Transmissibility, severity, reinfection of the Omicron BA.2 subvariant

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A more contagious sub-variant of omicron, known as BA.2, is spreading across the world and may soon become the dominant version of Covid-19.

It is now the main variant in at least 18 countries and is spreading rapidly, accounting for 35% of all new cases that have been genetically sequenced globally, up from ten countries and 21% of cases the previous week, according to new data. of the World Health Organization. In the United States, BA.2 currently accounts for 3.8% of genetically sequenced Covid cases, according to the Centers for Disease Control and Prevention.

A pandemic-weary public wants to know two main things: Will BA.2 cause a second wave of omicron cases, and put even more people in hospital with serious infections? So far, scientists say the answer to both questions is probably no.

However, Danish scientists confirmed this week that the new subvariant can re-infect people who have had omicron before, although it doesn’t seem that common. They also agree that it is more contagious than the original omicron version, BA.1, which is still widely circulating around the world.

But surprisingly, this does not cause a second wave of omicron infections. Globally, Covid cases have plunged 21% over the past week – falling in all regions except the Western Pacific – while deaths have fallen 8% over the past week, according to the WHO data.

Maria Van Kerkhove, the WHO’s technical lead for Covid-19, said the world health agency was closely monitoring countries that had detected BA.2, but so far the subvariant has not. did not cause a further increase in cases.

“While we see this drop in cases in countries, we no longer see an increase with BA.2,” Van Kerkhove said during a question-and-answer session broadcast live on social media platforms. WHO on Tuesday.

Here’s what’s known about the sub-variant so far.

More transmissible

Danish researchers have found that BA.2 is about 30% more transmissible than BA.1. Denmark was one of the first countries where BA.2 became dominant, and public health authorities around the world have been paying close attention to the situation there to better understand what the subvariant might mean for the future course of the pandemic.

“We conclude that Omicron BA.2 is inherently much more transmissible than BA.1,” said a team of scientists affiliated with Danish public health authorities and the University of Copenhagen. written in a study last monthwhich has not yet been peer reviewed.

The UK Health Security Agency found at the end of January that BA.2 had a substantial advantage over BA.1 in England. “We now know that BA.2 has an increased growth rate which can be seen in all parts of England,” said Dr Susan Hopkins, the agency’s chief medical adviser.

“If what is reported is true that BA.2 is slightly more transmissible, then my strong bias is to say that BA.2 will probably take over wherever BA.1 was,” said Mehul Suthar, a virologist at the University. Emory.

However, Suthar said that doesn’t necessarily mean BA.2 will cause a wave of infection. BA.2’s ability to cause another wave depends, in part, on its ability to re-infect people who have already caught and recovered from omicron, Suthar said.

Possible reinfection, but seems rare

Danish scientists confirmed on Tuesday that the BA.2 subvariant can re-infect people who previously had its omicron predecessor, BA.1, although the risk of catching the virus again appears low.

The Staten Serum Institute in Copenhagen analyzed a randomly selected sample of 263 reinfection cases. Forty-seven people caught BA.2 less than two months after infection with BA.1, according to the study. The majority of people reinfected with BA.2 after BA.1 were under 20 years old and unvaccinated.

“The rate of reinfection appears to be low given the high number of positive tests for SARS-CoV-2 during the study period, but still underscores the need for continued assessment of the duration of induced immunity. by the vaccine and/or naturally,” said the wrote the study authors.

Those reinfected had mild symptoms and none of them were hospitalized or died. The study also found that people reinfected with the BA.2 infection had reduced viral loads, indicating some cross-immunity from the first infection.

The UK Health Safety Agency, in a separate study, found 69 cases of people re-infected with BA.2 no more than 90 days after their first infection with Covid. However, no cases of people re-infected with BA.2 after catching BA.1 for the first time were found among the 51 cases for which sufficient information was available. The timing of the first infections and sequencing indicated that their original Covid cases were the delta variant.

Neither study has been peer-reviewed, which is the benchmark for academic publishing. The scientists published their research as quickly as possible due to the urgency of the pandemic.

WHO, in a statement on Tuesdaystated that data from early case studies of reinfection in the general population show that BA.1 infection provides strong protection against BA.2 reinfection.

“It may be that BA.2 has, from his point of view, the unfortunate scenario of entering a population that has a lot of pre-existing immunity that targets him and that may be part of the reason why we don’t see him. grow as rapidly as BA.1 omicron,” said Andrew Pekosz, a virologist at Johns Hopkins University.

