The data included more than 1.2 million adults who reported receiving a first dose of vaccine, and among them, 0.5%, or 6,030, tested positive for a breakthrough coronavirus infection after receiving that first dose. Among nearly 1 million adults who reported receiving a second dose of vaccine, only 0.2% or 2,370 tested positive after completing both doses.
Some groups were more vulnerable to breakthrough infections than others, the researchers found, especially following their first vaccine dose: people 60 and older who were considered frail, and people living in “highly deprived areas,” such as densely populated communities. People who were not obese had lower odds of infection following their first vaccine dose, the data showed.
But overall, the researchers found that being vaccinated was associated with fewer reports of symptoms across all age groups if someone contracted the coronavirus.
Vaccination, compared with no vaccination, was associated with reduced odds of Covid-19 hospitalization or having more than five symptoms in the first week of illness following a first or second dose, the researchers found, and there were reduced odds of long-term symptoms lasting 28 days or more following a second vaccine dose.
“Almost all individual symptoms of COVID-19 were less common in vaccinated versus unvaccinated participants,” the researchers wrote. “More people in the vaccinated than in the unvaccinated groups were completely asymptomatic.”
As for long-term symptoms of Covid-19, some experts not involved in the new study note that there is still much to learn.
“It is however encouraging that the overall proportion of cases with persistent symptoms is reduced in patients that were previously fully vaccinated, which taken together with the milder overall illness and reduction in need for hospital care demonstrates the additional worth of vaccination in reducing severity of illness for individuals,” Ward said, and reducing the burden on health care systems by lowering the number of people needing hospital care.