People are more able to fend off coronavirus variants if they have had Covid previously plus a vaccine, new research suggests.
US experts analysed data on people who had recovered from natural infection earlier in the pandemic and found that having a Covid vaccine enabled them to produce high-quality antibodies that could act against variants.
These antibodies were more powerful than those produced by either natural infection or vaccine alone.
The team, from the University of California Los Angeles, said the research suggested booster jabs could help against variants by “improving not only antibody quantity, but also quality”.
The study did not look specifically at the Omicron variant but adds to the body of evidence suggesting existing vaccines and boosters may offer some protection.
Writing in the journal of the American Society For Microbiology, the team said: “We confirmed that some mutations reduce the ability of antibodies to neutralise the spike protein, whether the antibodies were from past infection or vaccination.
“Upon retesting the previously infected persons after vaccination, their antibodies gained the same ability to neutralise mutated spike as the original spike, suggesting that the combination of infection and vaccination drove the production of enhanced antibodies to reach a maximal level of potency.
“Whether this can be accomplished by vaccination alone remains to be determined, but the results suggest that booster vaccinations may help improve efficacy against spike variants through improving not only antibody quantity, but also quality.”
An area of the virus spike protein called the receptor binding domain (RBD) is known to enable the Covid virus to invade a host cell.
This region is also a critical target for antibodies but random mutations in the RBD mean it is an ever-changing target.
In the new study, scientists compared anti-RBD antibodies in the blood of some people to the ability of the antibodies to neutralise the virus.
In people who had never had Covid but who had received a vaccine, antibodies were less effective against mutations in the Beta and Gamma variants than against the original Wuhan strain of the virus.
Similarly, when researchers analysed blood samples from people who had suffered Covid before May 2020 – and before the first confirmation of variants – they had reduced protection against variants.
The experts said this suggests that both mild infection and vaccines produce antibodies that still leave a person vulnerable to new variants.
However, those who suffered Covid before May 2020 and who had a vaccine a year later had antibodies that were just as potent against variants as against the original Wuhan strain.
Immunologist and lead researcher Dr Otto Yang said finding the ideal mix of antibodies could help guide future efforts to tackle Covid-19.