Scientists at the Mirimus Laboratory prepare to test COVID-19 samples from recovered patients on April 8, 2020 in Brooklyn, New York.
Mischa Friedman | Getty Images
The rapidly spreading delta variant remains the “most worrying” strain of coronavirus despite the emergence of the mu variant, World Health Organization officials said Tuesday.
The mu variant, which was added to the WHO’s list of “interesting” variants last week, has mutations that suggest it could bypass immune protection through natural infections or vaccinations, Maria Van Kerkhove, the agency’s technical director for Covid-19, said during a virtual press event. Still, the new variant – first discovered in Colombia but now confirmed in at least 39 countries – is not as successful as the Delta, she said.
“The Delta variant is the one that is the most worrying for me because of the increased transmissibility,” Kerkhove said, adding that it has at least twice the transmissibility of the original ancestral virus that emerged in late 2019.
Delta has rapidly spread to at least 170 countries, including the United States, since it was first discovered in India in October, and has quickly become the predominant variety in many of those regions, according to the International Health Agency.
Mu, also known as B.1.621 by scientists, is increasing in some South American countries but is also decreasing in other regions of the world, especially where the delta variant is already in circulation, she said.
Any new virus that emerges has to be able to compete with the “best in class,” and that’s Delta right now, said Dr. Mike Ryan, WHO Director of Emergency Health Programs. The Delta variant tends to “crowd out” other variants like Mu, he said.
It doesn’t matter if a new variant has genetic changes that allow it to bypass vaccine protection if it can be transmitted efficiently, Ryan said.
“We’ll expect to see more” variants like Delta, he said. “Not every variant means the sky is falling. Each variant must be examined for its properties in terms of its potential to cause more serious diseases, its transmission potential and its potential to escape vaccines.”
The agency is monitoring four “worrying” variants: Alpha, which was first discovered in the UK; Beta, first discovered in South Africa; Gamma, first discovered in Brazil, and Delta. A variant of concern is generally defined as a mutated strain that is either more contagious, more lethal, or more resistant to current vaccines and treatments.
The WHO is also monitoring four other interesting variants – including lambda, which was first identified in Peru – that have caused outbreaks in several countries and that have genetic alterations that could make them more dangerous than other strains.
The Senior Medical Advisor to the White House, Dr. Anthony Fauci, raised concerns about the mu variant last week, saying it was not an immediate threat to the US
“We make sure we take everything so seriously, but we don’t see it as an immediate threat at the moment,” Fauci said at a press conference on Thursday.
The WHO has stated that further studies are needed to understand the clinical features of the new variant.
Right now it’s an “interesting line,” Ryan said on Tuesday. “When there is cause for concern, we really need to look into the diagnostics and development of our vaccines.”