A first vaccine dose after infection with the virus was associated with a 13% decline in the odds of having long COVID and a second shot with a 9% drop in the study published Thursday in the BMJ. Over the course of seven months in 2021, researchers regularly visited the households of more than 28,000 people to ask whether they were experiencing symptoms long after infection.

The findings, together with evidence that long COVID is reduced in those infected after vaccination, suggest that jabs may help decrease the prevalence of persisting symptoms.

“The large scale of this study means that we can be fairly confident about what has been observed, but it does not mean we can be sure what it means,” said Peter English, a former chair of the BMA Public Health Medicine Committee. 

“The most obvious — and perhaps the most likely inference — is that vaccination does prevent at least some cases of long COVID, and may reduce the severity of symptoms,” he said in emailed comments. But “we cannot yet say this with any confidence.” English wasn’t involved in the research. 

An estimated 1.8 million people in the U.K. had reported experiencing long COVID as of April 2022, with two in three people saying the symptoms had affected their day-to-day activities, according to the latest Office for National Statistics data.

The scientists who ran the study called for more research to “understand the biological mechanisms underpinning any improvements in symptoms after vaccination, which may contribute to the development of therapeutics for long COVID.”