Omicron subvariant BA.2 continues global rise as experts assess mixed data

The sub-lineage of the omicron coronaviruses variant, dubbed BA.2, continues to increase steadily around the globe as scientists and health officials are still working to understand the risk it poses to public health.

The data has been mixed so far. Recent laboratory and animal data shows that the original omicron variant, BA.1, can cause more severe disease than the newer variant, BA.2. That finding is not bearing out in real-world data. The countries that have BA.2 are not seeing higher rates of disease. Many places seeing BA.2 increasing are also seeing cases decline.

Real-world vaccine data shows that two doses and booster doses are just as effective against BA.2 as they are against the original omicron variant.

Everyone agrees that BA.2 is a little more transmissible than BA.1, which was already considered ultra transmissible. Studies have consistently found that BA.2 has a growth advantage, and current estimates peg BA.2's transmission as about 30 percent to 40 percent higher than BA.1's. That explains how BA.2 is chipping away at the domination of BA.

At least 21 percent of all omicron cases worldwide are accounted for by BA.2. In at least 10 countries, including Bangladesh, China, India, Nepal, Pakistan, and the Philippines, it is the dominant virus. It rises quickly where it rises. In South Africa, BA.2 went from 27 percent on February 4 to 86 percent on February 11. From January 17 to January 31, the prevalence of BA.2 in the United Kingdom jumped six-fold. In the US, it has more than tripled from 1.2 percent in the week ending January 29 to its most recent prevalence estimate of 3.9 percent as of February 12.

Mostly good news

The World Health Organization noted in a recent report that there have been rises in severe disease and hospitalizations. There has been no difference in hospitalizations among people with BA.2 compared with people with BA.1. Sex, age, vaccination status, time period, region, and previous infections were accounted for in the analysis. In South Africa, where BA.2 is also dominant, hospital admissions continue to decline. In Nepal, though BA.2 cases have risen in February, cases still continue to fall from late January, and use of intensive care and mechanical ventilation is on the decline.

A recent pre-print study suggests that BA.2 appears to be more dangerous than BA.1 in lab and animal experiments. The study found that BA.2 could bind to human cells better than BA.1 and could be replicated to higher levels in lung and nasal cells. The researchers found that BA.2 caused more lung disease than BA.1. Work with hamsters and mice suggested that BA.2 could affect immune responses. When the researchers compared the results from the three people who had recovered from BA.1 with the results from the three people who had not recovered from BA.1, the finding didn't hold up. The real-world data fromDenmark conflicts with the rodent data.

More comfort can be found in vaccine-effectiveness data from the UK. A recent report by the UK Health Security Agency found that current vaccines are just as effective as their predecessors. 25 weeks after a second dose, the vaccines were effective against COVID-19 from BA.1 but not against BA.2. Two weeks after a booster, the protection against BA.1 increased to 69 percent, but the protection against BA.2 increased to 74 percent. According to the WHO report, preliminary data fromDenmark shows that people with breakthrough BA.2 infections are less likely to spread the disease to household contacts than people with BA.

The WHO concluded that vaccination is at least equally effective in preventing acquisition of BA.2 and could be more effective in preventing transmission of BA.2.