Early Data Doesn't Back Hope That Omicron Will Be Milder

UK researchers say they see no indication that omicron will be milder than the delta variant of the coronavirus. In fact, they found the new strain's reinfection rate to be more than five times as high as delta's, Reuters reports. The Imperial College London study, which has not been peer reviewed yet, used government data on people who tested positive in England from Nov. 29 to Dec. 11. And a past infection might provide protection from reinfection as low as 19%, the college said. While noting that there's little data on hospitalizations so far to work with, the study's authors wrote, "We find no evidence of Omicron having different severity from Delta."

Compared to delta, omicron brings a substantially higher risk of a symptomatic illness, the researchers said, for anyone at least two weeks past their last vaccine dose or booster shot. AstraZeneca and Pfizer vaccines were used in the study. "This level of immune evasion means that omicron poses a major, imminent threat to public health," the lead professor said. A former chair of the UK Vaccine Taskforce cautioned about the findings, though, saying they're based on assumptions when adequate data are lacking. "For example, we have no data on the cellular immune response, which is now probably driving effectiveness of vaccines," Dr. Clive Dix said.

Despite signs in South Africa that fewer people infected with omicron are being hospitalized than those with delta, experts are cautioning about that data, too. The new variant could act differently in the US than it does there, per NPR. For one thing, vaccination rates in South Africa are so low—around 25%—that most people probably had already been infected with another strain. "Thus, omicron enters a South African population with considerably more immunity than any prior SARS-CoV-2 variant," two experts wrote in a study posted online this week. It's tough to measure vulnerability in the US, but one estimate is that 66 million people have not been infected and have not been vaccinated. (More omicron variant stories.)