A well being employee collects swab pattern for a COVID-19 take a look at in Jammu on April 8, 2023.
| Picture Credit score: PTI

As COVID-19 circumstances started rising but once more in India in March, many puzzled whether or not the prevailing vaccines, primarily based on the SARS-CoV-2 virus that was first reported in China, would nonetheless be efficient towards newer variations of the identical virus. To reply this query, we have to take a look at a number of primary rules of immunology.

Two-pronged response

Vaccines generate a two-pronged immune response. The primary is the manufacturing of antibodies by B cells, a sort of white blood cells. Antibodies immediately assault and destroy viruses. The second is the T-cell response. T cells are one other sort of white blood cells. They’ve many roles, of which one is to patrol the physique and destroy virus-infected cells. Each these arms additionally give rise to specialised reminiscence cells, that are saved away for future wants.

These two commodities are ‘freshly made’ by our physique following an encounter with the antigen, launched throughout vaccination. Quickly after vaccination, our antibody ranges go up. This offers an early window of safety from an infection. Nevertheless, the degrees of ‘freshly made’ antibodies begin dropping inside three months or so, and ultimately plateau to a low baseline. This low stage is just not sufficient to forestall an infection later.

Why do the degrees drop? It’s pure for the physique to scale down the manufacturing of antibodies after the speedy menace has handed. If this immune contraction didn’t happen, our blood can be as thick as grease from all of the antibodies produced towards each pathogen we’ve encountered in our lives.

The gradual drop within the stage of antibodies is one purpose why folks typically choose up infections regardless of vaccination — this will happen even after receiving a number of booster doses. As an example, in an early evaluation of the XBB.1.16 variant in Pune, India, 26% of the folks had already obtained a 3rd dose.

The opposite purpose is that the virus has altered itself, and among the older antibodies should not capable of lock on to the brand new targets. It isn’t possible to repeatedly give vaccine doses to everybody within the hope that these antibody ranges might be saved excessive. It’s arduous to think about taking a vaccine shot each four-six months. Apart from, there’s proof of a plateauing of the T-cell immune response after repeated vaccine doses. Latest analysis on the most recent variants corresponding to XBB.1.5 reveals virtually no neutralising exercise within the blood six months after a booster dose.

It’s logical to consider updating the first-generation vaccines utilizing elements derived from latest variations of the virus corresponding to Omicron. Sadly, the real-world efficiency of up to date bivalent mRNA boosters has not matched the expectations generated by early laboratory research.

To grasp how antibodies work, it helps to have a look at the barcode on a shampoo bottle at a grocery store. The shampoo is the antigen, whereas the scanner on the checkout is the antibody. The scanner (antibody) recognises the shampoo (antigen) due to the barcode (epitope). Even a tiny alteration within the barcode would imply that the bottle of shampoo will fail to be scanned or recognised. The virus is continually altering the epitopes focused by antibodies. This immune escape is the rationale why new variations of Omicron like XBB.1.16 can simply infect somebody who was contaminated not too way back by earlier variations corresponding to BA.2 and BA.5. Likewise, a T-cell epitope is a particular half (barcode) of the virus protein that’s recognised by our T cells. Not like antibodies that determine giant targets, T cells goal a lot smaller epitopes situated everywhere in the virus, about 15-20 of them, every one being solely eight to fifteen amino acids in size. To change a T-cell epitope is just not a simple job for the virus, as a result of there are about 3,800 base pairs on the spike alone, and about 30,000 for the entire virus.

As every T-cell epitope is of quick size, mutations created by the virus are far too few to alter all of the epitopes on it. If the virus was a e book, antibodies take a look at a complete chapter; T cells take a look at a single sentence. If we modify a number of phrases within the e book, a number of chapters could look totally different, however single sentences are unlikely to be altered. Apart from, particular person HLA variations be sure that every particular person chooses a barely totally different set of T-cell epitopes from a big menu offered by the virus. This primarily implies that the virus can’t idiot everybody abruptly.

T cells to the rescue

In different phrases, the second arm of our immune response stays efficient even towards an altered type of this virus. It’s price noting that T cells don’t cease an infection; they will solely work on viruses which have already entered the cells. Their job is to go looking, discover and destroy virus-infected cells, every certainly one of which is able to in any other case launch tons of or 1000’s of virus copies. By doing this, the unfold of the virus throughout the physique might be halted an organ injury might be restricted. In consequence, vaccinated persons are much less more likely to die even when they obtained contaminated afterwards. Latest analysis has confirmed that T-memory cells stay energetic past two years; the higher restrict is just not recognized but. They’ll rise to the event if and when future infections happen. A straightforward strategy to bear in mind this primary immunology is that antibodies are efficient earlier than the virus enters our cells, whereas T cells come to our rescue after the virus infects our cells. To simplify this additional, to this point the virus has been capable of trick the primary arm of our immune response (antibodies), however not the second.

A wholesome one who has obtained a full dose of the vaccine may have long-term reminiscence generated in each the T-cell and B-cell compartments. Thus, it doesn’t appear obligatory or possible to make a vaccine for each new sub-lineage that comes alongside.

Rajeev Jayadevan is Co-Chairman, Nationwide IMA COVID Job Drive and Previous President, Indian Medical Affiliation