COVID-19: Reassuring data on the risk of a severe form with BA.2, a subtype of Omicron

One version is following the other… but this time to no avail. BA.2 is a subgenre of the Omicron variant, it is in a way a “little brother” of BA.1, which is responsible for the very strong fifth wave in December and January. According to the latest sequencing survey, BA.2 accounted for around 30% of daily positive cases in mid-February. It will now be in the majority, but should not restart the pandemic, projects Institut Pasteur.

An even more reassuring point concerns the risk of a serious form. BA.1 was significantly less toxic than the delta variant, which was dominant by mid-December. In the event of infection, various studies have shown that the risk of hospitalization is between 50 and 70%. This made it possible not to exceed the peak of hospitalizations in each of the previous waves this winter, despite the number of positive cases being at least eight times higher.

A Reassuring South African Study

and B.A.2? It doesn’t seem more viral than BA.1. Whether in South Africa, the United Kingdom or Denmark, where it is already a majority, real-life data showed “no difference in severity” between the two sub-lineages, the World Health Organization (WHO) indicated on 22 February. .

A detailed study was conducted in South Africa from December 5, 2021 to the end of January 2022. According to these results, published on the medRxiv platform on February 19 (but not yet peer-reviewed by peers), the risk of hospital admission “was not the difference between those infected with BA.1 and those who caught BA.2”. The relative risk was 0.96, with a confidence interval between 0.85 and 1.09. If it is below 1 then the risk is low.

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The finding is similar for the risk of being seriously affected after hospitalization (relative risk of 0.91, confidence interval between 0.68 and 1.22). These results were adjusted for comorbidities to avoid bias. They “suggest that although BA.2 may have a competitive advantage over BA.1, the clinical profile of the disease remains the same,” say the authors, a member of the South African National Institute of Communicable Diseases.

Edition “Most relevant to global health”?

According to another study, this time in the United Kingdom, BA.2 may pose an even lower risk of the severe form than BA.1. After adjusting for age, previous infection, gender, or ethnicity. According to the report published on Friday by the British Health Agency, the relative risk of hospitalization with BA.2 was 0.87 (confidence interval between 0.75 and 1). However, these results are still preliminary and based on a small number of cases, so “it is possible that these estimates will change” thereafter.

Finally, note that a Japanese study, which has not yet been peer-reviewed, in contrast suggests an increased severity with BA. It can “disseminate faster and more efficiently than BA.1 in lung tissue”, the authors say, adding that BA.2 may be the “most concerning type for global health”. But the work was done on hamsters in the lab, so the results are not necessarily applicable to humans.

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