The omicron subvariant known as BA.5 was first detected in South Africa in February 2022 and spread rapidly throughout the world. As of the second week of July 2022, BA.5 constituted nearly 80% of COVID-19 variants in the United States.

Soon after researchers in South Africa reported the original version of the omicron variant (B.1.1.529) on Nov. 24, 2021, many scientists – including me – speculated that if omicron’s numerous mutations made it either more transmissible or better at immune evasion than the preceding delta variant, omicron could become the dominant variant around the world.

The omicron variant did indeed become dominant early in 2022, and several sublineages, or subvariants, of omicron have since emerged: BA.1, BA.2, BA.4 and BA.5, among others. With the continued appearance of such highly transmissible variants, it is evident that SARS-CoV-2, the virus that causes COVID-19, is effectively using classic techniques that viruses use to escape the immune system. These escape strategies range from changing the shape of key proteins recognized by your immune system’s protective antibodies to camouflaging its genetic material to fool human cells into considering it a part of themselves instead of an invader to attack.

I am a virologist who studies emerging viruses and viruses that jumped from animals to humans, such as SARS-CoV-2. My research group has been tracking the transmission and evolution of SARS-CoV-2, evaluating changes in how well the omicron subvariants evade the immune system and the severity of disease they cause after infection.

How is virus transmissibility in a population measured?

The basic reproduction number, R0 – pronounced “R-naught” – measures the transmissibility of a virus in a yet-uninfected population.

Once a proportion of individuals in a population become immune due to prior infection or vaccination, epidemiologists use the term effective reproduction number, called Re or Rt, to measure the transmissibility of the virus. The Re of the omicron variant has been estimated to be 2.5 times higher than the delta variant. This increased transmissibility most likely helped omicron out-compete delta to become the dominant variant.

Read more: https://theconversation.com/how-the-omicron-subvariant-ba-5-became-a-master-of-disguise-and-what-it-means-for-the-current-covid-19-surge-187132