Two recent scientific studies have shown that vaccination strategies against COVID-19 may need to change as new variants emerge, though for now authorities will have to make do with the vaccines currently available.
“Ideally, new vaccines should contain the sequence of the variant that’s predominant at the time of administration, however, the variants of this virus are emerging long before a vaccine can be implemented against them,” Balbino Alarcón, lead author of a Spanish study on vaccine efficacy against variants of the COVID-19 virus, told the Spanish television station TeleCinco.
Studies carried out in Spain and the UK and published mid-December showed that the vaccines currently on the market, all made with the original Wuhan COVID-19 strain, provide lower immunity to variants of the virus, particularly Omicron. One study found that vaccinating those who already have antibodies from a past COVID-19 infection can lower their immunity to the various strains that have developed as the virus has mutated.
The Spanish study, done by researchers at Spanish National Research Council (CSIC), measured the reactivity of antibodies from vaccinated people to both the original strain and its first mutation, the alpha strain. They found that antibodies produced by vaccination were relatively less reactive to the alpha variant, especially after the second dose of the vaccine.
As part of their research, they also compared the reactivity of antibodies produced after a naturally occurring infection of COVID-19, to those produced after the same study participants had been vaccinated. They saw that though the first dose of the vaccine did increase the number of antibodies, those antibodies were relatively less reactive to the alpha variant than before the vaccine. The second dose of the vaccine had the “negative counterpart of reducing the relative reactivity of the antibodies” to the alpha strain, though lower reactivity had already been observed after the first dose, the study stated.
Another study done at the University of Oxford examined the efficacy of the Oxford-AstraZeneca and Pfizer vaccines against the Omicron variant compared with previously detected variants. Researchers found that two doses of the vaccine resulted in a “substantial fall in neutralisation” of the Omicron variant, with some samples showing no neutralization at all.
But there is also evidence that a third dose of the vaccines already on the market may still be effective against the Omicron variant.
A preliminary study by the UK Health Security Agency published last week showed that a third dose of COVID-19 vaccines can provide immunity to the Omicron variant. An analysis of 581 participants with confirmed cases of the Omicron variant found that a third dose of the AstraZeneca and Pfizer vaccines rebooted immunity to Omicron, bringing it up to 70%.
The researchers involved in both studies pointed out that their findings are in line with the established science of vaccination—naturally acquired antibodies provide the widest breath of immunity and repeated vaccination with a particular strain of a virus can decrease immunity to other variants.
“Such effect has been observed before, for instance, as a result of vaccination with inactivated influenza virus isolated in immunization campaigns, that result in an efficient neutralization of that particular seasonal variant of influenza but results in reduced capacity to neutralize other variants,” the study stated.
Alarcón recommended serological testing before administering booster shots to decide on the best course for each patient.
Researchers at the CSIC have also developed a simplified serological test that is 99% accurate, according to Alarcón. Recovid Solutions, a specialized diagnostic testing company, also told TeleCinco that it is the only test on the market that can simultaneously determine the presence of three different types of antibodies.
The Oxford researchers concluded that as strains more divergent from the original virus emerge, vaccination for COVID-19 would need to shift to a multi-strain strategy similar to that employed against influenza.