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BA.2 more contagious, but vaccinated less likely to spread it, study finds

A healthcare professional administers a Covid-19 test at the test site in San Francisco, California, USA, on Monday, January 10, 2022.

David Paul Morris | Bloomberg | Getty Images

The Omicron BA.2 subvariant is inherently more contagious and better at avoiding vaccines than any other Covid strain, but vaccinated humans do not transmit it as easily as unvaccinated, according to a Danish study published Sunday.

The new subvariant, which has quickly become dominant in Denmark, spread more easily across all groups regardless of gender, age, household size and vaccination status, the study found. The probability that the subvariant would spread within a household was 39% for BA.2 compared to 29% for BA.1, the original omicron subvariant that was dominant worldwide per year. January 19, according to the World Health Organization.

The study, led by a team of researchers affiliated with, among others, the University of Copenhagen and the Ministry of Health, has not yet been sent for peer review. Researchers have published their findings before being examined by other experts in the field due to the urgent nature of the pandemic.

BA.2 is more contagious than the original BA.1 subvariant among both vaccinated and unvaccinated individuals, but the relative increase in susceptibility to infection was significantly greater in vaccinated than unvaccinated individuals. This indicates that it is even better at escaping vaccine protection than BA.1, which was already significantly more contagious than any other Covid variant, according to the study.

Transmission rates among unvaccinated individuals were higher with BA.2 compared to BA.1, indicating that unvaccinated individuals carried a higher viral load with BA.2. Although fully vaccinated people are more likely to catch BA.2 than the previous strain, they are less likely to spread it to others, researchers found.

People who received a booster were even less likely to transmit the virus than people who were fully vaccinated.

“This indicates that following a breakthrough infection, vaccination protects against further transmission, and more for BA.2 than BA.1,” the researchers found.

The study also noted that the higher susceptibility to infection and greater transmission of BA.2 are likely to result in more widespread spread of the virus among unvaccinated children in schools and day care centers.

It is reassuring that BA.2 is generally milder compared to the delta variant, the researchers said, and the vaccines protect against hospitalizations and serious illness.

“The combination of high prevalence of a relatively harmless subvariant has raised optimism,” the researchers wrote, noting the importance of keeping a watchful eye on BA.2.

More than half of U.S. states have detected BA.2, with a total of 194 confirmed cases nationwide so far, according to a global database of Covid variants. The Centers for Disease Control and Prevention said in a statement Friday that BA.2 is currently circulating at a very low level in the United States.

“Currently, there is no evidence that the BA.2 genus is more serious than the BA.1 genus,” said CDC spokeswoman Kristen Nordlund.

Denmark, a country of 5.8 million people, reports an average of about 46,000 new cases a day, according to data collected by Johns Hopkins University, an 18% increase over the past week and almost double the level two weeks ago . The Scandinavian nation on Monday reported 80 new admissions for a total of more than 1,000 people currently admitted with Covid.

Denmark reports an average of about 19 Covid deaths a day, which is increasing, but well below the pandemic of about 36 daily deaths recorded last winter, according to the Hopkins data.

Troels Lillebæk, chairman of Denmark’s Covid variant monitoring committee, said that the health system in his country may be able to handle hospital admissions, but nations with lower vaccination rates may face a tougher road ahead.

“If you are in a community or live in a country where you have a low vaccination rate, then you will definitely have more hospital admissions and more serious cases and then more in the intensive care unit,” said Lillebæk.

In Denmark, more than 80% of the population is fully vaccinated and more than 60% have received a booster dose. In the United States, 63% of the total population is vaccinated, and about 41% of those vaccinated have a booster, according to the CDC.

The World Health Organization has not yet labeled BA.2 as a separate variant of concern from omicron. However, WHO officials have warned that new variants will almost certainly emerge when omicron spreads at an unprecedented rate around the world. Maria Van Kerkhove, WHO’s Covid-19 technical director, said last week that the next variant would be more transferable, but it is an open question whether it will be more serious.

“The next variant of concern will be more appropriate, and what we mean by that is that it will be more transferable because it will have to overtake what is currently circulating,” Van Kerkhove said. “The big question is whether future variants will be more or less severe.”

The CEOs of Pfizer and Moderna are also concerned that a new variant may emerge as immunity to vaccines diminishes over time. Pfizer is conducting a clinical trial with an omicron vaccine in people aged 18 to 55. The company expects to have the shot ready by March. Moderna has launched a clinical trial with an omicron-specific booster dose in adults over 18 years of age.

Real-world studies from around the world – including the US, UK and South Africa, among others – have found that omicron generally does not make people as sick as the former Delta variant. However, Omicron is spreading so fast that it is burdening already congested hospitals.

WHO and White House Chief Medical Adviser Anthony Fauci has said it is unlikely to exterminate Covid. However, the WHO’s Director for Europe, Hans Kluge, said last week that omicron “offers plausible hope for stabilization and normalization.”

Public health leaders and scientists around the world hope that vaccination and mass exposure to omicron will create so much immunity in the population that fewer people will be susceptible to the virus, which may make it less disruptive to society. However, Fauci has said that there is no guarantee that the omicron variant will help end the pandemic.

“I would hope that is the case. But that would only be the case if we do not get another variant that evades the immune response from the previous variant,” Fauci told the World Economic Forum earlier this month.

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