Doesn’t seem harsher

A big, real world study in south africa which has not yet been peer reviewed found that BA.2 causes a disease similar to BA.1 omicron, which generally does not make people as sick as the delta variant. In other words, BA.2 generally does not cause more severe disease.

South Africa’s National Institute of Communicable Diseases found that 3.6% of people with BA.2 were hospitalized, compared to 3.4% of people with BA.1. About 30% of patients hospitalized with BA.2 were critically ill, compared to 33% of patients hospitalized with BA.1. The study is based on more than 95,000 people who tested Covid from December to January.

“BA.2 in terms of clinical severity behaves very similarly to BA.1 with reduced clinical severity compared to previous variants and in particular delta,” said Cheryl Cohen, one of the study authors. , during a press conference broadcast live on YouTube earlier this month.

WHO officials have repeatedly said there is no indication that BA.2 is more serious. Cohen said the data from South Africa is reassuring, but she also cautioned against drawing conclusions about other countries based on the results.

“We have to be careful in extrapolating to other places, especially to other countries where most immunity comes from vaccination, unlike South Africa where most immunity comes from a natural infection,” Cohen said. “Natural infection could potentially provide more robust protection against BA.1 and BA.2 than vaccination. »

At least one study found that mutations in the spike protein BA.2 caused more severe lung infection in hamsters than BA.1. The virus uses the spike to invade cells, and vaccines target this protein to block infection. The team of Japanese scientists who conducted the research stated that the WHO should consider designating BA.2 as a separate variant of concern accordingly.

Suthar, Emory’s virologist, urged caution when interpreting the results of the Japanese study because it does not use the real version of BA.2. He said mutations on a single component of the virus, like the spike, do not necessarily determine whether the virus is more severe.

The study was not peer reviewed and one of the scientists said the results might not hold up in the real world since they used a technical version of BA.2 to test their theory. The team took the spike protein from BA.2, swapped it out and placed it on the original Wuhan virus, according to Takashi Irie, one of the study’s authors. Irie, in an email to CNBC, acknowledged that more reports showed no increase in severity of BA.2 compared to BA.1.

“Therefore, the finding from our study that BA.2 is more pathogenic than BA.1 may not reflect the actual results of the isolated virus,” Irie wrote. However, he said the study results indicate that mutations on the BA.2 spike are capable of causing more severe infection.

A separate study of Japan, which isolated the BA.2 virus from a traveler who arrived in Japan from India, found that the subvariant had a similar level of severity to BA.1 in mice and hamsters. The study was also not peer-reviewed.

the WHO Covid Variant Advisory Group reviewed both the South African and Japanese studies, among others, before determining that BA.2 should remain classified as an omicron rather than designating it as a separate variant of concern. This suggests that the WHO does not currently consider BA.2 to be a greater global health threat than omicron in general.


The original omicron BA.1 strain demonstrated substantial ability to evade vaccine-induced antibodies, leading to many breakthrough infections in the recent surge. Danish scientists have found that BA.2 is better at evading vaccine protections than BA.1, according to a published study last month.

However, vaccinated people who get breakthrough infections don’t transmit the virus to others as easily as unvaccinated people, the study found. This is likely because vaccinated people have a lower viral load than people who did not receive their shots, the scientists said. In other words, vaccines always help reduce the spread of the virus.

Scientists at Beth Israel Deaconess Medical Center in Boston found that BA.2 evades antibodies from two doses of Pfizer slightly more than BA.1. Neutralizing antibody levels were approximately 1.4 times lower against BA.2, according to a study published in early February.

“BA.2 evades antibodies from Pfizer vaccines the same way BA.1 does, maybe a little more but not much more,” said Dan Barouch, study author and principal investigator at Harvard’s Center for Virology and Vaccine Research. Barouch also helped develop Johnson & Johnson’s Covid vaccine.

Barouch said vaccinated people infected with BA.1 also developed robust antibodies against BA.2. “This would suggest that since BA.1 omicron has been so prevalent, these people probably have a substantial degree of immunity to BA.2,” he said.

The UK Health Security Agency, in a report published on February 24, also found that the efficacy of two doses of vaccine against symptomatic disease had declined to similar levels against BA.1 and BA.2. Booster injections increased protection to 69% against BA.1 and 74% against BA.2 two weeks after the third dose, according to the British study.

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