Odds of developing long COVID halved after vaccination, study finds
They also reported a rate of breakthrough infections among fully vaccinated people that was well below 1%.
The findings are from a prospective study that used self-reported data submitted to a cell phone app by adults in the United Kingdom who received either a first or second COVID-19 vaccine dose between Dec. 8, 2020, and July 4, 2021.
During the study period, more than 1.24 million app users reported that they received at least one dose of a COVID-19 vaccine, and more than 971,000 reported receiving two doses, according to Michela Antonelli, PhD, a senior research associate at King’s College London, and colleagues.
Via the app, 6,030 people (0.5%) reported receiving a positive COVID-19 test at least 14 days after their first vaccine dose but before receiving a second dose, and 2,370 people (0.2%) who received two doses reported having a positive COVID-19 test at least 7 days after completing the vaccine, the researchers reported. Study participants were infected with SARS-CoV-2 a mean of 73 days after receiving a first dose and 51 days after receiving their second dose.
The authors reported finding a “significant inverse association between age and post-vaccination infection that was more evident in older adults” after one dose (OR = 0.94 per year increase in age; 95% CI, 0.93-0.95) and two doses (OR = 0.93; 95% CI, 0.92-0.95).
The odds of experiencing symptoms 28 days or more following initial infection were 49% lower if participants had received both doses of a vaccine (OR = 0.51; 95% CI, 0.32-0.82).
Moreover, “Compared with unvaccinated controls, individuals after their first or second vaccine dose were less likely to have more than five symptoms in the first week of illness or present to hospital, and were more likely to be completely asymptomatic,” the authors wrote.
Among those aged 60 years or older, frailty was associated with having a higher risk for post-vaccination infection after receiving one dose (OR = 1.93; 95% CI, 1.5-2.48).
“Frail adults in long-term care facilities are at particular risk of transmitting respiratory illness, and have been disproportionately affected throughout the COVID-19 pandemic,” the authors wrote.