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The risk of long covid may be considerably lower in people who catch the coronavirus after being vaccinated.

at the UK鈥檚 Office for National Statistics (ONS) and his colleagues looked at a random sample of people, aged 19 to 69, who tested positive for the coronavirus between April 2020 and November 2021.

The sample included 3090 people who had received a second dose of either the Pfizer/BioNTech, Moderna or Oxford/AstraZeneca coronavirus vaccine at least two weeks before they first tested positive for the virus.

These participants were paired up with a random sample of 3090 unvaccinated people, with the individuals being matched by their age, sex, socioeconomic status, any pre-existing health conditions and whether they were white or a different ethnicity. The sample size was too small to group the participants according to more specific individual ethnicities, says co-author .

All the participants were part of the , which involved them being regularly tested for the coronavirus and self-reporting any long covid symptoms.

The researchers defined long covid as any symptom a participant reported at a follow-up appointment 12 weeks after testing positive, with the participant only being able to explain the symptom as being due to the coronavirus.

Of the unvaccinated participants, 14.6 per cent reported having at least one long covid symptom 12 weeks after their infection, compared with 9.5 per cent of those who were vaccinated before catching the coronavirus.

The risk of having long covid at 12 weeks post-infection was 41 per cent lower in the vaccinated individuals. The longer-term risk wasn鈥檛 explored in the study, with past research suggesting long covid can persist for more than a year.

According to Ayoubkhani, a major limitation of the study is that the two groups of participants were largely infected by two different coronavirus variants. Most of the vaccinated participants were infected when the delta variant was dominant, whereas most of the unvaccinated people probably caught the alpha variant, he says.

In addition, the study didn鈥檛 analyse the prevalence of long covid in people who first caught the coronavirus when the omicron variant was dominant.聽 鈥淔rom other studies we鈥檝e published at the ONS we know that if you鈥檙e double-vaccinated, the risk of long covid at 12 weeks after BA.1 or BA.2 [omicron subvariants] is about half that compared with delta,鈥� says Ayoubkhani.

The researchers didn鈥檛 see any difference in long covid severity between the vaccinated and unvaccinated groups.

鈥淚 think the findings are interesting and are consistent with the emerging literature on the topic,鈥� says at Bar Ilan University in Israel. 鈥淭he question is now less about if vaccination reduces long-term symptoms but why and how much.鈥�

鈥淚 do firmly believe that vaccines reduce the risk of serious illness during covid and subsequently long covid based on current evidence,鈥� says at the University of Michigan.