Singapore is facing a resurgence of the Covid-19 outbreak, driven by the XBB subvariant. A mutation of the coronavirus that would not cause more serious illness than the other variants.
The sub-variant of Omicron, called XBB, has been emerging for several weeks in certain Asian countries, such as Singapore and Bangladesh.
XBB is a sub-variant of Omicron which was detected at the end of 2021. Although it is more contagious than Delta, it is also less virulent than the latter. More specifically, XBB is a recombinant, that is, a variant that has been created by combining the genetic material of two different variants. In this case, strains BJ.1 and BA.2.75, themselves sub-variants of Omicron.
Where does it emerge?
In recent weeks, XBB has led to an upsurge in the Covid-19 outbreak in Singapore. The Ministry of Health said that the country had more than 6,800 cases of Covid-19 on Wednesday on a sliding average over 7 days, compared to less than 3,000 at the end of September.
This new subvariant has also been detected in Bangladesh, Denmark, United Kingdom, Australia, Belgium and Austria.
Despite this resurgence of the epidemic, “the number of serious cases has remained relatively low” and there is “no evidence that XBB causes a more serious disease”, wanted to put the Singaporean Ministry of Health into perspective on Tuesday.
“This is most likely due to resistance built up by vaccination and previous waves of infection,” he added.
Are vaccines still effective?
Faced with the resurgence of the epidemic, Singapore has decided to administer from Friday the bivalent vaccine designed by Moderna and Spikevax, which specifically targets the Omicron vaccine, to certain categories of people, such as those aged 50 and over.
Four variant-containing mRNA vaccines, which include Omicron BA.1 or BA.4/5 subvariants to the original virus, have been licensed for use as booster doses. However, these vaccines can only offer a “tiny additional benefit”, however, the group of experts who advise the World Health Organization on vaccination said on Wednesday.
“The currently available data are not sufficient to support making a recommendation in favor of booster doses containing bivalent variants” compared to vaccine doses based on the original virus, he said in a statement.
According to a study conducted by Chinese scientists, pre-published on October 4 and which has not yet been peer-reviewed, the recombinant XBB would be particularly resistant to antibodies. According to this study, this would mean that “booster vaccines designed on the basis of BA.5” – which is also a sub-variant of Omicron – “may not provide broad-spectrum protection against infection”.
The Omicron variant accounted for 99.9% of virus samples collected and sequenced as part of the global science initiative GISAID over the past 30 days. Among them, the BA.5 group of Omicron subvariants remained overall dominant at 81%, followed by the BA.4 mutation at 8% and the BA.2 subvariant at 3%.