The Mu variant seemed to have all the credentials to represent a danger. Emerged in January 2021 in Colombia, by September it had already spread to 39 countries, reaching North America, Europe, Asia and the African continent. Some characteristics of the virus also indicated a high ability to evade the defenses created by vaccines and previous infections.
Mu listed among the variants of interest
There were every reason to worry, in short, and for this reason WHO decided in September to include it in the list of variants of interest, to be kept under control as potential dangers for the future. Then suddenly Mu disappeared. In October the new cases were in free fall, in December there were no more cases, and in March of this year it was declared no longer in circulation. A little epidemiological mystery, which a new study just published on Jama Network Open helps clarify today.
Variant Xe, 10% more contagious: what we know
by Donatella Zorzetto
The Colombian study
The study, carried out by a consortium of Colombian research institutes, mapped the spread of Sars-Cov-2 variants in the country between July 2020 and August 2021. Collecting information on patients, their age, gender and possible presence of risk factors. Thanks to this database, it returns a reliable picture of the epidemiological trend of the new Mu variant from its first appearance in the country, in January 2021, until August, when its decline began.
The data show that the virus had a certain ability to cause severe symptoms, even in people relatively without risk factors: 71% of patients with a confirmed infection with the Mu variant did not have any comorbidities, against an average of 66 % recorded for all other variants, and 69.2% emerged for a virus as dangerous as the Delta variant.
Mortality among patients with confirmed infection was also relatively high, reaching 11.7%, compared to 9.4% for the “variants of concern” (including Delta).
Coronavirus next coming: here are which variants we must be afraid of
by Noemi Penna
The decline started in August
Looking at the epidemiological scenario, in just two months Mu represented about 25% of the samples analyzed. In May, almost 50%, and in July, corresponding to the highest peak of infections recorded in the area, it had reached 85%. By August, however, it was already decreasing, and in the following months it would disappear, while a new variant made its way into Colombia: the Delta variant.
Faced with severe symptoms and a high ability to reinfect patients recovered from the disease (as evidenced by the peak of cases in July, in a period in which a high percentage of the population had previously contracted Covid 19), Mu si thus revealed unable to compete with Delta, a much more infectious variant, the spread of which has prompted Mu to disappear in Colombia, and in the rest of the world.
Covid: Deltamicron check, the hybrid and very fast virus
by Donatella Zorzetto
As the arrival of Omicron in November last year also demonstrated, in the case of Covid the speed of diffusion therefore seems to be the main factor determining the success of a viral variant.