Before I go further I want to emphasise that the research study I refer to is not an excuse to refuse vaccination: not everyone has the pre-existing immunity (obviously!).

The idea of exposure to a harmless virus providing protection to a harmful goes back to the first vaccines when deliberate infection with the cowpox virus provided immunity from smallpox. Very early in the pandemic there was speculation that exposure to other cornaviruses might provide protection against SARS-CoV-2. The pre-publication study by teams from several major research groups on the Nature site found that a small proportion had such protection.

The scientists were closely monitoring hospital staff during the first wave of the pandemic – including by taking regular blood samples.

Despite being in a high-risk environment, not everyone in the study came down with Covid. The results, published in the journal Nature, showed some people just managed to avoid the virus.

But around one-in-10 had signs of being exposed, but never had symptoms, never tested positive and never developed Covid-fighting antibodies in their blood.

Part of their immune system was able to get on top of the virus before it managed to take hold – what’s known as an “abortive infection”.…

To understand what is happening we have to look at the body’s immune responses to viruses and the specifics of the COVID-causing virus.

When an viral infection challenges the body the immune system responds. We are familiar with the idea that antibodies are produced to neutralise the antigen (the virus). There are a number of other responses including the production of “memory T” cells among others. The antibodies fade over time but these other responses “train” the immune system to produce the right antibodies etc to either stop (“abort” ) infection or make any disease caused by the virus milder.

Another buzz-word we are all too familiar with is the “spike protein”. The picture shows these as the red floret-like structures on the surface of the virus. The purpose of these are to be able to attach to the cell membrane and open a route for the virus’s RNA to pass from its protective “corona” into the cell and infect it.

The COVID vaccines and antibody tests target this spike protein, or rather sections of it. The vaccine stimulates the body to produces antibodies that “clog up” the spike and generate the other immune responses but only to the spike protein. An  infection by SARS-CoV-2 also generates these responses to the other parts of the virus like the shell and the RNA nucleus. There are 27 other proteins beside the spike.

Animal cells are quite bad at replicating RNA viruses as most do not have a “spellcheck” mechanism. To quote an old joke, they play “all the right notes but not necessarily in the right order”, although a few bum notes are also played. Large numbers of different variations can be expected. Some mutations will render the virus unable to infect. Some will give it a competitive advantage against earlier versions, as we have seen with the Alpha and Delta variants. Some will enable the virus to attach to and infect the cells of different species from the original host in which it may or may not produce disease.The AstraZeneca vaccine for example is based on a chimp flu virus that is harmless to humans.

As the BBC article points out

These internal proteins are very similar in all related species of coronavirus, including the ones that are widespread and cause common cold symptoms.

It means targeting these proteins with a vaccine could give some protection against all coronaviruses and new Covid variants.

The team said the current vaccines were doing an excellent job of preventing people from becoming severely ill, but were not as good at stopping them catching Covid.

The hope is that vaccines to target other parts of the virus will stop infection in the first place. The healthcare workers in the subject group have likely been exposed to wide range of other human viruses including the four coronaviruses that cause the common cold. Domestic pets and farm animals also  harbour their own coronaviruses.

The COVID-19  pandemic has been traumatic for many countries but the understanding of viruses in general has developed and the knowledge will aid fighting future emergent diseases.

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This is a Creative Commons article. The original version of this article appeared here.


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