COVID Vaccines No Match for a Delta Prison Outbreak

Unvaccinated inmates at a Texas prison experienced more severe COVID outcomes, but vaccinated inmates were certainly not immune during an outbreak of the Delta variant, researchers found.

Thirty-nine of 42 unvaccinated inmates tested positive (93%) versus 129 of 185 vaccinated inmates (70%; P=0.002), reported Liesl Hagan, MPH, of the CDC and colleagues.

Time since vaccination also appeared to play a role, with a significantly higher proportion of inmates vaccinated at least 4 months prior to the outbreak testing positive (80%) compared to inmates vaccinated 2 weeks to 2 months prior to the outbreak (61%; P<0.001), they wrote in an early edition of the Morbidity and Mortality Weekly Report.

Three of four of those hospitalized were unvaccinated, and one unvaccinated person required ICU care, including mechanical ventilation, and ultimately died, they noted.

Congregate settings were among the groups initially prioritized for COVID-19 vaccines, given how their living environments can aid in transmitting the virus, although Friday’s FDA advisory committee did not specify this population in the “high-risk” group for whom booster shots were recommended under emergency use authorization (EUA). However, the FDA and the CDC Advisory Committee on Immunization Practices (ACIP) have yet to make their final recommendations.

Hagan and colleagues examined data from an outbreak at a federal prison involving 233 inmates in two housing units in July 2021. They reported that on July 8, three inmates reported symptoms such as nasal inflammation, cough, headache, myalgia, and rhinorrhea, but were not tested for SARS-CoV-2. On July 12, 18 inmates, including the prior three who reported symptoms, were symptomatic and tested with rapid antigen tests. Eleven of 18 were fully vaccinated.

From July 12 to August 14, all 233 inmates with reported or known exposures were given rapid antigen testing, and some were tested via rapid testing and RT-PCR. A subset of 70 people provided symptom data through questionnaires, and daily nasal swabs for up to 20 days.

Overall, 79% of the 233 inmates were fully vaccinated, and almost three-quarters of all inmates tested positive for SARS-CoV-2.

Within the subgroup, there was no significant difference in median interval between reported symptom onset and last positive RT-PCR test between vaccinated and unvaccinated people (9 vs 11, respectively). Among 58 specimens undergoing genomic sequencing, all were from the Delta variant.

Among fully vaccinated seronegative people, attack rates were significantly higher among those who received Pfizer versus the Moderna vaccine (85% vs 54%, P<0.001). But interestingly, 76% of fully vaccinated inmates who received the Pfizer/BioNTech vaccine were vaccinated at least 4 months prior to the outbreak, while all the fully vaccinated Moderna recipients were vaccinated within 4 months of the outbreak.

“The high number of infections in vaccinated persons, comparable duration of positive RT-PCR test results after symptom onset regardless of vaccination status, and presence of infectious virus in specimens from both unvaccinated and vaccinated infected persons underscore the importance of implementing and maintaining multiple COVID-19 prevention strategies in settings where physical distancing is challenging, even when vaccination coverage is high,” they wrote.