Covid-19 Variants Keep Getting More Contagious. Here's Why.

Since the start of the Covid-19 pandemic in 2020, the scientific understanding of its transmission and prevention has evolved. WSJ’s Daniela Hernandez explains what strategies have worked for stemming the spread of the virus and which are outdated in 2022. Illustration: Adele Morgan

As the Omicron subvariant BA.5 is the latest to take over and dash the hopes of a summer Covid-19 lull, researchers have attempted to quantify and explain its edge over earlier versions of the virus.

The BA.5 subvariant is estimated to be some 70% more transmissible than BA.2, which took over the landscape in the spring, said Trevor Bedford, a computational biologist at the Fred Hutchinson Cancer Center. That estimate is based on how quickly the BA.5 variant displaced its predecessor, he said.

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