically more frequent and physically closer, representing relatively high exposure compared with other non-household settings, so these findings may not apply to low-exposure settings,” they said.