Forecasts of SARS-CoV-2 variant scenarios reveal what turns the virus could take

Looking ahead to June, researchers released forecasts in a preprint for hospitalizations and death tolls of five different SARS-CoV-2 variant scenarios eyeing what might be next and how to prepare accordingly.

To properly forecast the most likely and least likely possible variant scenarios, researchers looked at "vaccine uptake and effectiveness, antiviral administration, the emergence of new variants, and waning protection from both infection- and vaccine-derived immunity," the authors wrote. Using that information, they looked at the levels of hospitalizations, location and related information for past variants to inform what could emerge should anything change in the coming months.

On a baseline level, if nothing changes from now to June, they estimate there will be 3.54 billion infections, 6.26 million hospitalizations and 1.58 million deaths worldwide. If any change does occur, the most likely thing to happen will be a shift in an omicron-like variant, which could lead to 5.19 billion infections, 13.6 million hospitalizations and 2.74 million deaths. 

The least likely scenario is the emergence of a variant that combines the infectiousness of omicron with the severity of delta, which if it did occur, could result in 5.19 billion new infections, 30.2 million hospitalizations and 15.9 million deaths, according to the forecasts.

Why and how new variants emerge across the world and how far they evolve and spread is a complex question. A lot of it is based on ancestral variants and which new one can evolve to infect more in different populations, according to Bobby Reiner, PhD, an associate professor of health metrics sciences at the University of Washington in Seattle and one of the lead researchers on the forecasting. 

"For omicron, it was just so much more infectious than delta," he told Becker's. "So it was able to be more successful as a new variant and take over. Additionally, another thing we've been including in our models this whole time, is global travel, which started back up again quite a bit a couple of months before omicron emerged, so that also allowed it to get around the world really quickly."  

He explained that as omicron has risen to be the most common variant in the U.S. and in several places around the world, even though delta was also getting around globally, the infectious rate of omicron out weighed it. Other variants, like alpha, beta and gamma, did not spread nearly as widely around the globe. Dr. Reiner said this is "partially because of travel and partially because of where they showed up provisionally, but unfortunately, a bit of it is just luck."

"Omicron really hastened the end of the pandemic phase. I think some people don't realize how much closer to herd immunity omicron took us," he said. "In no way am I saying that it is not serious. It is still something that's killing people or severe, but compared to delta, it has been milder, at least in the U.S." 

In addition to the forecasts, the team also projected which interventions could be most effective at saving lives for each scenario. What they found indicates that globally increased mask usage "could prevent up to 28 percent of the projected deaths," and that "a moderate level of mandates similar to those that were instituted in 2021 and not the severe lockdowns of 2020 would prevent up to 36 percent of the projected deaths."


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