A study conducted in the U.K. offers some of the first large-scale, real-world data on how well vaccination protects people against catching a “breakthrough” COVID-19 infection, and how well it protects breakthrough patients from becoming seriously ill. The results are encouraging.
The peer-reviewed study published Wednesday in The Lancet medical journal will help policy makers and epidemiologists fill in a significant gap in the understanding of the true efficacy of three of the major vaccines being used worldwide.
The U.S. Centers for Disease Control and Prevention, for instance, doesn’t have good data on how many people catch COVID-19 after being vaccinated, as it decided in the spring to track only serious, symptomatic breakthrough cases. The British study, on the other hand, used mass-testing data to determine how many breakthrough cases there actually are and how sick those people get.
The vaccines were never intended to prevent infections completely, but to reduce the rates of infection within a population and, most importantly, to reduce the severity of illness in people who do catch it. The study found that people who contracted the coronavirus despite being fully vaccinated were almost twice as likely to have no symptoms at all, compared to the wider population.
Crucially, the odds of a fully-vaccinated person who does catch COIVD-19 ending up hospitalized with severe symptoms were reduced by more than two-thirds compared to an unvaccinated coronavirus patient. The survey also found that the risk of breakthrough patients suffering from long-COVID, with symptoms lasting more than a month, were cut in half by full vaccination.