According to many researchers and experts, Sars-CoV2 will not stop circulating in the short term and it is likely that we will become infected several times in the coming years. But what do we know about re-infections? Are they dangerous? Are the symptoms of re-infections increasingly mild or can they be dangerous? Let’s clarify.
Covid-19 is a disease that has different effects on different people
The most immediate and correct answer to these questions would be: “it depends”. We have learned that Covid19 is an extremely heterogeneous disease and its effects can be devastating for some individuals and virtually invisible for others. So for the single individual we will never be able to know exactly what his response will be to the first infection or to re-infections but we can observe the population and estimate what happens on average in the various categories. Before analyzing the responses of the population to re-infections, let us analyze the phenomenon from a biological and immune point of view.
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The immune system and the virus
Our adaptive immune system, i.e. the arm made up of antibodies, B lymphocytes and T lymphocytes is strengthened with repeated stimulation. In practice, repeated exposures to the same antigen (a part of a virus) stimulate the production of T lymphocytes and specific antibodies against it. This mechanism is exploited by vaccines, in fact it is not uncommon to receive several boosters of the same vaccine. Boosters are nothing more than different exposures of the viral antigen. (Even if the adaptive immune system works for repeated stimulation it is never advisable to voluntarily expose yourself to contagion)
The Coronavirus family
The adaptive immune system in general works like this, but let’s see in detail how it works against Coronaviruses. Coronaviruses are a family of viruses (to which Sars-CoV2 also belongs) that cause mild illnesses such as seasonal colds. Recent work has shown that immunity to Coronaviruses is established after numerous re-infections that occurred in childhood. We know that children are particularly exposed to microbes and pathogens, in fact they are often ill. The numerous interactions with Coronaviruses during childhood create an immune memory which is then maintained as adults, in fact for adults Coronaviruses cause at most colds.
So will re-infections with Sars-CoV2 have the same effect as re-infections with Coronaviruses?
We cannot know, but we can analyze what has happened so far.
For convenience, let’s analyze the outcome of re-infections in vaccinated and recovered subjects (or recovered and then vaccinated), in these subjects on average we observe a:
- reduction in the risk of death
- reduction of the risk of hospitalization
- reduction in intensity of symptoms
How are these data interpreted? It means that the probability of death in case of Covid19 in a healed and vaccinated subject is lower than that of a healed or vaccinated subject only.
Simplifying we can say that on average a vaccinated and recovered subject who becomes reinfected should not experience more severe symptoms.
This trend shouldn’t surprise us because from a purely biological point of view this is exactly how our immune system works.
But is this always true for everyone? No
Some groups of people could still experience more severe or even lethal symptoms, and let’s remember that not everyone responds to the vaccine in the same way. Frail or elderly subjects with various pathologies risk negative consequences regardless of the number of re-infections.
As far as long-term consequences and Long Covid are concerned, unfortunately there is still no robust literature on re-infections but the vaccine seems to offer some protection against the risk of developing Long Covid.
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TAKE HOME MESSAGE
- re-infections with Covid19 tend to be less severe and protect us from severe symptoms, hospitalization and death
- Covid19 is an extremely HETEROGENEOUS disease in the population
- it is difficult to estimate the effect of re-infection on an individual
- despite the observed trend it is better to avoid re-infections
REF:
https://www.newyorker.com/science/annals-of-medicine/how-many-times-will-you-get-covid
https://www.thelancet.com/journals/lansea/article/PIIS2772-3682(22)00028-2/fulltext
https://www.medrxiv.org/content/10.1101/2022.10.31.22281756v1.full.pdf
https://www.nejm.org/doi/full/10.1056/NEJMc2200133
https://assets.researchsquare.com/files/rs-2082030/v1/35f83199-0425-4b81-8e3d-4e69d2088bfc.pdf?c=1666882967
https://www.nejm.org/doi/full/10.1056/NEJMc2200133
https://www.sciencedirect.com/science/article/pii/S1931312822003584
Aureliano Stingi, doctor in molecular biology works in the field of precision oncology. He collaborates with the World Health Organization in the battle against Covid19-themed fake news
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