The efficacy of Covid-19 vaccines varies depending on the original strain with which a person was infected, a study suggests.
This discovery means that the way in which an individual's immune system targets and recognises the virus can vary based on their initial exposure.
“There's a notable difference in the focus of immune responses of different people to the Covid virus," Dr Samuel Wilks, from the University of Cambridge’s Centre for Pathogen Evolution, told The National.
“Depending on which variant they first encountered, their immune responses seem to target different specific regions of the virus," he added.
Dr Wilks further explained the practical implications: “If the virus mutates in a particular region, the immune system of some individuals might not effectively recognise the virus, potentially leading to illness.
"Given that there are such differences already after a first infection in the ways in which different immune responses are focused it shows that as new variants continue to emerge we may see mutations appearing that only effect immunity in specific subsets of the human population," he observed.
The study also highlights potential variability in the efficacy of Covid-19 vaccines among individuals. This variability might stem from differences in prior exposures to the virus variants and the consequent immune response.
"Generally, if two variants are close to each other in the map, we would expect that infection with one of the variants would provide good protection against infection from the other. For variants that are further away we would expect less protection," Dr Wilks added.
This new knowledge emphasises the importance of continuing surveillance to identify new variants and understand varying immunity levels to Covid across populations, the researchers said.
Such insights will be crucial for future vaccination strategies, which will need to consider both the specific virus variant within a vaccine and the potential variability in population response.
Different variants
Conducted in collaboration with ten research institutes, including the University of Cambridge, the findings were published in the journal Science.
For this study, 207 serum samples were collected from individuals either naturally infected with different Covid virus variants or vaccinated with the Moderna vaccine.
Notably, the immune responses exhibited marked differences depending on the initial virus variant with which an individual was infected.
Professor Derek Smith, of the University of Cambridge’s Centre for Pathogen Evolution, commented on the study's implications: “These findings enhance our understanding of how future Covid-19 booster vaccines might be refined.”
Dr Wilks said the map helps pick the best vaccine based on how close virus versions are, and since Omicron is very different from earlier versions, past infections don't offer strong protection against it.
"The group with the best protection against the Omicron variants by far was those who had received three vaccine doses," Dr Wilks said.
He also highlighted the need to identify primary virus variants for vaccine development, saying: “Identifying key virus variants for vaccine incorporation is vital for future protection.”
"As we have seen previously for flu vaccination, this simple effect of re-boosting pre-existing immunity seems to be an important effect of having a vaccination, in addition to the new immunity we hope the vaccine will generate, which depends more on the particular choice of variant in the vaccine," Dr Wilks concluded.
Immunity to Covid-19 can be acquired either through natural infection or vaccination.
