(Sarah Reardon/ Scientific American) — Vaccination against SARS-CoV-2 lowers the risk of long COVID after infection by only about 15%, according to a study of more than 13 million people1. That’s the largest cohort that has yet been used to examine how much vaccines protect against the condition, but it is unlikely to end the uncertainty.
Long COVID — illness that persists for weeks or months after infection with SARS-CoV-2 — has proved difficult to study, not least because the array of symptoms makes it hard to define. Even finding out how common it is has been challenging.
Some studies have suggested that it occurs in as many as 30% of people infected with the virus. But a November study of about 4.5 million people treated at US Department of Veterans Affairs (VA) hospitals suggests that the number is 7% overall and lower than that for those who were not hospitalized. (…)