THURSDAY, Sept. 2, 2021 (HealthDay News) -- Individuals who have received their COVID-19 vaccination have lower odds of hospitalization and are more likely to be asymptomatic if infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), according to a study published online Sept. 1 in The Lancet Infectious Diseases.
Michela Antonelli, Ph.D., from King's College London, and colleagues conducted a prospective case-control study using self-reported data from U.K.-based adult users of the COVID Symptom Study mobile phone app. Cases had received a first or second dose of the COVID-19 vaccine between Dec. 8, 2020, and July 4, 2021, and had a positive COVID-19 test at least 14 days after their first vaccine dose (before their second dose) or at least seven days after their second vaccine dose (case groups 1 and 2: 6,030 and 2,370 cases, respectively); controls had a negative test (control groups 1 and 2). Participants from case groups 1 and 2 who used the app for at least 14 consecutive days after testing positive were included in the disease profile analysis (case groups 3 and 4: 3,285 and 906 users, respectively) and were matched with controls (control groups 3 and 4).
The researchers found that the odds of infection after the first vaccine dose were higher in older adults (≥60 years) with frailty (odds ratio, 1.93) and for individuals living in highly deprived areas (odds ratio, 1.11); the odds were lower for individuals without obesity (odds ratio, 0.84). In case groups 3 and 4, vaccination was associated with lower odds of hospitalization and having more than five symptoms in the first week of illness following either vaccine dose, and with lower odds of long-duration symptoms after the second dose. Compared with infected unvaccinated individuals, infected vaccinated individuals reported almost all symptoms less frequently; vaccinated individuals were more likely to be completely asymptomatic.
"Our findings might support caution around relaxing physical distancing and other personal protective measures in the post-vaccination era, particularly around frail older adults and individuals living in more deprived areas, even if these individuals are vaccinated, and might have implications for strategies such as booster vaccinations," the authors write.
Several authors are employees of and disclosed financial ties to ZOE, which provided some funding for the study. One author disclosed ties to the pharmaceutical industry.