A subline of the Omicron variant coronavirus, designated BA.2, is growing steadily around the world as scientists and public health officials are still working to understand the risk it poses to public health.
So far, the overall data has been mixed. Some recent laboratory and animal data suggest that BA.2 can cause more severe disease than the original omicron variant BA.1. But so far this finding has not been confirmed in real data. Countries where BA.2 is dominant do not see higher rates of serious illness. And in many places where BA.2 is increasing, cases are also declining, along with hospitalizations.
While animal studies suggest that BA.2 interacts with some immune responses differently than the original Omicron variant, real-world vaccine data to date shows that two doses and booster doses are 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 found BA.2 to have a growth advantage, and current estimates suggest that Peg BA.2 transmission is approximately 30 to 40 percent higher than BA.1. This explains how BA.2 is now crushing BA.1’s global dominance.
BA.2 now accounts for at least 21 percent of all sequenced omicron 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 fast. In South Africa, for example, BA.2 rose from 27 percent on February 4 to 86 percent on February 11. In the UK, BA.2 prevalence increased six-fold from 17 January to 31 January. And even in the US, it has more than tripled from 1.2 percent in the week ended January 29 to its most recent prevalence estimate of 3.9 percent on February 12.
Mostly good news
But these increases have not been accompanied by worrisome increases in serious illness and hospitalizations, as noted in a recent epidemiological report from the World Health Organization. In Denmark, where BA.2 is fast approaching 100 percent of all infections, researchers have seen no difference in hospital stays among people infected with BA.2 compared to BA.1. The analysis took into account gender, age, vaccination status, period, region, comorbidity and previous SARS-CoV-2 infection. In South Africa, where BA.2 also dominates, hospital admissions continue to decline. And in Nepal too, although BA.2 cases rose in February, cases continue to decline from late January, and use of critical care and mechanical ventilation is also declining.
Taken together, these data are reassuring a current preprint Study suggesting that BA.2 appears to be more pathogenic than BA.1 – at least in laboratory and animal studies. The study, led by researchers from the University of Tokyo, found that BA.2 can bind to human cells better than BA.1 and can be replicated at higher concentrations in lung and nasal cells. In experiments with hamsters, the researchers also found that BA.2 caused more severe lung disease than BA.1. Work in hamsters and mice also suggested that BA.2 might thwart the immune responses generated on BA.1. But that finding didn’t hold up statistically when the researchers compared BA.2 to antibody samples from three unvaccinated people who had recovered from BA.1. The rodent data are also in conflict with the above real data from Denmark.
Vaccine efficacy data from the UK and Denmark offers even more comfort. A recent report from the UK Health Security Agency found that current vaccines against BA.2 are just as effective – if not slightly more effective – than BA.1. Specifically, 25 weeks after a second dose, the vaccines were 10 percent effective against symptomatic COVID-19 from BA.1 but 18 percent effective against BA.2. Protection against symptomatic infection by BA.1 increased to 69 percent two weeks after a booster dose, but protection against BA.2 increased to 74 percent. Preliminary data from Denmark, mentioned in the WHO report, found that vaccinated individuals with breakthrough BA.2 infections were less likely to transmit the infection to household contacts than vaccinated individuals infected with BA.1
Overall, the WHO concluded that this “suggests that vaccination is at least as effective in preventing acquisition of BA.2 and may be more effective in preventing transmission of BA.2 compared to BA.1”.
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