Although BA.2 has just hit the US stage, it has had outstanding appearances in many other parts of the world, including Southeast Asia and the Western Pacific, and is completing its European tour. According to the World Health Organization, BA.2 is also the leading cause of Covid-19 worldwide, surpassing two other Omicron genera, BA.1 and BA 1.1, to become the dominant strain. Since its acquisition, international cases – which have been declining since the first week of January – are rising again. In the United Kingdom, which has a more vaccinated population than the United States, a combination of lifting restrictions, declining immunity and an even more contagious version of the virus has created a new BA.2 wave. Covid-19 cases, hospitals and deaths have been on the rise since late February and now, the weekly average of new cases is around where they were at the end of January. However, BA.2 infections have not reached the peaks observed with BA.1. The number of cases seems to be declining in the UK, although hospitalizations and deaths continue to rise. Throughout the pandemic, the United States followed the United Kingdom for about three weeks, so when cases began to rise there, health officials here alerted. In the US, BA.2 has been gaining momentum since late January and case numbers have risen. However, this leveling hides regional differences. In 13 states, the average weekly number of new cases is rising and has stopped falling in 14 others, according to data collected by Johns Hopkins University. It is not yet clear what this minor variant will do in the US. Even experts do not know exactly what to expect. “We are not immune to what is happening in Europe,” said former CDC director Dr. Tom Frieden, who is now president and CEO of the non-profit organization Resolve to Save Lives. “In Europe, you see BA.2 dominating and leading to a resurgence, and the chances of that not happening in the US are really very low,” Frieden said. “I think part of the reason we’re making it is that we’re going to start climbing again.” Frieden does not think it’s a coincidence that the US Food and Drug Administration approved additional reinforcements for Americans aged 50 and over on Tuesday, the same day that the CDC ruled that BA.2 was dominant. But one can guess how high the cases will go, if many people will need hospital treatment and if the nation will continue to see astonishing numbers of deaths.
Facing an “intimate uncertainty”
Most predictions for BA.2 in the US were not tragic. The University of Washington’s Institute for Health Measurement and Evaluation forecasts for Covid-19, updated last week, predict that BA.2 will not lead to a new rise in the US. But they say we can see something like what happened in South Africa, where BA.2 quietly replaced BA.1’s cousin as the main cause of Covid-19 infections – with no increase in cases or deaths. Instead, it pulled the Omicron down, causing a long tail. Michael Osterholm, who heads the Center for Infectious Diseases Research and Policy at the University of Minnesota, called the coronavirus waiting game we play every few months “an intimate uncertainty.” He dedicated his latest podcast to “all of us who remain confused about what the immediate or intermediate future looks like with Covid.”
How strong is our immune wall?
There are many reasons why it is difficult to know what BA can do.2. The CDC estimates that 37 million Americans – about 1 in 11 – contracted Covid-19 during the winter, during the first Omicron wave. Many more are immune to vaccines and boosters. So, based on random blood samples, the CDC says that 95% of Americans may now have some degree of immunity to Covid-19. Dr. Jorge Salinas, an infectious disease specialist at Stanford University, calls it the immune wall. “This gives us some protection against future increases,” he said. “However, this wall wears out over time. The longer it lasts after a wave or after vaccination, the greater the decay of the wall.” Studies have shown that BA.2 avoids our vaccinations as did the original Omicron, so boosters are needed to restore protection against these variants. But less than half of the US population aged 12 and over has received a recommended third dose. The biggest concern is adults over the age of 65, as they are most likely to become seriously ill with Covid-19. One in three people over the age of 65 in the United States has not received a critical third dose of the vaccine. “The real problem is that so much of our population is under-vaccinated elderly,” Frieden said. “This is our Achilles heel.”
Questions about re-infection
The other variable is in the virus itself. Omicron dropped our immune system defenses for a loop. It was so different from the coronavirus strains that appeared before that many people who had Delta or other early strains became infected again. BA.2 has about 40 amino acid changes from Omicron’s BA.1, which makes it as different from its cousin as Alpha, Beta and Delta were. Some have wondered if BA.2 could re-infect people who had BA.1. A large study from Denmark shows that such infections are possible but rare. A survey of more than 1.8 million infections found only 1,739 cases in which people tested positive for Covid-19 twice in a two-month window. Of these, 47 were BA.1 infections followed by BA.2. When researchers looked more closely, they found that these types of infections tended to occur in young and unvaccinated people, especially children. And their symptoms tended to be mild. The study was published as a preprint, which means it has not yet been reviewed by external experts and has not been published in a medical journal.
Studies show high viral loads
BA.2 is highly contagious. Some epidemiologists have said that the basic number of reproduction can be up to 12, which means that each patient infects an average of 12 others. This would bring it to the same level as measles, which is also transmitted through the air. The baseline reproduction number for BA.1 is estimated to be around 8. In a pre-print study from Sweden, researchers measured virus levels in smears from the back of the nasal cavity. They found almost twice as much viral RNA in samples of patients with BA.2 as in those tested positive for BA.1, “showing a significant difference in viral load”. The viral loads were about the same for Delta and BA.1 infections, they said, “while the increase in viral load in BA.2 cases was astounding.” Another pre-print study from Qatar highlighted this difference, too. Laith Abu-Raddad, professor of population science at Weill Cornell Medicine-Qatar, has studied the effectiveness of vaccines and boosters against BA.1 and BA.2. A significant difference between the two infections is a person’s viral load, he said. “It is definitely much higher” with BA.2 versus BA.1, he said. His study found that it was “almost 10 times higher”. Instead of penetrating deep into the lungs, as Delta did, Omicron strains look much more focused on the upper airway, where the nose meets the back of the neck, Abu-Raddad said. He believes that because the infection accumulates there, it also helps to spread effectively when people talk, cough or sneeze.
A bright spot?
Perhaps a bright spot in Figure BA.2 may be the severity. Although animal studies have shown that BA.2 infection was not entirely mild, data on human infections from the United Kingdom, Denmark and South Africa show that BA.2 is less likely to lead to hospitalization compared to with BA.1. This week, the UK Health Insurance Agency updated its data on the effectiveness of the BA vaccine.2. Up to 14 weeks, boosters were still 90% effective in preventing serious illness in people over the age of 65, suggesting an important way to make sure BA.2 does not put us down.
