Vaccines reduce the risk of long COVID by lowering the chances of contracting COVID-19 in the first place. But for those who do experience a breakthrough infection, studies suggest that vaccination might only halve the risk of long COVID — or have no effect on it at all.
The cause of long COVID — also known as the post-acute sequelae of a SARS-CoV-2 infection — is as unclear as its definition. One possibility is that a reservoir of the coronavirus lingers after the acute infection, lurking in various tissues — such as the intestine, liver or brain — and continues to cause damage. Another possibility is that the broad immune response triggered by the initial infection can generate antibodies and other immunological reactions against the body’s own tissues. That could continue to cause complications after the infection has been cleared.
Vaccination could reduce the likelihood of these scenarios. If a vaccine induces high levels of antibodies and T cells capable of recognizing SARS-CoV-2, the immune system could stop the virus during its first few replications before it can establish hidden reservoirs in the body, says Akiko Iwasaki, an immunologist at Yale University in New Haven, Connecticut.
