Omicron variant’s ‘milder’ severity is likely due to more population immunity: Harvard researchers

While some have said the omicron variant is a less severe strain, Harvard researchers have found that the variant’s “milder” outcomes are likely due to more population immunity compared to earlier waves of the COVID-19 pandemic.

Because omicron infections are not necessarily intrinsically milder, those who are not yet protected should be the focus of renewed vaccination and boosting efforts, the researchers emphasize.

After the variant quickly spread throughout South Africa in late November, omicron resulted in lower hospitalization and death rates. That caused some to conclude that the variant causes less severe outcomes — or is less virulent.

But the Harvard researchers in their analysis argue that the perceived lower severity of omicron is most likely due to the level of immunity in infected people.

“There must be a renewed push to vaccinate and boost those not yet protected, because omicron is not necessarily intrinsically milder,” said William Hanage, associate professor of epidemiology at Harvard T.H. Chan School of Public Health.

“This is especially true for those struggling to access vaccines, whether in the United States or elsewhere in the world,” he added.

Hanage worked on the analysis with Roby Bhattacharyya, assistant professor at Massachusetts General Hospital and Harvard Medical School.

By the fall of 2021, much of the South African population had been vaccinated or probably infected by another variant during earlier waves. This previous exposure would likely have reduced the severity of a subsequent omicron infection, the researchers said.

The milder symptoms may also be due in part to omicron’s ability to cause breakthrough infections and reinfections, including in people who have stronger immune systems and are better equipped to fight off an infection, according to the researchers.

They caution that the situation in South Africa is different than that of other countries — especially the young age of its population — meaning that omicron could progress differently around the world.