Despite the enormous spread of Covid19, some of us have never been infected, there are several hypotheses to explain the phenomenon, including viral interference.
What is viral interference?
Viral interference refers to the inhibition of the growth of a virus caused by a previous infection. It is a phenomenon still poorly understood and not always present, but for example it could explain why a person who has just recovered from a cold is less likely to contract the flu and vice versa.
We have learned that our immune system is built on multiple levels and has several operating arms: humoral immunity, cell-mediated immunity, innate immunity.
Following the different variants of Sars-CoV2 we have understood the importance of the specific antibodies that our body develops against them, but fortunately we do not have only antibodies available. Over the months we have known the undisputed protagonists of the immune system: T lymphocytes T lymphocytes are less specific than neutralizing antibodies and prevent the virus from causing serious damage that could lead to severe disease or worse death.
There is another layer of the immune system that is unfortunately rarely described: the innate system. The innate immune system comprises a series of cells and mediators that are activated soon after infection and prepare the body to fight against infection.
The innate immune system is much less specific than T lymphocytes and neutralizing antibodies, which is why its post-cold activation provides some sort of protection against the flu.
Not just antibodies, if you get sick less it’s also thanks to killer lymphocytes
by Aureliano Stingi
Does this phenomenon also affect Sars-CoV2?
In a 2021 article, researchers tried to infect human respiratory cells with different viruses to study their dynamics of infection. It was found that an infection with a respiratory virus (those that cause the classic cold) inhibits the growth and proliferation of Sars-Cov2. The first viral infection activates the production of interferon which is a powerful generic antiviral which creates an unfavorable environment for the reproduction of viruses.
In the past we have described the power of interferon in the management of Covid19 and therefore it should not be surprising that this substance produced by our body can inhibit a viral infection.
So a person who has just recovered from a cold could be protected from a new infection caused by Sars-Cov2 thanks to the recent production of interferon that prevents the new virus from ‘taking root’.
The interference is evident
In addition to this possible mechanistic explanation of how the cold keeps SARS-CoV2 at bay (and potentially vice versa), data on the prevalence of the two diseases are accumulating where the phenomenon of interference is evident. If we represent on the same graph the incidence of colds and Sars-CoV2 we can easily observe an anti-correlation, that is where Sars-CoV2 goes up the cold goes down and vice versa. Obviously this could be a spurious correlation that is random and not causal but the experiments described above make us lean towards the second.
Obviously these considerations must in no way induce us to voluntarily contract a cold to be protected from Covid and vice versa, but they are a fundamental piece in understanding the virus and can be exploited to build an even more effective vaccine. In fact, if the vaccine were able to ‘mimic’ the effect of the cold in our body we would not only be protected from serious illness but we would also be immune to contagion.
TAKE HOME MESSAGE
- viral interference is a phenomenon that inhibits the growth of a virus caused by a previous infection
- Viral interference can be observed between flu and cold
- the cold virus inhibits the growth of Sars-Cov2
- the cold virus induces the production of interferons which are potent antivirals
REF:
https://academic.oup.com/jid/article/224/1/31/6179975?login=false#.YG73MQRpEXE.twitter
https://www.nature.com/articles/s41467-021-27674-x.pdf
https://pubmed.ncbi.nlm.nih.gov/33103132
https://www.salute.eu/2022/05/16/news/interferone_covid-349352150/
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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