Delta Variant Spreads Rapidly through Vaccinated and Unvaccinated US Prison Population

A CDC examination of a Delta outbreak in a Texas prison showed unvaccinated persons have higher attack rates, hospitalizations, and deaths, but vaccinated persons can still contract and spread the virus.


US prisons have been disproportionately affected by the COVID-19 pandemic, largely due to the inability to practice social distancing. And the Centers for Disease Control and Prevention (CDC) reports that the Delta variant is spreading rapidly through incarcerated populations.

In July 2021, 74% (172 of 233) of inmates in a Texas federal penitentiary tested positive for the Delta variant.

Prisons have experienced unmitigated spread of COVID-19 since the beginning of the pandemic, but now the incarcerated population is largely vaccinated. At this Texas prison, 79% of inmates and 37% of staff members were fully vaccinated at the time of the Delta outbreak. While unvaccinated persons had far higher rates of hospitalization and mortality, the vaccinated population had similar numbers of positive COVID-19 tests.

The Federal Bureau of Prisons (BOP) was alerted to the outbreak on July 12, 2021, when 18 inmates in a living in interconnected housing units reported COVID-19 symptoms. Of these, 11 were vaccinated and all subsequently tested positive for COVID-19.

The CDC emphasized how critical it is for prison staff and visitors to stay home if they are symptomatic for or have been exposed to COVID-19, reporting, “SARS-CoV-2 can be introduced into correctional facility populations and back into the community through daily entry and exit…the identification of a single viral lineage among all sequenced specimens in this outbreak suggests a single introduction of the virus into the prison.”

Although vaccinated and unvaccinated persons had comparable numbers of COVID-19 infection during this outbreak, the CDC noted that fully vaccinated individuals who had been previously infected had the lowest attack rate.

Four persons were hospitalized, three of whom were unvaccinated, and one person died, also unvaccinated.

The CDC advised, “widespread vaccination among incarcerated persons and staff members in coordination with other prevention strategies, including early diagnostic testing for all persons with any COVID-19–like symptoms, screening testing, medical isolation, quarantine, masking, and physical distancing where possible, remain critical to limiting SARS-CoV-2 transmission and COVID-19–related illness and death in congregate settings, including correctional and detention facilities.”