Early evidence that boosters seem to hold up against Omicron subvariant BA.2

With BA.2 now spreading in more than 50 countries around the world, there's early hope that vaccine booster doses still hold up against the Omicron subvariant.

An initial analysis of vaccine effectiveness by scientists in the U.K. — where the subvariant is expected to become dominant in the next month — found a similar level of protection against both siblings in the Omicron evolutionary family tree: BA.1, which is still dominant globally, and BA.2, which is rising in multiple countries.

In the findings released on Thursday, which combined results from all COVID-19 vaccines being used in the U.K., the effectiveness in warding off symptomatic infection after two doses was nine per cent against BA.1 and 13 per cent against BA.2, after 25 or more weeks post-vaccination.

The level of protection jumped to 63 per cent against BA.1 and 70 per cent against BA.2 two weeks following a booster shot, the analysis continued.

That hopeful early finding comes as BA.2 cases are ticking up in Canada, with early federal data showing a slight rise in recent weeks.

In a Public Health Agency of Canada briefing on Friday, Dr. Theresa Tam said the country's overall Omicron wave appears to be peaking.

At the same time, more than 100 cases of BA.2 have been detected in Canada since November, with about 77 of those identifications coming from the National Microbiology Laboratory, plus further reporting from provinces and territories, she said.

There's "always a possibility" that this wave could wind up extended, Tam said.

South of the border, data also shows that BA.2 is being reported in 24 U.S. states, and in Denmark, it's displacing BA.1, all while the country is lifting its last restrictions.

Danish scientists recently reported, reassuringly, that there's no difference in hospitalizations when compared with BA.1, and vaccines are expected to continue offering protection against severe illness — though early data does show that BA.2 may be more than 1.5 times more transmissible.

That early signal echoes the properties of the original Omicron strain, which is highly contagious yet often leads to less severe disease than the Delta variant, in part thanks to global vaccination efforts.

Even so, the variant is still putting significant pressure on many health-care systems due to the sheer number of cases, including in Canada, prompting the cancellation of scheduled surgeries in multiple provinces.

The U.K. Health Security Agency (UKHSA) agreed on Friday that data shows BA.2 appears to have a substantial growth advantage over its predecessor.

"We now know that BA.2 has an increased growth rate, which can be seen in all regions in England," said Dr. Susan Hopkins, chief medical advisor for the UKHSA, according to a Reuters report.