Economist forecasts omicron’s infectiousness

Remember alpha, the first COVID-19 variant? Alpha put the world on alert that mutations can change everything we thought we knew — within mere weeks — about what to expect from COVID-19.

Back then, economist Peter Reinhard Hansen was skeptical of reports that alpha was 50% more infectious than the original coronavirus, SARS-CoV-2.

“I was surprised and wondered if the high number could be true,” said Hansen, the Henry A. Latané Distinguished Professor of Economics.

So Hansen began crunching the numbers himself.

Building on statistical methods from econometrics — which he typically applies to models of financial volatility — he built a model, outlined in the Econometrics Journal, to estimate the infectiousness of new viral variants and better predict case numbers once a new variant emerges.

Hansen used health data available from Denmark to calculate a value known as the reproductive number (R₀) for alpha. This value characterizes the average transmissibility of an infectious disease in a susceptible population with little to no immunity. (Back when alpha was spreading, vaccines were not yet widely available in Denmark.)

“Everything I had read in the early reports turned out to be true,” Hansen said.

After incorporating up-to-date health data, Hansen’s model showed that the delta variant was about two times more infectious than alpha, and that omicron was about three times more infectious than delta in the Danish population.

Forecasting the infectiousness of viral variants is crucial to developing public health mitigation strategies, and for allocating resources in health care settings, Hansen said.