One variant chasing the other… but this time without necessarily having an impact.
BA.2 is a sub-lineage of the Omicron variant, it is in a way the "little brother" of BA.1, responsible for the very strong fifth wave in December and January.
BA.2 accounted for nearly 30% of daily positive cases in mid-February, according to the latest sequencing survey.
It would now be in the majority but should not lead to a resumption of the epidemic, projects the Institut Pasteur.
The even more reassuring point concerns the risk of a serious form.
BA.1 was significantly less virulent than the Delta variant, predominant until mid-December.
In the event of an infection, various studies have shown that the risk of going to hospital is between 50 and 70% lower.
This made it possible not to exceed the peak of hospitalizations of each of the previous waves this winter, despite a peak of positive cases at least eight times higher.
A reassuring South African study
And BA.2?
It does not seem more virulent than BA.1.
Whether in South Africa, the United Kingdom or Denmark, where it is already the majority, real-life data showed "no difference in severity" between the two sub-lineages, indicated the World Organization. of Health (WHO) on February 22.
A detailed study was conducted in South Africa from December 5, 2021 to the very end of January 2022. According to these results, published on February 19 on the medRxiv platform (but not yet reviewed by peers), the risk hospital admission “did not differ” between people 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, the risk is lower.
BA.2 has crept into 🚨 territory since the Japan lab study is making the rounds…
I wish equal (or more!) attention was given to this real-world population study from SA 🇿🇦 by @nicd_sa which shows NO DIFFERENCE in risk of hospitalization severe disease for BA.2 vs BA.1 pic.twitter.com/rqRFFU0jIC
— 🇺🇦 Meaghan Kall (@kallmemeg) February 19, 2022
The finding is the same for the risk of being severely affected following 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 similar," say the authors, members of the South African National Institute of Communicable Diseases.
The variant “most concerning for global health”?
According to another study, in the United Kingdom this time, BA.2 could even lead to an even lower risk of severe form than BA.1.
After adjustment for age, previous infections, gender, or ethnicity.
The relative risk of hospitalization with BA.2 was 0.87 (confidence interval between 0.75 and 1), according to the report published by the British health agency on Friday.
However, these results are still preliminary and based on a fairly small number of cases, so “it is possible that these estimates will change” thereafter.
Read alsoCovid-19: can you catch Omicron twice?
Finally, note that a Japanese study, not yet reviewed by peers, suggests on the contrary an increased severity with BA.2.
This may "diffuse faster and more efficiently than BA.1 in lung tissue", say the authors, stating that BA.2 may be "the most concerning variant for global health".
But this work was carried out in the laboratory on hamsters, so its results are not necessarily transposable to humans.