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Faye Flam

The Omicron BA.5 Wave Is Starting to Ebb. We Need to Know Why.

Scientists are starting to figure out why infection rates rise and fall. But a collapse in Covid testing will make it much harder to predict the next surge.

Waves come and go.

Waves come and go.

Photographer: Joseph Prezioso/AFP/Getty Images

The Covid wave fueled by the omicron BA.5 surge is finally starting to ebb in the UK and in some of the harder-hit parts of the US. But why? It’s no longer tenable to argue that disease waves peak and fall primarily because people start taking precautions. People, especially in these two countries, are taking fewer precautions all the time. 

Scientists are starting to get a handle on the complex factors that drive waves up and down. Behavior patterns are just one small factor. Changing seasons, new contact patterns and waning immunity can drive waves up, and growing immunity can drive them back down.