Saturday 19 June 2021
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Sars-CoV-2 Exposure Immunises; Vaccine Still Needed

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When the war against Sars-CoV-2 began, it became apparent pretty early on that the war would be won when we would be able to develop vaccines against it. The pharmaceutical majors and research laboratories churned out vaccines within an unprecedentedly short period. And once they did, vaccinations began. In the backdrop of doubting murmurs of the effectiveness of the vaccines, vaccinations proceeded. Now, there is evidence emerging that all the work in vaccinating people might have paid off.

A brief note on how vaccines work might be in order here. A vaccine is nothing but a very weak version of a disease-causing cell. So, when the first dose of the vaccine is given, the body can beat this very weak disease-causing cell easily. The body first creates a reactive army of immune cells aimed at neutralizing these disease-causing cells and also create a blueprint of the enemy territory, which it keeps in its memory. The second dose of the vaccine triggers these memory cells and this time, no time is wasted and the immune response is much stronger. Now, the body is prepared to fight the disease mostly for the lifetime of the individual.

This statement of effectiveness of the Sars-CoV-2 vaccine is based on two new studies, which have now offered hope that vaccinations against Sars-CoV-2 might provide lifelong immunity to the virus. If more evidence builds on this emerging story, it could mean that we might not have to line up for yearly booster doses.

This comes in the backdrop of early findings of rapid fall in the blood antibodies in an individual. These studies have shown that upon vaccination or having prior infection with Sars-CoV-2, the memory plasma cells can persist for a year or longer. In addition, vaccinated individuals displayed immunity to the newer strains of the virus, specifically the South African variant. This is a significant finding refuting the argument that previous exposure to Covid-19 precludes Covid-19 survivors from vaccinations.

The first study that was published in Nature involved a study into the blood of 77 Sars-CoV-2 survivors every three months. The study showed that while with time, the levels of antibodies fell in the blood, memory cells in the bone marrow persisted. What this means is that whenever a new Sars-CoV-2 tries to infect the body, these memory cells spring into action, launching an army of antibodies to neutralize the Sars-CoV-2 viruses. These studies have shown that these memory cells persist in a convalescent Covid survivor.

Now, within this group, the bone marrow of 19 unvaccinated Sars-CoV-2 survivors was studied. Of these, 15 showed the presence of memory B cells in the bone marrow seven months post-infection. This means that within 7 months at least if these people had been exposed to a second Sars-CoV-2 infection, the body would have fought the infection back. While this is good news, attention needs to be paid to the 4 individuals in whom no memory B cells were observed. In short, if they would have been exposed to a second Sars-CoV-2 infection post 7 months, they could have been infected again. This is a very important observation as this goes on to indicate that mere infection with Sars-CoV-2 does not remove the need for vaccination, a notion held by many. Irrespective of whether one has had or not has had a Sars-CoV-2 infection, vaccination seems to be the way forward.

In the second study, a group of 63 Sars-CoV-2 survivors were studied, of which 26 members had received at least one dose of either the Pfizer or Moderna vaccine.

Let us concentrate on the members who had received the vaccination first. For these individuals, the memory B cells were able to neutralize a larger population of variants of the Covid-19 virus. This means that when these members are exposed to Sars-CoV-2 viruses, they are able to launch a very strong response and be protected from the symptoms. This is in line with what the previous study had shown.

Now, let us look at what the results were for the remaining 39 members, who had been infected with the SARS CoV-2 virus, but had not gotten vaccinated. For these individuals, the response to the virus was much weaker, especially against the South African variant.

So, what about people who have evaded being infected with the Sars-CoV-2 virus? It is reasonable to assume that they would need both the first and the booster doses of the vaccine since they have not been exposed to the virus earlier. The take-home message is: Yes, we need to get vaccinated, irrespective of whether we have been exposed to Sars-CoV-2 infections or not.

Chaitali Bhattacharjee
PhD in molecular biology, former Young Scientist, working in the life science and healthcare industry since 2007
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