🧵1/N How do vaccines and/or natural infection change infectiousness of #COVID19 during #Omicron? Our new article published in @NatureMedicine measures #COVID19 infectiousness, and finds reductions from both vaccine and natural infection. nature.com/articles/s4159… 
2/N We use detailed epidemiologic data from SARS-CoV-2 surveillance within the California prison system to study #COVID19 transmission. Our goal was to translate these findings into policy to improve health for this vulnerable incarcerated population that remains at high risk.
3/N We performed a close contact study of index cases with #COVID19 to measure their infectiousness, by comparing their vaccine and natural infection history. We followed their close contact (residents who shared a room) over time to estimate secondary attack rates. Design here:
4/N In our main analysis, we found that any #COVID19 vaccine reduced infectiousness by 22% (6–36%) and prior infection reduced infectiousness by 23% (3–39%). Hybrid immunity reduced infectiousness by 40% (20–55%).
5/N The raw numbers: Vaccinated residents with breakthrough infections were significantly less likely to transmit infection to others: 28% versus 36% for those who were unvaccinated.
6/N Key insight #1: The least infectious #COVID19 cases were those who had been recently vaccinated and/or had booster doses.
7/N Key insight #2: For persons previously infected, we found additional benefit of vaccination to further reduce infectiousness in subsequent #COVID19 infections.
8/N Policy take away #1: COVID-19 risk remains high in the incarcerated population and vaccines are not enough to stop transmission
9/N Policy take away #2: Based on our finding that people are least infectious within two months of vaccination, large timed vaccination campaigns may have a role to reduce transmission in surges. Future work is needed.
10/N Thank you to the team who made this work possible. Lead author Sophia Tan, upcoming super-🌟 in ID public health research. Dr. @realdavIDsears and Dr. @kwantada who made this collaboration possible. Appreciate support from California Correctional Health Care Services.
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