One of the dominant questions today following the detection of Omicron variant of SARS-CoV-2, which causes Covid-19, is whether vaccine will work against the newly detected coronavirus variant or not. This is an intriguing question as most Covid-19 vaccines are two-dose regime, and a large number of people are partially vaccinated.
To understand this situation, let’s first see how vaccines work against SARS-CoV-2. Most vaccines target the spike protein area of the virus. It is that part of the coronavirus that it uses to enter a human cell.
Vaccines work by training the human’s immune system to identify the spike protein of SARS-CoV-2 and attack it when the virus tries to enter the body.
What has been seen in the Omicron variant is that its spike protein has more than 30 mutations. Ten of these mutations have been seen in what is called the receptor-binding domain or RBD of the spike protein. The RBD is that part of the spike protein which latches on to a human cell. A highly mutated RBD can carry the Omicron variant undetected by the body’s immunity.
However, spike proteins are not the only part of the coronavirus that the immune system identifies and can target. Antibodies and T cells specific cells that grow in the body in response to previous infection or vaccination and are capable of memorising the pathogens can still offer protection against a mutated SARS-CoV-2. This holds true even for the Omicron variant.
The UK-based newspaper, The Guardian quoted Danny Altmann, professor of immunology at Imperial College London, as saying, “If you scribble the mutations on to a picture of the spike protein’s crystal structure, and relate that to all of the main antibody activities that we know about, it looks kind of terrifying like, most of your key, neutralising antibody targets will be shot to pieces, so what’s going to be left of your immune protection?”
“And yet, the soundings we’re getting from South Africa seem to be saying that it doesn’t look severe, and the people who are going to hospital are the unvaccinated, rather than the vaccinated, as if vaccination was still buying [them] some cover.”
“We all think that the T cells can see the differences [between variants], and that the T cell repertoire is much more impervious to it, so that might also buy you some protection.”
In the case of vaccinated yet infected with Delta variant, the Covid-19 patients were reported to have nine times less likely to die. Fully vaccinated people were also said to have three times lower chances of catching infection compared to those unvaccinated.
The Guardian quoted another expert, Cardiff University’s immunologist Prof Paul Morgan, as saying that although the Omicron variant looks more infectious “a blunting rather than a complete loss [of immunity] is the most likely outcome.”
“The virus can’t possibly lose every single epitope [areas on virus which antibodies and T cells can target] on its surface, because if it did that spike protein couldn’t work anymore. So, while some of the antibodies and T cell clones made against earlier versions of the virus, or against the vaccines may not be effective, there will be others, which will remain effective.”
In case of fully vaccinated people, who were infected with Delta variant, the protection appears to have been better. University of Bristol’s virology professor David Matthews told The Guardian, “If you’ve been double-jabbed and then infected with Delta and recovered, then you have got a very broad, very effective immune response, that probably covers pretty much any variant that you can think of.”
The reason is very simple. Such individuals were vaccinated against the original virus that broke out Covid-19 in China’s Wuhan and they also developed natural immunity due to mutant Delta variant.
“It means you’ve got an antibody response that covers both classic and modern strains and a very broad T cell response, not just against the spike protein, but against all the other proteins that Sars-CoV-2 makes and that’s incredibly helpful,” Matthews said.
The real worry remains for those unvaccinated. They don’t have natural or vaccinated immunity against the Omicron variant, which is said to be more infectious.
Experts say that if the Omicron variant spreads at a faster rate as is being anticipated, this virus may infect more and more unvaccinated people leading to a possible higher hospitalisation.