Soon after the vaccination campaign began in many countries, the arrival of faster-spreading Covid variants triggered fears that these could evade vaccines. The good news comes from the initial studies: they suggest that existing vaccines will still work. The bad news is that they may be slightly less effective against two variants: the South African and the Brazilian one.
“I'm optimistic that the current vaccines will remain quite useful,” he says Jesse bloom from the Fred Hutchinson Cancer Research Center in Seattle. “But I expect that eventually it will be necessary to update the vaccines to take into account viral evolution and Covid variants.”
Antibodies are our main defense against viruses. When we become infected with a new virus, our immune system begins to produce a series of antibodies that bind to various parts of the viral proteins.
Not all antibodies are the same. Studies show that only a few antibodies can “neutralize” viruses and prevent infections. These neutralizing antibodies bind to key sites on viral proteins.
What happens in the case of the Covid variants
For the coronavirus, one of these antibody “target” sites is the part of its so-called Spike protein, the one that binds to receptors on human cells and helps the virus enter. If this part of the protein changes, neutralizing antibodies may also fail to bind.
B.1.1.7, or “English Covid variant”: MINIMUM drop in effectiveness
One of the fast spreading Covid variants called B.1.1.7, first identified in the UK, it has only one mutation affecting this type of link. Initial antibody studies of those previously infected with the coronavirus or treated with the Pfizer and BioNTech vaccine show little or no decrease in effectiveness against B.1.1.7.
B.1.351, or “South African variant”, and “Brazilian variant”: they are worrying
The “Brazilian” P.1 and “South African” Covid variants, B.1.351, are more worrying. They have almost the same three mutations in the binding domain. According to a computer model , the spread of B.1.351 can be explained by the fact that this variant it is 50% more transmissible or 20% better at evading immunity in previously infected people, compared to previous Covid variants. Laboratory studies point to the latter.
Bloom and his team have tested how mutations in the binding domain alter the effectiveness of antibodies from people who have been infected with the coronavirus. Mutations at the E484 site made the biggest difference, with neutralizing activity it decreased up to tenfold.
Further evidence of the possibility of reinfection
Further evidence comes from a study by Rino Rappuoli. Rappuoli is the "father" of some vaccines (including the one for Meningococcal B), chief scientist of GSK Vaccines in Siena, and coordinator of the Monoclonal Antibody Discovery (Mad) Lab of Fondazione Toscana Life Sciences. When his team developed the virus in the presence of antibodies from a previously infected person, E484K was one of the three mutations which allowed the virus to become resistant. Results that suggest that the spread of B.1.351 is due to the E484K mutation which helps the virus evade antibodies and reinfect people who have already had Covid. “Whether beyond this they are more contagious, I don't know,” says Rappuoli.
What should we expect?
Although the early data on these two Covid variants sounds alarming, the current vaccines have such high efficacy, even 95%, that even a large drop in neutralization may not substantially reduce protection, Bloom says. Antibodies may not be as effective, but they still get the job done.
Yet: there have, it is true, reports of reinfections in South Africa. The government epidemiologist reports it to you Salim Abdul Karim in an online presentation. There was also a report of a woman in Brazil who had more severe symptoms the second time. But such anecdotal reports are to be expected, Karim says, and in South Africa there is no evidence of a systematic increase in reinfections.
It may be because testing the effectiveness of antibodies outside the body doesn't tell the whole story. The so-called T-cell response is also important: T cells detect an infected cell by detecting viral proteins on its surface and then destroy it before it releases more viruses.
“T cells can be incredibly valuable in preventing disease,” he says Shane Crotty from the La Jolla Institute for Immunology in California. “They can do it so well that the person never gets sick.” Crucially, an effective T cell response requires only the recognition of viral proteins, rather than blocking their function. The T cell response to the coronavirus is broad and involves many parts of the spike protein and other proteins. “There's no way these Covid variants are escaping T-cell immunity,” Crotty says. Unfortunately, while T cells can prevent people from experiencing symptoms, they cannot prevent infections.
In short (Italian only)
Existing vaccines should still protect against the B.1.351 and P.1 Covid variants, but may be slightly less effective. And there is a danger that these Covid variants or others will evolve further to be even better at evading vaccine protection.
This means we need to step up surveillance so we can detect these Covid variants early and have time to update vaccines, he says. Angela Rasmussen of Georgetown University in Washington DC.
It is unlikely that a variant will emerge overnight that can completely evade the vaccine. But if we don't look for it and keep watch, we may not find it until it's too late.
Angela Rasmussen, Georgetown University
Covid variants: how to possibly update vaccines
Scientists are already studying how to update the vaccines (much like what happens with the current seasonal flu vaccines) and it seems it will be relatively easy to do so. The main delay could be getting approval – updated flu vaccines don't have to go through clinical trials, could a similar process apply? “I think it can be done very quickly,” says Rappuoli.
