Five years into the COVID-19 era, a persistent question has shadowed vaccine policy: does vaccination reduce not just an individual’s risk of serious illness, but their likelihood of spreading the virus to others? A new cohort study offers some of the clearest evidence yet in the current immunity landscape — and the answer, at least for recently vaccinated individuals, is yes.
Published May 15, 2026, in JAMA Network Open, the study found that individuals vaccinated against COVID-19 within the preceding six months were significantly less likely to transmit SARS-CoV-2 to people living in their household. The vaccine effectiveness against transmission in that window was estimated at 43%, with household contacts of recently vaccinated index cases facing roughly half the infection risk of contacts whose index case was unvaccinated.
A High-Exposure Setting Yields High-Resolution Data
The findings come from the Respiratory Infection: Gauge of Household Transmission (RIGHT) study, a prospective, case-ascertained household transmission investigation conducted across New York, Tennessee, and Washington from January 2024 through January 2025. Researchers enrolled the first confirmed SARS-CoV-2 case in a household — the “primary case participant” — along with their household contacts, then had all participants collect daily nasal swabs for ten days, tested via PCR regardless of symptoms. Vaccination histories were verified by study staff rather than relying solely on self-report. The analytic sample included 362 primary case participants and 763 household contacts.
The overall secondary infection risk in the study was strikingly high: 62.4% of household contacts tested positive for SARS-CoV-2 during the follow-up period, underscoring the efficiency of close-contact transmission and the ongoing burden of the virus even in a population with broad prior immunity. Roughly 43% of both primary cases and contacts showed evidence of prior SARS-CoV-2 infection via antibody testing, reflecting the high baseline population immunity that characterized the study period.
The Transmission Signal Is Real — But Time-Limited
The study’s central finding is that the transmission-blocking benefit of vaccination is real but wanes meaningfully with time. When primary case participants had been vaccinated within the previous six months, their household contacts faced an adjusted relative risk of infection of 0.57 compared with contacts of unvaccinated primary cases — a statistically significant reduction. For primary cases vaccinated seven to twelve months prior, and those vaccinated more than twelve months prior, the risk reduction trend continued but did not reach statistical significance, suggesting that protection against transmission, like protection against severe disease, diminishes over time.
Notably, the vaccination status of household contacts themselves did not significantly alter their risk of becoming infected — a finding the authors attribute in part to the study’s modest sample size limiting power to detect smaller effect sizes, and in part to the high-exposure dynamics inherent in household settings. The authors note that larger cohort studies have demonstrated statistically significant vaccine effectiveness against infection, and caution against interpreting this null finding as evidence that individual vaccination provides no protection.
Indirect Protection as a Public Health Security Asset
The study explicitly situates its results within high-exposure settings where index case vaccination status could meaningfully affect outbreak dynamics. At a population level, even a 43% reduction in the probability of transmission from an infected individual represents a substantial potential reduction in the effective reproduction number of the virus.
These findings reinforce the public health rationale for maintaining COVID-19 vaccination coverage not only among individuals at elevated risk of severe outcomes, but among those most likely to encounter and transmit the virus to vulnerable populations. In institutional settings such as nursing facilities, hospitals, and correctional facilities — environments that have historically amplified respiratory pathogen transmission — the indirect protective value of staff vaccination could be substantial. The data also add empirical weight to the concept of vaccine-mediated community protection, providing a mechanism by which immunization programs can reduce population-level viral burden even as direct protection against infection may be modest in a highly immune population.
The study has important limitations. Participants were recruited through outpatient health care settings, potentially skewing the sample toward those more health-engaged than the general population. The analysis did not account for multiple transmission chains within households or ongoing community exposure, and residual confounding from unmeasured behavioral factors cannot be excluded. The study also did not incorporate confirmed prior SARS-CoV-2 infection into its vaccine effectiveness estimates, which the authors acknowledge may bias results toward lower effectiveness.
Despite these caveats, the RIGHT study adds a timely and policy-relevant data point: in a population already carrying high baseline immunity, keeping COVID-19 vaccination current appears to meaningfully reduce contagiousness.
Sources and further reading:
Benist SC et al. Recent COVID-19 Vaccination and Risk of SARS-CoV-2 Transmission. JAMA Network Open. May 15, 2026.