A sub-lineage of the ommicron coronavirus variant, called BA.2, continues to grow steadily around the world as scientists and health officials continue to work to understand the risk it poses to public health.
Until now, the general data has been a mix. Some recent laboratory and animal data have suggested that BA.2 may cause more serious disease than the original ommicron variant, BA.1. But so far, that finding doesn’t hold true in real-world data. Countries where BA.2 is dominant do not see higher rates of serious diseases. And in many places where BA.2 is increasing, cases are also decreasing along with hospitalizations.
While animal studies have suggested that BA.2 responds differently to some immune responses than the original omicron variant, so far real-world vaccine data finds two doses and booster doses to be just as effective — if not slightly more effective — against BA.2 than BA.1 .
However, everyone agrees on one thing: BA.2 is slightly more portable than BA.1, which was already considered ultra-portable. Studies have consistently shown that BA.2 has a growth advantage, and according to current estimates, the transfer of BA.2 is about 30 to 40 percent higher than that of BA.1. That explains how BA.2 is now crumbling BA.1’s global dominance.
BA.2 now accounts for at least 21 percent of all sequenced ommicron cases worldwide. It has overtaken BA.1 as the dominant virus in at least 10 countries, including Bangladesh, China, Denmark, India, Nepal, Pakistan and the Philippines. Where it rises, it rises quickly. In South Africa, for example, BA.2 rose from 27 percent on Feb. 4 to 86 percent on Feb. 11. In the United Kingdom, the prevalence of BA.2 increased sixfold between January 17 and January 31. has more than tripled from 1.2 percent in the week ending Jan. 29 to the most recent prevalence estimate of 3.9 percent on Feb. 12.
Usually good news
But those increases have not been accompanied by worrying increases in serious illness and hospitalizations, as noted in a recent World Health Organization epidemiological report. In Denmark, where BA.2 is rapidly approaching 100 percent of all infections, researchers have seen no difference in hospital admissions between people infected with BA.2 compared to BA.1. The analysis took into account gender, age, vaccination status, time period, region, comorbidity and prior SARS-CoV-2 infection. In South Africa, where BA.2 is also dominant, the number of hospital admissions continues to fall. And similarly, in Nepal, although BA.2 cases rose in February, cases continue to fall from late January, and the use of intensive care and mechanical ventilation is also declining.
All in all, those data are reassuring, given a recent pre-print study that suggests BA.2 appears to be more pathogenic than BA.1 — at least in lab and animal studies. The study, led by researchers at the University of Tokyo, found that BA.2 could bind better to human cells than BA.1 and replicate to higher levels in lung and nasal cells. In experiments with hamsters, the researchers also found that BA.2 caused a more serious lung disease than BA.1. Work with hamsters and mice also suggested that BA.2 could thwart immune responses generated on BA.1. But this finding did not hold up statistically when the researchers matched BA.2 with antibody samples from three unvaccinated people who had recovered from BA.1. The rodent data also conflicts with the real data from Denmark, referenced above.
Vaccination data from the UK and Denmark offer even more comfort. A recent UK Health Security Agency report found that current vaccines are just as effective, if not slightly more effective, against BA.2 than BA.1. Specifically, 25 weeks after a second dose, vaccines were 10 percent effective against symptomatic COVID-19 from BA.1 but were 18 percent effective against BA.2. Protection against symptomatic infection of BA.1 increased to 69 percent two weeks after a booster, but protection against BA.2 to 74 percent. Preliminary data from Denmark, mentioned in the WHO report, showed that vaccinated people with breakthrough BA.2 infections were less likely to spread the infection to household contacts than vaccinated people infected with BA.1
Overall, the WHO concluded that this “suggests that vaccination is at least as effective in preventing the acquisition of BA.2 and may be more effective in preventing the transmission of BA.2 compared to BA.1.”
