Covid-19: what we know about Omicron’s BA.4 and BA.5 sub-variants


Like a shadow on the board. While the decline of the coronavirus epidemic is confirmed in France, with contaminations and hospitalizations on the decline, the certified presence of two new strains of the Omicron variant, the BA.4 and BA.5 sub-variants, puts on alert health authorities.

According to the latest figures from Public Health France, the peak of coronavirus contaminations was reached at the end of March marked by a large domination of the BA.2 sub-variant of Omicron representing 99% of cases in France.

BA.2 is characterized by a very short incubation period, very high contagiousness and a greater capacity for reinfection.

If it is studied closely by scientists, the latter could quickly be monopolized by its “cousins”, the BA.4 and BA.5 sub-variants which are also the subject of increased surveillance.

Sub-variants discovered in mid-December 2021

The two BA.4 and BA.5 subvariants were each discovered in South Africa. Regarding the BA.4, it was identified for the first time in the province of Limpopo in mid-December 2021. As for the BA.5, it was in the administrative capital of the country, in Pretoria, that it was first reported in January 2022.

These two sub-lineages are responsible for an explosion of cases in South Africa.

Currently, the monitoring indicators for the Covid-19 epidemic in the country are close to red with a ratio of 6.3 new cases per 100,000 inhabitants and a positivity rate equivalent to 16.9%.

Data deemed “alarming” by Jacob Lemieux, infectious disease specialist at Massachusetts General Hospital (United States). According to him, these subvariants seem to “cause an exponential increase in positivity rates and already account for more than 50% of cases”.

Cases detected in France

Cases infected with the new strains of Omicron, BA.4 and BA.5, have subsequently been detected in several countries, namely Botswana, the United Kingdom, China, Denmark and even in France.

According to Public Health France (SpF), one case of BA.4 and two cases of BA.5 have thus been identified on French territory as of April 21, 2022.

For its part, the World Health Organization (WHO) has placed these two sub-variants under alert in the “variants of interest” category.

More transmissible and more resistant to vaccines

At this stage, Santé Publique France explains that BA.4 and BA.5 are “quite similar to BA.2 but their Spike protein also has the L452R, F486V and R493Q mutations”.

Concretely, the first mutation (L452R) “is associated with a greater affinity of the virus with the receptor which allows the virus to infect human cells”, explained Dr Antoine Flahault, medical epidemiologist, in an interview with the Dépêche du Noon published this Tuesday, May 3.

“In the end, we may therefore be dealing with a more transmissible variant than Omicron and escaping acquired and vaccine immunity, but not necessarily with a strain associated with greater severity,” he added.

The F486V mutation carried by BA.4 and BA.5 makes it possible to reduce the neutralization of antibodies in the human body. It plays “an important role in vaccine escape. That is to say that the vaccine effectiveness is likely to decrease”, underlines the epidemiologist doctor.



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