Scientists say don't treat Omicron like a cold just yet — it could cause more havoc than Delta, even if symptoms appear 'mild'

Scientists say don't treat Omicron like a cold just yet — it could cause more havoc than Delta, even if symptoms appear 'mild'
Medical worker in London, UK wears personal protective equipment to protect against COVID-19 when doing tests on December 18.DANIEL LEAL/AFP/Getty Images
  • Experts have said we can't assess Omicron's severity from the early data we have.
  • Studies found fewer people were going to the hospital for Omicron than with Delta.

Scientists urged caution after four new studies suggested Omicron may result in milder COVID-19 illness than Delta, saying that the new variant shouldn't be dismissed as a coldlike infection just yet.

Studies from England, Scotland, Denmark, and South Africa estimated Omicron carried a 40 to 80% lower risk of hospitalization compared with the Delta variant.

These early studies indicated that COVID-19 illness caused by Omicron tended to be milder than Delta cases in relatively young populations with high levels of immunity, whether from vaccination or prior infection. But experts said that the data couldn't tell us whether the virus was inherently less deadly than Delta, while others said Omicron's transmissibility may pose the biggest threat. The studies haven't been peer-reviewed or published in medical journals.

"We're not in a place to treat this as a cold," Azra Ghani, a coauthor of an Imperial College London study on the subject, told The New York Times. The Imperial College London study estimated Omicron led to 40 to 45% fewer hospitalizations compared with Delta.

A key reason for the observed mildness of Omicron, experts said, is that it appears to be better than Delta at infecting people who have some level of protection.


Neil Ferguson, who led the Imperial College London study, said that the overall picture as the virus moved through the community month by month and eventually year by year "will be a milder one."

"It doesn't mean the virus necessarily is any fundamentally less virulent. It just means we have built up a lot more protection in the population," he told The Wall Street Journal.

Dr. Jim McMenamin, the national COVID-19 incident director at Public Health Scotland and a study coauthor, said in a press briefing Wednesday that the findings from Scotland — which found the risk of hospitalization was about two-thirds lower with Omicron than with Delta — was a "qualified good news story."

But McMenamin said that it was "important we don't get ahead of ourselves." For example, if it takes longer for people with Omicron to need hospital treatment than those with Delta, the results will be an "underestimate," researchers said in the briefing.

All the studies could take into account only known previous infections — Omicron could be causing "mild" illness in people who had been previously infected but hadn't shown symptoms or taken a test.


Unvaccinated people at 'especially high risk'

Whether or not Omicron causes a milder illness than Delta, the variant might cause more harm because of its fast spread.

Dr. Anthony Fauci, President Joe Biden's chief medical advisor, said in a briefing Wednesday that even with a diminution in severity, "if you have a much larger number of individual cases, the fact that you have so many more cases might actually obviate the effect of it being less severe."

James Naismith, a professor of structural biology at Oxford University, who wasn't involved in the studies, said in a statement to the Science Media Centre Wednesday that we should expect "different results as the science evolves."

Omicron can still cause severe illness in people who are fully vaccinated, he said. If Omicron case numbers continue to double every few days, that may generate many more hospitalizations than Delta in a fully vaccinated population, Naismith added.

William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, told The New York Times that the new findings showed unvaccinated people who hadn't yet caught COVID-19 were at "especially high risk."


"If you are unvaccinated, and you have never been infected, it is a little less severe than Delta," Hanage said about the findings, according to The Times. "But that's a bit like saying you're being hit over the head with one hammer instead of two hammers. And the hammers are more likely to hit you now."