Scientists are investigating whether reservoirs of virus ‘hiding’ in the body are contributing to long Covid.

Earlier this month, Prof David R Walt and colleagues at Harvard Medical School announced that they had detected Sars-CoV-2 proteins – most commonly the viral spike protein – in the blood of 65% of the long Covid patients they tested, up to 12 months after they were first diagnosed.

Walt was motivated to carry out the study after earlier research by his colleagues detected genetic material from the Covid virus (viral RNA) in stool samples from children with multisystem inflammatory syndrome (a rare but serious condition that often strikes around four weeks after catching Covid) as well as spike protein and a marker of gut leakiness in their blood.

If other groups could replicate Walt’s findings, it would be “pretty much game over” for the idea that pockets of the virus were not still present in at least some long Covid patients, said Dr Amy Proal, a microbiologist at the PolyBio Research Foundation, a US nonprofit that supports research into complex chronic inflammatory conditions: “I don’t personally see a mechanism by which the spike protein would be able to persist over long periods of time without the virus [being present].”.

Separate research, which analysed gut tissue from 46 people with inflammatory bowel disease who had recovered from mild Covid, found that viral RNA or proteins could still be detected in 70% of them seven months later.

Even so, definitive proof that viral reservoirs contribute to long Covid is still lacking, and Bhatt would like to see further studies done before reaching this conclusion.