People who’ve had Covid but no jabs may have longer immunity than those who’ve been double-jabbed but never infected, a study suggests.
There has been fierce debate about whether natural or vaccine-induced protection is better throughout the pandemic, with research producing mixed results.
The debate has become more complicated as time has gone on because so many people have both been exposed to the virus and had their shots.
The latest study — from Israel — followed more than 500 people who had either just caught the virus or had recently received two jabs between 2020 and 2021.
Participants were tracked for up to a year and given regular blood tests measuring their antibody levels and strength of protection.
While those who were vaccinated had higher levels of antibodies initially, they dropped off much sharper than in the natural infection group.
After six months, the prior-infection group also had ‘stronger’ antibodies — a measure of how well they bind to Covid’s spike protein when the virus enters the body.
Experts said the ‘jury is still out’ on which type of immunity is better, but almost all scientists agree that a combination of vaccine and natural protection is the best.
The study — led by the Sheba Medical Center in Ramat Gan — only looked at antibodies, which is one part of the complex immune response to Covid.
Immunity also involves T-cells and other white blood cells that are harder to measure but can provide longer lasting protection — especially against severe outcomes.
The research was also carried out when the original Wuhan and Alpha strains were dominant in Israel, so the findings may not necessarily reflect immunity against later variants like Omicron.
But a study by Maccabi Healthcare and Tel Aviv University in Israel last August also found that natural immunity was better at preventing infection from the Delta variant — by up to 13 times.
In the latest study, none of those who were infected originally became re-infected during the study and those who were jabbed did not get the virus afterwards, suggesting both had high levels of immunity throughout.
The experts recruited 130 people who were infected between March and November 2020 and did not go on to get vaccinated by April 2021.
They also studied 402 people who got their second jab in late 2020 but had never had an infection.
Israel led the world with its vaccine rollout at the time.
The experts measured antibody levels in patients’ blood stream immediately after infection or the vaccines, and did follow-up tests after six months.
The researchers also measured antibody avidity — how well the infection-fighting proteins attach to the target virus.
Those who were vaccinated initially saw a higher level of antibodies as well as higher avidity.
But after six months, the ‘never-Covid’ group saw both measures fall to lower levels than the unvaccinated cohort.
Meanwhile those who were infected saw their antibody levels fall more gradually.
Avidity actually appeared increased after six months, although the researchers cannot explain why.
The findings are due to be presented to the European Congress of Clinical Microbiology & Infectious Diseases conference in Lisbon, Portugal, in April.
Writing in the study, the researchers said: ‘While the number of antibodies decrease with time in both Covid recovered (but never vaccinated) patients and vaccinated (but never infected) individuals, the quality of antibodies increases following infection but not after vaccination.’
They said future research should look into whether people infected with previous variants still have greater protection against Omicron.
Dr Carmit Cohen, an epidemiologist at the Sheba Medical Center who led the report, said: ‘With the omicron variant vaccinated individuals are better protected from severe disease.
‘I think that the most interesting people to follow up now are those who have recovered from the earlier variants and have then been reinfected by, and recovered from, infection with the Omicron variant.
‘Hypothetically, these individuals should have very high antibody performance against most variants.’
Independent experts said the ‘jury is still out’ on whether natural immunity offers stronger protection against the virus.