Scientists are betting that the coronavirus omicron variant will be able to outsmart at least some of the protection people gained through either a previous COVID infection or vaccination. But even if that proves to be the case, the highly mutated variant won’t be able to totally evade our immunity.
Though omicron may wind up causing more mild breakthrough infections in vaccinated people and reinfections in people who previously had COVID, two vaccine doses still appear to provide strong protection against severe disease, hospitalization and death.
Early reports on omicron show that most cases in vaccinated people are surprisingly mild, suggesting that immunity is holding up very well. But what about boosters? And what happens if you only have two shots? Here’s everything to know so far:
How the shots hold up against omicron
Data on whether and how vaccine booster shots can protect generally healthy people from omicron, compared with the initial vaccine doses alone, is sparse. But very preliminary evidence suggests a third dose may restore waning antibody levels, so people’s chances of getting even a mild or asymptomatic infection are slim. However, for those less likely to mount a strong immune response after vaccination — people who are immunocompromised, elderly, or have multiple health conditions — a third dose can be lifesaving.
We’re in the very early stages of understanding how vaccines work against omicron, but preliminary evidence suggests that mild breakthroughs and reinfections may be more common with the variant. It also shows that two vaccine doses continue to provide strong protection against severe disease, and that a booster dose may help prevent most asymptomatic and mild infections.
A preliminary study released Tuesday suggests that antibodies — our first line of defense against the virus — aren’t quite as powerful at preventing omicron infections as they were with the ancestral coronavirus strain that hit in 2019, citing a 20- to 40-fold reduction in antibodies with two Pfizer doses. Another study determined there was only a 7-fold reduction in antibody levels against omicron. (Keep in mind these are studies conducted in a lab that offer some clues, but we need real-world evidence to truly know how the vaccines hold up against omicron.)
That might sound like a lot, but even though omicron has picked up new mutations, much of the virus looks the same. And we know antibodies can still interact with many different parts of the spike protein, explained Richard Martinello, a Yale Medicine infectious diseases specialist.
Furthermore, these lab studies looked at the impact on infection only — not severe illness. When it comes to preventing serious disease and severe outcomes like hospitalization and death, the immunity conferred by the initial vaccine doses seems to hold up very well in generally healthy people.
“We know that when people receive a booster, it greatly increases the amount of antibodies they have circulating in their blood, which are able to inactivate the virus.”
– Richard Martinello, Yale Medicine infectious diseases specialist
Scientists are looking into whether a booster shot adds protection against omicron infection, and we should have more data in the coming weeks. Pfizer released new study findings via a statement on Wednesday, saying three doses of the Pfizer shot increase antibodies 25-fold and successfully neutralize the omicron variant. That suggests a booster may help minimize healthy people’s chances of contracting even an asymptomatic or mild infection.
“We know that when people receive a booster, it greatly increases the amount of antibodies they have circulating in their blood, which are able to inactivate the virus,” Martinello said.
Having more antibodies that attack the unchanged parts of the spike protein is probably helpful when it comes to preventing mild disease, explained Monica Gandhi, an infectious disease specialist at the University of California San Francisco.
“Yes, I think a third dose will boost antibodies and likely protect against mild reinfection,” Gandhi said. “However, two doses are likely sufficient to protect against severe disease.”
How our immune system targets new COVID variants like omicron
This is not a reason to panic. In fact, infectious diseases experts say these early findings suggest that two doses of the vaccine are powerful enough to keep most people out of the hospital, even as the coronavirus picks up new mutations.
Remember, antibodies aren’t the only thing our immune system relies on to fight pathogens. The vaccines also stimulate our T cells and memory B cells, which are responsible for keeping an infection from worsening into severe disease. Even with all of omicron’s mutations, 80% of the epitopes, or targets, on the virus’s spike protein that T cells recognize and go after are unchanged.
In addition, when our B cells (which are primed from vaccination) see a new variant, they start producing a fresh batch of antibodies within a few days that specifically target the new variant.
“Your B cell-directed evolved antibodies come out and fight those mild symptoms,” Gandhi said.
And that’s just after two shots or hybrid immunity (vaccination plus previous infection). Evidence is currently mixed on how a third dose would impact T cells and B cells. Some studies claim a booster won’t have much of an effect on our immune memory, since it’s already so durable. Other reports suggest a booster will enhance it. Time will tell on that one.
But so far, it looks like this second line of defense — which, again, matters for preventing severe disease — may not be tricked by omicron. And while a booster is strongly recommended to prevent severe outcomes in at-risk individuals, healthy people might be able to avoid even the mildest infections with a third dose.
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.