Recent COVID-19 Vaccination Associated With Nearly Half the Risk of Household Transmission

SARS-CoV-2 continues to cause significant morbidity and mortality in the United States, with the 2024 to 2025 season contributing an estimated 320,000 to 480,000 hospitalizations and up to 56,000 deaths. While the benefit of COVID-19 vaccines in preventing severe illness, hospitalization, and death is well established, their role in reducing onward viral transmission, particularly within close-contact settings, has been less thoroughly studied, especially in the era of widespread population immunity from prior infection and vaccination.^1,2

A new cohort study published in JAMA Network Open addresses this gap directly, offering some of the most current household-transmission data available. The findings carry meaningful implications for pharmacists who counsel patients on the value of staying up to date with COVID-19 vaccination.³

Study Design

Conducted as part of the CDC's Respiratory Infection: Gauge of Household Transmission (RIGHT) study, the prospective, case-ascertained investigation enrolled households across New York, Tennessee, and Washington from January 2024 through January 2025. A total of 362 primary case participants (defined as the first household member with laboratory-confirmed SARS-CoV-2 infection) were enrolled alongside 763 household contacts.³

All participants collected daily nasal swabs for 10 days regardless of symptom status, which were tested via reverse transcription-polymerase chain reaction (RT-PCR). COVID-19 vaccination status was verified by study staff and categorized by time from most recent dose to primary case participant symptom onset: 6 months or fewer, 7 to 12 months, more than 12 months, and unvaccinated.³

Key Findings

Among the 763 household contacts, 476 (62.4%) tested positive for SARS-CoV-2 during follow-up, illustrating how efficiently the virus spreads in shared living environments. However, a significant protective signal emerged based on the vaccination status of the infected index case.³

Household contacts of primary case participants who had been vaccinated within the prior 6 months had a substantially lower risk of infection compared with contacts of unvaccinated primary cases (adjusted relative risk [ARR], 0.57; 95% CI, 0.35-0.93), translating to a vaccine effectiveness against transmission (VEt) of 43% (95% CI, 7%-65%). In other words, recently vaccinated individuals who contracted COVID-19 were roughly half as likely to pass the virus on to those living with them.³

This protective effect was not statistically significant when vaccination had occurred either 7 to 12 months or over 12 months prior to onset, which is a pattern consistent with prior observations that COVID-19 vaccine protection wanes over time across multiple outcome measures. Notably, the vaccination status of household contacts themselves did not significantly reduce their own likelihood of becoming infected, though the authors acknowledged that limited statistical power may have obscured a real effect, pointing to larger cohort studies that have demonstrated meaningful vaccine effectiveness against infection.²

Context and Implications for Practice

The study was conducted at a time when population immunity from prior infection was widespread. Despite this high baseline immunity, recent vaccination still conferred a meaningful reduction in transmissibility, suggesting an incremental benefit beyond infection-induced immunity alone.³

These findings are particularly timely given the current policy landscape. In September 2025, the CDC's Advisory Committee on Immunization Practices voted unanimously to shift COVID-19 vaccination to a shared clinical decision-making framework for all individuals aged 6 months and older, with an emphasis that the risk-benefit balance is most favorable for those at increased risk of severe disease, particularly adults aged 65 years and older. In this environment, pharmacists are uniquely positioned to guide patients through individualized vaccination decisions.¹

Waning Immunity: A Reason to Stay Current

The temporal pattern in the RIGHT study—with statistically significant transmission reduction only among those vaccinated within 6 months—emphasizes the importance of timely, updated vaccination. This aligns with data from the 2024 to 2025 season showing that while the updated KP.2-targeting vaccines offered strong protection against death (approximately 65%), effectiveness against infection and hospitalization was more modest and declined meaningfully over time. Pharmacists advising patients should emphasize that protection against transmitting COVID-19 to others, like protection against severe disease, is time-limited and renewed by updated seasonal doses.²

Conclusion

The RIGHT study offers compelling real-world evidence that recent COVID-19 vaccination carries indirect benefits beyond individual protection—reducing the likelihood of onward transmission to household contacts by nearly half. As COVID-19 vaccination transitions toward a shared decision-making model, pharmacists should incorporate this evidence when counseling patients who live with high-risk individuals. Staying up to date is not only self-protective; it may help shield the people closest to them.

REFERENCES

1. ACIP Recommends COVID-19 Immunization Based on Individual Decision-making. U.S. Department of Health and Human Services. September 19, 2025. Accessed May 27, 2026. https://www.hhs.gov/press-room/acip-recommends-covid19-vaccination-individual-decision-making.html

2. Ma KC, Webber A, Lauring AS, Bendall E, et al. Effectiveness of 2024-2025 COVID-19 Vaccination Against COVID-19 Hospitalization and Severe In-Hospital Outcomes - IVY Network, 26 Hospitals, September 1, 2024-April 30, 2025. medRxiv [Preprint]. 2025 Sep 3:2025.08.29.25334612. doi:10.1101/2025.08.29.25334612.

3. Benist SC, Smith-Jeffcoat SE, Talbot HK, et al. Recent COVID-19 Vaccination and Risk of SARS-CoV-2 Transmission. JAMA Netw Open. 2026;9(5):e2612609. doi:10.1001/jamanetworkopen.2026.12609