What Are The Differences Between The Omicron And Delta COVID Variants?

Experts explain how the two strains compare when it comes to immunity, vaccines, mutations, breakthrough cases and more.

Though all eyes are on omicron right now, the bulk of coronavirus cases in the United States are still from the delta variant.

But given omicron’s speedy spread in South Africa, epidemiologists strongly suspect it will soon outcompete delta in many other regions across the globe. Just take a look at how rapidly omicron is ripping through the Netherlands.

While we’re still in the very early stages of understanding how omicron compares to delta, preliminary evidence suggests the new COVID-19 variant may be more contagious but less severe than its predecessor. But there are too many other contributing factors — like how much immunity a population already has, along with seasonality and behaviors — to know if that is definitively the case.

Even with all that uncertainty, epidemiologists have a few early guesses at how omicron and delta may differ. Here’s what we know so far:

Omicron has more mutations than delta.

For the delta variant, the part of the spike protein that attaches to our cells is very similar to what existing coronavirus vaccines are designed to go after. But in the case of the omicron variant, the spike picked up 32 mutations that make it more difficult (though not impossible) for our immune system to recognize and prevent the virus from causing an infection.

“The omicron spike is still 97% identical to the vaccine, but the changes are clustered in a way that makes it harder for the immune system to neutralize,” said Benjamin Neuman, chief virologist at Texas A&M University’s Global Health Research Complex. According to Neuman, all of the mutations in omicron have been seen before in other variants — but they have never been clustered together exactly as they are in omicron.

While the vaccines may take a slight hit in efficacy, Neuman expects that antiviral drugs — remdesivir, molnupiravir and Paxlovid, the coronavirus pill — will remain just as effective against omicron as they were against delta and previous variants because they target parts of the virus that remain unchanged.

Though there’s so much uncertainty about omicron, epidemiologists seem convinced the new variant will outcompete delta across the globe.

“Omicron will displace delta as the dominant variant, just as delta replaced alpha. I think that’s pretty certain,” said Andrew Noymer, a University of California, Irvine epidemiologist and demographer who studies infectious diseases.

Experts have a few theories about how omicron differs from delta, but more data needs to be collected.
FotografiaBasica via Getty Images
Experts have a few theories about how omicron differs from delta, but more data needs to be collected.

Reinfections and breakthrough infections may be more common with omicron.

South Africa has seen more reinfections and breakthrough infections with omicron than with delta. Early predictions estimate that omicron is twice as infectious as delta, and a briefing from the United Kingdom shows a possible three- to eight-fold increase in reinfection from the omicron variant compared to other variants like delta and beta.

I have no doubt omicron is more transmissible than delta,” Noymer said.

A large report from South Africa’s largest health insurers looked at 78,000 omicron patients and estimated that the protection against hospitalization from two doses of the Pfizer coronavirus vaccine fell from 93% with delta to 70% with omicron. This could be due to waning antibody levels, or to the mutations on omicron outsmarting some of our antibodies.

Another new lab study found that omicron may replicate about 70 times faster than the delta variant, but that, unlike delta, it does so in the bronchi — the airways leading into the lungs — rather than in the lungs themselves.

These findings are not definitive, but they may explain why omicron might be more transmissible, yet less severe than delta.

“I have no doubt omicron is more transmissible than delta.”

- Andrew Noymer, University of California, Irvine

The good news is that we have a way to restore optimal protection against the omicron variant — booster shots. While it’s widely believed that two doses of the Moderna or Pfizer vaccines still provide strong protection against severe outcomes like hospitalization and death, growing evidence suggests a third dose of either vaccine can successfully neutralize omicron, similarly to delta, and prevent the variant from forming an infection.

Omicron symptoms may be milder than delta symptoms.

Even though omicron cases are growing rapidly, reports on hospitalization rates suggest omicron infections are milder than delta infections. After adjusting for vaccination status, data shows COVID hospitalizations in South Africa are 29% lower compared to what they were in mid-2020. People with mild omicron infections tend to bounce back faster, too, often recovering within three days.

Infectious diseases experts suspect omicron may not inherently be a milder variant, but may simply be causing milder illness due to all the preexisting immunity in the population, from both previous infections and vaccinations. According to Noymer, omicron looks less severe, but that’s in populations that have already been ravaged by delta (which is, more or less, everywhere).

The big question now: Is omicron actually less severe, or did delta leave so much immunity in its wake that it carved out a milder path for omicron?

Delta was a disaster from the get-go, said Monica Gandhi, an infectious disease specialist with the University of California, San Francisco. It came in like a firestorm, and the hospitalization rate in hard-hit places like India immediately surged. We’re not seeing that with omicron.

“To me, there is something different about this variant,” Gandhi said.

Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.

Popular in the Community


HuffPost Shopping’s Best Finds