A study of essential and frontline workers in six US states who tested positive for COVID-19 and received two or three mRNA vaccine doses before Delta infections and three doses before Omicron infections suggests that they had significantly milder infections and lower viral loads than their unvaccinated peers.In the study, published today in JAMA, HEROES-RECOVER Network researchers analyzed the weekly self-collected nasal swabs and whole-genome sequencing results from 1,199 frontline workers infected with COVID-19 from Dec 14, 2020, to Apr 19, 2022, with follow-up until May 9.The workers, primarily healthcare professionals and first responders, were located in Arizona, Florida, Minnesota, Oregon, Texas, and Utah.
Median age was 41 years, 59.5% were women, 72.6% were White, 19.3% were Hispanic, 14% were infected with the wild-type strain, 24.0% had a Delta variant case, and 62.0% had Omicron.More symptom-free days Of the 352 COVID-19 infections among the unvaccinated, 12.5% were asymptomatic, and 6.8% had uncharacteristic symptoms.
Asymptomatic cases were more often linked to Omicron than Delta infections (odds ratio [OR], 5.6).Among participants with symptoms, those with Omicron infections had symptoms for, on average, 12.3 days, compared with 15.6 days with wild-type infections and 16.4 days with Delta.
Omicron-infected participants reported an average of 2.6 days sick in bed, 1.2 days fewer than those with wild-type infections and 2.0 days fewer than those with Delta.