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On the heels of concerning new lab and animal experiments suggesting that BA.2 may be capable of causing more severe disease than the original Omicron strain, two new studies are helping to show how well human immunity is defending against this strain in the real world.
Even as COVID-19 cases have been dropping around the world, the relative proportion of cases caused by BA.2 has been increasing.
“As of now, I don’t think that we need to sound a global alarm. But I do think that we need to pay attention to BA.2 because it does appear to have a growth advantage over BA.1,” said Dr Dan Barouch, director of the Centre for Virology and Vaccine Research at Beth Israel Deaconess Medical Centre in Boston.
Now new studies are providing some reassurance that while BA.2 may overtake its genetically distant cousin, it won’t likely lead to greater numbers of hospitalisations and deaths.
“The situation that we’re seeing on the ground, and I get this from talking to a number of my colleagues who actually do the genomic surveillance, is BA.2 is kind of creeping up in terms of numbers, but it’s not the meteoric rise that we saw with BA.1,” said Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organisation at the University of Saskatchewan in Canada.
That’s because in many countries like the US, UK and Denmark, BA.2 has hit speed bumps left in its wake by BA.1, which was already very contagious.
“It’s so soon after that initial BA.1 peak that you have a lot of people who were either vaccinated or boosted [or] got Omicron, and so right now all of those people will have relatively high titers of antibodies, neutralising antibodies that will protect against infection,” Dr Rasmussen said.
The new studies are preprints, which means they were posted to an online library of medical research before being reviewed by outside experts and published in medical journals.
No increase in hospitalisations
Researchers looked at cases tied to more than 95,000 positive COVID-19 tests. Among these, roughly equal proportions of people were hospitalised for their infections – roughly 3.6 per cent of people who had presumed BA.2 infections compared to 3.4 per cent of those with signs infections caused by BA.1.
After researchers accounted for things that might influence a person’s risk of severe disease, such as older age, they found no difference in the risk for hospitalisation between people infected by BA.1 and those infected by BA.2.
Roughly one-quarter of people hospitalised with both BA.1 and BA.2 infections were fully vaccinated.
Those findings echo hospitalisation studies from Denmark, where BA.2 is also the predominant cause of COVID-19 infections.
The lead researcher on the South African study, Dr Nicole Wolter, said that while it’s difficult to say how the South African experience with this variant may translate to other countries, what they’re seeing from BA.2 after their fourth wave isn’t a second peak, but a longer tail.
“We have seen an extended wave which has currently plateaued at a higher level than we have seen in previous inter-wave periods,” Dr Wolter wrote in an email to CNN.
“This may however also be influenced by schools opening following the December holiday period and a general relaxing of restrictions.”
Though cases have stayed at a high level, and most are now caused by BA.2, hospitalisations have continued to decline.
What about reinfection risk?
The study found that people who’ve recently had a COVID-19 infection caused by Omicron or Delta can be re-infected by the emerging BA.2 subvariant, but such cases appear to be uncommon, afflict mostly those who are unvaccinated and result in mostly mild infections.
BA.2 is currently the dominant cause of COVID-19 in Denmark. It overtook BA.1 during the second week of January there.
To look at reinfection risk, researchers combed through more than 140,000 viral genomes that were sequenced from infections during the period when Omicron became dominant (late November to mid-February 2022) to find people who had a new positive test 20 to 60 days after a previous one.
They found a total of 263 reinfections, with 190 of those caused by the BA.2 variant. In 140 cases, the person was re-infected by BA.2 after an infection caused by the Delta variant.
There were 47 cases where people were first infected by BA.1 (the original Omicron variant) followed by the BA.2 subvariant.
Researchers then did a more in-depth analysis of those 47 reinfections where BA.2 followed BA.1. Most of the individuals who were re-infected were young — 30 were under age 20.
None of the re-infected individuals was over age 40 and nearly all — 42 of the 47 individuals — were unvaccinated.
For the most part, reinfections were mild; 28 people had no symptoms or mild symptoms. Five people experienced symptoms that were characterised as moderate, akin to flu-like symptoms.
There were no hospitalisations or deaths reported among re-infected individuals.
The study shows that “reinfection can happen with people who recently recovered from BA;1, but it’s pretty rare. And in all those cases, it wasn’t severe,” says Dr Rasmussen, who reviewed the study but was not involved in the research.
What that means she says is that while BA.2 reinfection is a risk, it is a small risk relative to the entire population, and “that recent immune boost caused by either boosters, or recent Omicron infection is largely going to protect most of the population against it,” she said.
Source: 9News
