COVID antibody levels fall “quite rapidly” after coronavirus infection, researchers have found, meaning immunity may not last long and reinfection rates may increase.

Scientists leading the study say vaccines against Covid-19 could still be effective despite the new findings. 

The Imperial College London study saw more than 365,000 randomly selected adults test themselves at home using a finger prick test to check if they had antibodies against Covid-19.

Over this period, the proportion of people who tested positive for Covid-19 antibodies declined by 26.5 per cent, suggesting antibodies reduce in the weeks or months after a person is infected.

Experts leading the Real-Time Assessment of Community Transmission (React-2) study said the findings suggested immunity was “waning quite rapidly”, which could lead to an increased risk of reinfection.

However, Professor Wendy Barclay from Imperial, who worked on the study, said there was still reason to be optimistic about a vaccine being able to stimulate longer-lasting protection.

She told Times Radio on Tuesday: “I think that we can still continue to be optimistic about vaccines because vaccines will work in a different way.

“What we’re measuring at the moment is the way that our bodies’ immune response reacts to the virus infecting us.

“But when we immunise with vaccines, particularly the new generation of vaccines that have been developed and put forward into trials for Sars-CoV-2, the virus that causes Covid, they work in quite different ways and they might make an immune response which is much more long lasting than natural infection.

“So we have to keep optimistic about that.”

Professor Paul Elliott, director of the React programme and also from Imperial, told BBC Radio 4’s Today programme that a vaccine response may behave differently to the response to natural infection.

He also said some people may need booster vaccines. 

Healthcare workers were found to have higher levels of antibodies in the study, as did people living in large households and those from black, Asian and minority ethnic backgrounds.

Dr Alexander Edwards, associate professor in biomedical technology at the University of Reading, said the rapid home tests used in the study are generally only “able to detect only high levels of antibody”.

He said other lab-based tests can detect really low levels of antibodies, adding: “When people are ill, antibody levels rise, and when you heal, antibody levels do drop naturally – this is not exactly the same as losing immunity.

“What is not clear is how quickly antibody levels would rise again if a person encounters the Sars-CoV-2 virus a second time.

“It is possible they will still rapidly respond, and either have a milder illness, or remain protected through immune memory.

“So even if the rapid antibody test is no longer positive, the person may still be protected from re-infection.

“But we don’t know this yet, it takes time to work this out, by following large groups over many months, and this type of study is ongoing yet hard and slow.”