The World Health Organization said in a report Tuesday that the Delta variant was detected on 99.7% of diagnostic tests in the past 60 days.
The WHO said in a report that Delta was first identified in India in October 2020 and has now spread to 166 countries.
Delta's spread has been gradual in a few countries in South America. The report said that the Mu variant makes up a large proportion of the country's tests. In the past 60 days, the report found that each of those three variant accounted for less than 1% of the tests.
Not every country has access to sequencing facilities, WHO warned, and delays in uploading test results to the central database may mean some variant are undercounted.
The original coronaviruses has a number of descendants, according to Outbreak.info, which uses data from the Centers for Disease Control and Prevention. In the UK, where it has been detected most often, one descendant, AY. 4.2, is being closely monitored by public health bodies.
Dr. Soumya Swaminathan, chief scientist at WHO, said on Wednesday that AY 4.2 may have some transmission advantage and needs to be watched.
It's not clear if the spread of AY.4.2 is due to other factors in England or if it is due to innately more infectious. According to the most recent Public Health England report, the variant accounted for about 10% of Delta cases in England as of October 23 and 15% as of November 6.
The report found that the vaccines should protect against it.
