“We observed isolated cases of delta diseases in late March and early April, after which delta was no longer detected, at least among the samples that were sequenced and uploaded to the VGARus database,” RIA Novosti quotes Khafizova.
After most people become immune to a particular strain, the conditions for that variant of the virus change and it becomes less "successful" to give way to other variants, he said.
The specialist stressed that "the delta strain, which has now virtually disappeared, may return if its reservoir is preserved somewhere, and the population will gradually lose immunity to this strain."
Earlier, immunologist Nikolai Kryuchkov, a public health and drug licensing expert, said that a subspecies of the omicron BA.2 strain that caused the outbreak in Shanghai had been circulating in Russia for a long time.