Covid-19 in the US: As BA.2 subvariable grows, experts look to other countries to predict its impact here – zimo News


BA.2 caused about 35% of cases in the U.S. last week, up from 22% the week before, according to new estimates released Tuesday by the U.S. Centers for Disease Control and Prevention.

Meanwhile, new Covid-19 cases have remained stable or rising in about 19 states, according to data from Johns Hopkins University.

“I wouldn’t be surprised if we see a slight uptick,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in an interview with U.S. media on Tuesday. Washington post“I really don’t think there’s going to be a major push unless there’s a huge change,” he said.

In the UK, BA.2 now accounts for 85% of new infections, with the number of cases increasing by 20% each week. Hospitalizations were up about 22% from the previous week. According to the number of deaths recorded in the 28 days after testing positive for Covid-19, there has been an increase of about 17%. Recent government data.
On Tuesday, the Institute for Health Metrics and Evaluation at the University of Washington said its models did not predict a further increase in Covid-19 cases, “similar to what we’ve seen in parts of Europe,” said Ali Mokdad, a professor of global health. On the man-machine interface, on twitterInstead, he said, their modelling suggests a further steady decline in the spread of Covld-19 in the U.S. after the end of March.

Highly contagious, but not more serious

BA.2 is technically classified as part of the Omicron virus family, but genetically this strain is very different, having about 40 mutations from its cousin BA.1. This makes it completely different from the original Omicron, just as Alpha, Beta and Delta are different from each other.

It’s more contagious than Omicron’s BA.1, which is already a highly contagious virus with a basic reproduction number, or R-naught, of about eight, says epidemiologist William Hanage of the TH Chan School of Public Health. This means that an infected person can, on average, transmit the disease to 8 other people.

Epidemiologist Adrian Esterman of the University of South Australia pegged BA.2’s basic reproduction number at around 12. “This puts it very close to measles, the most contagious disease we know of,” he tweeted on March 10. .

Although BA.2 is more contagious, it does not appear to cause more severe disease. Although it escaped some immune protection from previous vaccinations and infections, it did not appear to be more effective than BA.1.

On a population level, Omicron is more manageable than Delta, but he’s not harmless, Hanage said.

“The reason Omicron BA.2 and BA.1 are problematic is the sheer number of infections they cause,” Hanage said.

Will BA.2 cause tides or ripples?

The contours of BA.2 waves vary by country. BA.2 led to a surge in cases and deaths in Hong Kong and many older adults were hesitant to get vaccinated, but in South Africa it arrived on the heels of the country’s BA.1 surge and it barely made a ripple – causing cases to level off rather than climbing.

What BA.2 can do in the United States remains an open question.

Britain offers some clues about past variant trajectories. But there are some key differences.

With their support, the UK has a higher vaccination rate than the US. Among those 12 years and older, 86 percent received two doses of the vaccine, while more than two-thirds received a third or booster dose. In the U.S., 74% of people 12 and older received two doses of the vaccine, but only 46% received a booster dose.

But the UK has its own challenges, said Dr. Carlos Del Rio, an infectious disease expert and deputy executive dean of the Emory School of Medicine. “Their population is much older than ours,” he said.

In the UK, 19% of people are over the age of 65, according to a UK government report. In the United States, older adults make up about 16 percent of the population.

While it wasn’t fun at the time, Del Rio said, “the good news is that we got a big push from Omicron in the US. Millions were infected,” he said.

“Between the number of people infected and the number of people who have been vaccinated, we estimate that about 73 to 75 percent of the population has some level of immunity,” he said.

Makes about 25% of Americans susceptible to the BA.2 virus, either because they can’t or don’t make antibodies.

“So I think we’re going to have a surge, but it won’t be a serious surge,” Del Rio said, though he remains concerned that 25 percent of Americans are not protected.

A clue from Qatar

Other interesting clues about the shape of the BA.2 wave come from the Middle Eastern country Qatar, which uses roughly the same combination of vaccines as the United States.

Qatar has had BA.2 as the main virus since Christmas. They also saw a strong surge in Omicron, peaking around mid-January, followed by a sharp decline in cases.

In a recent series of studies, Laith Abu-Raddad from Weill Cornell University in Qatar and her co-authors estimated conservation Conferred by mRNA vaccine and through previous infection.

They found that two doses of the mRNA vaccine provided modest protection against symptoms, ranging from 36% to 50%. But that protection only lasted about four months. After four months, the protection became negligible, and after seven months, their study found that vaccinated people were actually more likely to get sick than unvaccinated people, possibly because they had a false sense of security.

“People who are vaccinated behave differently than people who are not vaccinated. You know, they think they’re protected, so they might be exposed,” Abu-Radad said.

While protection against infection declined sharply over time, the vaccinated person continued to enjoy good protection from hospitalization and death, around 70 to 80 percent, and she again reached around 90 percent, he said.

“The best thing you can do right now is get a callback,” Abu-Raddad said. “The booster brought infection protection back to about 60 percent of what it was before, which is good,” although it did decrease over time, he said. “But what was really surprising about the booster’s effectiveness was that it actually eliminated the risk of hospitalization and death from Covid-19,” he added.

In another study, Abu-Raddad and his team also examined the protective effect of BA.1 infection on BA.2. The protection was even stronger and longer-lasting than two injections of the mRNA vaccine, about 90 percent, he said.

“So that’s actually another reason to think that even if there’s a surge, it’s not going to be as bad as people fear,” he said.

Immunity declines much more slowly after infection, he said. In a new study, they followed people infected with the alpha and beta variants, who still had 50 percent protection against reinfection with Omicron a year later.

The difference, Abu-Raddad thinks, is that immunity from infection stays in the tissues of the nose and mouth, whereas vaccination produces antibodies that rise throughout the body and don’t stay high in those tissues where the virus encounters it . the first time.

Fourth dose for the elderly?

One thing Abu-Raddad’s research can’t reveal is how immune the elderly are. Qatar is a young country. Less than 10% of the population is over 50, so they can’t be sure if the vaccine will continue to be as effective for older people as it is for younger people, he said.

Del Rio suspects that vaccine effectiveness in older people declines faster than in younger people.

“I expect the CDC will recommend a fourth dose of the vaccine for people over 65 in the next week or two. If you’re 65 and get infected, you can still get very serious disease despite the vaccine,” he said. Say.

Source link


Please enter your comment!
Please enter your name here