A series of preliminary studies suggest that cellular immunity elicited by vaccines or prior COVID infections remains effective against the Omicron variant.

Why it matters: This form of immunity is associated with protection against severe disease. That means that while vaccinated people or those with prior infections are significantly less protected against Omicron infection, they're unlikely to become seriously ill.

Yes, but: It's still unclear how likely the Omicron variant is in the first place to cause serious disease, even in people who haven't been vaccinated or previously infected.

• Either way, this preliminary research — which has not yet been peer-reviewed — offers encouraging news for billions of people around the world, and is at least partially why Omicron isn't causing as high of hospitalization rates as other variants.

What they found: Multiple recent preprint studies, two of which were posted online yesterday, have found that T cell responses in vaccinated people or those with prior infections remain durable against Omicron.

• That's in contrast with their neutralizing antibody responses, which are generally associated with protection against infections and aren't as effective against Omicron.
• Vaccinated people who have received booster shots — or previously infected people who are also vaccinated — have greater levels of neutralizing antibodies, other initial studies have found.

Details: "Our data suggest that current vaccines may provide substantial protection against severe disease due to the SARS-CoV-2 Omicron variant despite reduced neutralizing antibody responses and increased breakthrough infections," one of the studies released yesterday concluded.

• A second study by Swedish researchers found that T cells induced by prior infection also remain effective against Omicron, but those induced by mRNA vaccines are even more protective.
• Other recent preliminary studies have reached similar conclusions.

The bottom line: There are multiple forms of immunity, and it appears that at least one of them — one that keeps people alive and out of the hospital — is holding up well against Omicron.