Coronaviruses are single-stranded RNA viruses with large genomes and, until recently, consisted of the mild 229E, OC43, L69, and H53U1 strains, and the "novel" SARS and MERS strains. Sometime in late 2019, a third "novel" coronavirus called the "Wuhan" strain emerged. This began what we now know as the COVID-19 pandemic. With subsequent mutation, "variants of concern" soon emerged, starting with Alpha, and the most significant subsequently being Delta and then Omicron. [ MedPage Today 6.7.2022]

Mutations evolved and new strains replaced older variants. Now we are in the Omicron subvariant replacement phase. BA.1 was replaced by BA.2 and then BA.2 was replaced by BA.2.12.1. Starting in early 2022, the latest of these subvariants of concern became the BA.4 and BA.5 subvariants, originally described in South Africa. The earliest samples of BA.4 and BA.5 in the U.S. were collected on March 30 and March 29, respectively. 

Each time a new variant comes along, it feels like we're starting from scratch all over again. How fast is the new variant spreading? What does the symptomatology and severity look like? While many questions remain about these new subvariants, below I review current insights into their transmissibility, disease severity, and survivability.

What We Know

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