A study has claimed that the level of protective antibodies falls “quite rapidly” after a patient has been infected with coronavirus.
The fall in immunity could mean that patients are at risk of contracting the virus on several occasions.
Experts have suggested that vaccines would still be effective against the disease despite the apparent drop in immunity.
How long do antibodies stay in a patient’s system?
The new study, from Imperial College London, involved more than 365,000 randomly selected adults who tested 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%, 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.
Would a vaccine still work?
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”.
Asked what the implications were for a vaccine and how long protection from a vaccine may last, he said: “I think that’s an open question that needs to be kept under close research and close scrutiny over the coming weeks and months.
“It’s possible that people might need booster vaccines.
“For some viruses there’s lifelong immunity, for the coronaviruses that doesn’t seem to be the case and we know that you know that that the immunity can fluctuate so, yes, this is something that needs to be looked at very carefully.”
Could the study be flawed?
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.”
How do antibodies work?
Antibodies are a key line of a patient’s defence against the respiratory disease, preventing the virus from getting into the body’s cells.
Antibodies are Y-shaped proteins produced as part of the body’s immune response to infection. They help eliminate disease-causing microbes from the body, for instance by directly destroying them or by blocking them from infecting cells.
Antibodies work by recognising and sticking to specific proteins, such as those found on the surfaces of viruses and bacteria, in a highly specific way. When the body encounters a microbe for the first time, immune cells produce antibodies that specifically recognise proteins associated with that particular microbe.