The Omicron variant of Sars-CoV2 is characterized by a very high contagiousness and according to some estimates it is one of the most contagious viruses ever, but do we really know how many people have been infected?
During the Covid19 epidemic we got used to having a daily and capillary count of all new cases, in fact the end-of-day bulletin updates us on the number of positive swabs and provides us with much more information on the progress of the epidemic. The number of molecular swabs and positive rapid tests is not the only method to know the number of infected people, in fact not all subjects realize they have contracted the virus. The analyzes made a posteriori of the passage of a pathogen are called seroprevalence analyzes: in practice we do not go in search of the live and whole virus but we seek it indirectly, that is through the antibodies produced against it. Serological tests are used to detect the antibodies that our body has produced against different portions of Sars-CoV2.
The seroprevalence analyzes are therefore carried out after the passage of the epidemic wave and are used to confirm or adjust the data detected directly from the positives. These analyzes are very informative because they tell us how efficient the testing system was and can also provide us with information on how symptomatic a variant was.
In fact, particularly severe and symptomatic variants manifest themselves strongly in infected subjects who are pushed to test themselves and therefore result in national reports while less aggressive variants can lead us not to test ourselves and therefore lower the general number of infected.
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Obviously, for logistical reasons, the seroprevalence analyzes are carried out on a random basis and, inevitably, they cannot test the entire population.
We know that the Omicron variant is extremely contagious but fortunately it seems to have a lower virulence than the previous ones, this means that the probability of hospitalization, intensive care and death are reduced. The reduced virulence of Omicron is certainly also due to the immunization campaign that took place in Italy in the last year and a half. Furthermore, the Omicron variant seems to be in line with the previous ones for the number of asymptomatic subjects, in practice about 30% of 100 people who contract Covid19 will be asymptomatic.
So how many people got infected with Omicron?
It is probably impossible to give an exact answer to this question but according to a study published in JAMA last August at least 50% of people did not realize they had contracted Covid19 during the Omicron wave.
The researchers selected a population sample positive for Sars-CoV2 antibodies and of these only half knew they had contracted the virus. To make sure the detected antibodies weren’t vaccine-induced (we know that mRNA vaccines make us produce anti-Spike antibodies), the researchers looked for anti-N antibodies. Protein N is a structural protein of SARS-CoV2 that is not contained in any of the approved vaccines.
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What do these results tell us?
- the Omicron variant has infected far more people than those officially registered
- the Omicron variant in many subjects is totally asymptomatic
- the high number of asymptomatic subjects could facilitate the spread
The fact that the Omicron variant went totally unnoticed in a large portion of the population is good news as it caused no symptoms and disease but at the same time contributed to the very high prevalence of this variant.
REF:
https://www.hindawi.com/journals/bmri/2022/3401566/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9321237/pdf/vaccines-10-01049.pdf
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2795246
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
Instagram: Aureliano _Turn off Twitter: @AurelianoStingi