Early data indicate vaccines still protect against Omicron’s sister variant, BA.2

New data show that vaccines still protect against a spinoff of the Omicron variant, a welcome sign as the world keeps a close eye on the latest coronavirus iteration.

BA.2, as the sublineage is known, is part of the broader Omicron umbrella. Scientists are paying more attention to it as it begins to eat into the dominance of the more common Omicron strain, which is technically called BA.1.

BA.1 is what has driven massive spikes in cases around the world, but in countries including India, the Philippines, South Africa, and several countries in Europe, BA.2 has been picking up proportional steam and demonstrating a growth advantage over BA.1. The two lineages share many mutations, but have their own individual genetic twists as well.

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As with any emerging variant, there are more questions than answers about BA.2’s transmissibility, severity, and ability to erode the immunity built by vaccination or prior infection. As the World Health Organization put it last week, “drivers of transmission and other properties of BA.2 are under investigation but remain unclear to date.”

But data this week from the U.K. Health Security Agency — which has done some of the leading work on new variants — offered a piece of reassuring news: There does not seem to be any loss of vaccine effectiveness against BA.2 compared to BA.1.

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Vaccines already took a decent hit in the face of BA.1, particularly in their ability to prevent infection entirely, which is why so many immunized people have had breakthrough infections in recent weeks. But crucially, the vaccines’ protection against severe disease with Omicron has broadly stood up, and booster doses have helped shore up much of the protection that was lost.

This week, the U.K. agency estimated that, for people at least two weeks out from their booster shot, vaccine effectiveness against symptomatic disease was 63% against BA.1, versus 70% for BA.2. While that might suggest that BA.2 is less of a threat to vaccine protection than its Omicron sister, the full estimate ranges overlapped.

That helps answer one question about BA.2, but there remains another pressing one: what the spinoff’s snowballing means epidemiologically. The fact that it’s demonstrating a growth advantage in multiple countries suggests BA.2 might be able to outcompete BA.1 generally, though if that happens, it could be more of a slow ascendance than a lightning-quick grab of dominance. (When scientists in South Africa first identified what quickly became known as Omicron, they spelled out that there were already several lineages, including BA.2.)

Jacob Lemieux, an infectious diseases physician at Massachusetts General Hospital who is helping lead a state program studying variants, said that in some countries, BA.2 is displacing BA.1, but that, “what we don’t know, and still have almost no information on, is what impact this will have on case counts, on hospitalizations, on death.”

Variants can behave differently in different places, depending on the levels and types of immunity people have there and what else is spreading. Different variants can co-circulate. And the composition of infections can change — with an emerging strain coming to take the lead in a given place — even as the total number of cases declines or stays flat. Put another way, even if BA.2 becomes dominant, it doesn’t have to cause another spike.

One factor that will help determine that is cross-protection: essentially, how well are the millions of people who’ve now been infected with BA.1 protected against infection from BA.2? Some variants offer better cross-protection against other forms of the virus than others. It appears that people who’ve been vaccinated and infected with Omicron have strong protection against Delta, for example.

Another possibility is that BA.2 — if it is more transmissible in our current landscape than BA.1 — could cause another uptick in cases, but whatever spike occurs could be broadly limited to infections because of the high levels of population immunity. That is, the link between cases and subsequent hospitalizations and deaths could become even more decoupled than it already is.

This week, for example, Danish authorities announced that they were ending most pandemic restrictions starting next week, because even with a high infection tally, there were few resulting hospitalizations.

Source: STAT