At this point, a whole lot of people have already experienced Omicron. Now BA.2, an extra contagious sub-variant of Omicron, is swiftly traveling the globe.
BA.2 has already taken over in both Europe and the northeastern US, exerting dominance over other versions of the Omicron variant (including BA.1, BA.1.1 and B.1.1.529.)
Researchers estimate that around 40% of the US has been infected with Omicron so far. Over in England, the government is reporting that about 1 in 20 people have COVID right now, and almost all of those cases (99.7%) are some form of Omicron.
As pandemic restrictions have been lifted across Europe this spring, there's been a noticeable spike in infections with BA.2 across that continent.
Because Covid-19 infections are on an uptick right now, many who've been infected in recent months are wondering: could I get Omicron again?
The short answer is: probably not.
Here's what we know so far:
Reinfection with Omicron is possible, but not common
Researchers in Denmark, where scientists sequence lots more Covid-19 cases that in other spots around the globe, have found that reinfection with BA.2 after BA.1 can happen, but it's quite rare.
Looking at data from more than 1.8 million cases in the three month period between November 2021 and February 2022, they found just 47 reinfections of BA.2 after BA.1. Most of those were in "young, unvaccinated individuals," the researchers wrote. A similar story has played out in England, where among more than 500,000 sequenced BA.1 and BA.2 specimens taken between November and late February, just 43 potential reinfections* were discovered (*the data is still preliminary.)
It's worth caveating those reassuring statistics, however, by noting that the studies were done in a very short period of time. It's unclear how long Omicron immunity may last, and how well it actually works for everyone.
Some lab studies done with blood samples found BA.1 infections provide decent cross-protection against BA.2
Again, not a ton of data, but a letter posted in the New England Journal of Medicine on March 16 evaluated blood samples from 24 vaccinated and boosted individuals who'd never had Covid before, and eight people who'd been infected recently, so presumably contracted BA.1 (all of them were vaccinated but one).
That study suggested that:
- The people most vulnerable to BA.2 are the unvaccinated who were not infected with BA.1
- Booster shots appeared quite helpful to prop up antibody levels against both BA.1 and BA.2 for people who had never been infected
- The people with the best protection against BA.2 were people who were vaccinated, boosted, and previously infected
- On average, vaccinated people in the study who had a prior Covid-19 infection (presumably BA.1) had more than three times the level of neutralizing antibodies against BA.2 as anyone else did.
That suggests there's "a substantial degree of cross-reactive natural immunity" for BA.2 from BA.1, the researchers said.
Booster shots will likely work as well on BA.2 as they did on other versions of Omicron
The same New England Journal of Medicine letter mentioned above showed that booster shots work almost as well against BA.2 as BA.1.
We have lots of data from the Omicron outbreak that peaked in January in the US which also suggests that boosted individuals, even those without a prior infection, fare very well against bad outcomes with Omicron.
The only lingering question is how fast that booster shot protection might be fading now that more time has elapsed since people got their third shots (or, second shots for those who had Johnson & Johnson).
"Hybrid" immunity shows there are advantages to vaccinating or boosting people who've had Covid
A much larger preprint study, which relied on vaccination and infection data from the entire country of Qatar, was posted online Tuesday. It hasn't been peer-reviewed yet, but like the NEJM letter, it suggests that the very best protection against an Omicron infection, whether with BA.1 or with BA.2, is a prior infection plus a recent booster shot.
The study found that from late December to late February in Qatar:
- prior infection with Covid reduced the risk of infection with BA.2 by 46%
- vaccination plus a recent booster reduced the risk of infection by 52%
- so-called "hybrid" immunity (2-dose vaccination + prior infection) reduced the risk of infection by 55%
- "hybrid" immunity plus a recent booster reduced the risk of infection by 77%
- two-dose Pfizer vaccination without a recent booster shot had a "negligible" effect on preventing Omicron infections, though those fully vaccinated patients were still well-shielded from severe disease, hospitalisation, and death during the Omicron wave. (Pfizer's is the most commonly-used Covid vaccine in Qatar.)
The bottom line
The emergence of BA.2 isn't to be dismissed as nothing to worry about, particularly because there are plenty of vulnerable people who may not have caught BA.1, and who could suffer a dangerous outcome with the more infectious BA.2.
However, there is some emerging data that suggests that, at least for a little while, a prior Omicron infection may provide some decent immunity against BA.2 Omicron.