Researchers from the University of Iowa and 14 other institutions discovered that the omicron variant of the coronavirus causes much less weight loss and lung disease in mice and hamsters, similar to preliminary data on its human effects.

The National Institutes of Health funded the project, offering the University of Iowa researchers about $110,000. The paper resulting from the research was published in the science journal Nature and explains that the omicron variant’s effects on weight loss and lung disease are minimal in mice and hamsters as compared to previous variants.

Stanley Perlman, a UI professor of microbiology and immunology and co-author on the paper, said ignorance about the severity of the omicron variant on humans sparked the researchers’ interest in the project. Perlman studied coronaviruses before the 2019 outbreak.

Scientists knew the now-dominant strain evades immune responses from vaccination and previous infection before the study, but not how potent it is, he said.

The many researchers involved studied different species of mice and hamsters to ensure no redundancy, he said.

“Hamsters and mice don’t get easily affected by the omicron variant unlike the other variants that we’ve seen, so we showed that in many different kinds of mice and many different kinds of hamsters,” he said. “What we can duplicate is the infection not being very severe, and that’s the only thing that’s in the paper.”

Perlman said the research is a starting place to understand why omicron appears to cause less severe disease than other variants.

“It was really to set up a system so that we could then study it and figure out why people have less severe disease, if in fact they do, there’s some controversy about that,” he said.

Lok-Yin Roy Wong, UI Perlman Laboratory postdoctoral research fellow and co-author on the paper, said that rodents given equal levels of COVID-19 infection suffered less weight loss and lung damage under omicron than previous strains.

It is not known for certain that omicron affects humans as weakly as rodents, despite what preliminary studies indicate, Wong said.

“I guess some studies show that people infected with omicron have lower rates of hospitalization, and they tend to do better compared to people infected with other variants,” he explained.

Abby Odle, Perlman Laboratory research assistant and co-author on the paper, also acknowledged scientists’ current ignorance about omicron’s detriment to humans.

“There’s a lot more factors to consider with humans as well, immunocompetency and stuff like that,” Odle said. “We’re just using competent mice, but there’s many more factors that come into play when you’re talking about humans, so they can’t be directly compared but it gives you a pretty good indicator.”

Odle said they will soon be studying whether the infection of mice by previous COVID-19 strains builds their immunity against omicron.