Is Omicron really less severe than Delta? Here’s what the science says.

Still, different strains of SARS-CoV-2 share important similarities, and much of the basic public health advice—get vaccinated, wear a mask—remains the same. Here’s what the latest research says about staying safe in the age of Omicron.

Is Omicron really causing less severe disease than Delta?

Multiple lines of evidence from various parts of the world suggest that the Omicron variant causes a less severe form of COVID-19. In South Africa, where Omicron was first detected in November 2021, a private health insurance administrator reported in mid-December that adults with Omicron were 29 percent less likely to be hospitalized, compared with adults infected several months earlier. In the U.K., the rate of hospital admission among people who went to the emergency room with Omicron was a third of what it was for Delta, according to a summary of research from the U.K. Health Security Agency released on December 31, 2021.

As of early January, U.S. adults with Omicron were less than half as likely to visit the emergency room, be hospitalized, or be put on a ventilator, according to preliminary work by researchers from Case Western Reserve University School of Medicine. Their study, which has not yet been peer-reviewed, examines data for more than 14,000 patients and accounts for their vaccination status and any pre-existing conditions.

A shift in symptoms reflects those trends, del Rio says. In the hospital, patients are showing up less often with pneumonia-like symptoms and hyperactive immune systems, as seen in previous waves. Instead, they’re more often presenting with congestion and scratchy throats. “In Omicron, the symptoms are more like a head cold,” he says.

Does severity differ based on age or preexisting conditions?

Omicron appears to be less severe than Delta in all age groups, even in adults older than 65 and in children too young to be vaccinated, according to the Case Western study. Still, as with other health issues, age remains a factor, del Rio says. “For any disease, if you’re older, you’re going to do a lot worse,” he says.

People with underlying conditions or compromised immune systems also remain more vulnerable, as do people who are unvaccinated. Although current vaccines are less effective at preventing symptoms from Omicron than from Delta, the U.K. report found that people who were fully boosted were up to 88 percent less likely to be hospitalized with Omicron compared with unvaccinated people. Hospitals around the country report that unvaccinated patients make up the majority of people now in intensive care units.

Regardless of age or health status, people infected with Omicron can feel terrible even if they don’t have to go to the hospital, and the variant continues to hospitalize and kill many people, emphasized Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, in a virtual press conference last week.

Why is Omicron dangerous if it’s less severe than Delta?

Omicron is between two and four times more contagious than Delta, according to a Danish study that has not yet been peer reviewed. It’s also better at evading the antibodies triggered by vaccines, which is why it’s causing more breakthrough infections. As a result, more people are getting sick and showing up at hospitals, where more staff are calling in sick, del Rio says.

Omicron has 36 mutations within its spike protein, which is the part essential for anchoring the virus on human cells and infecting them. Though none are peer reviewed, at least half a dozen studies using small animal models—such as mice and hamsters—and laboratory cell cultures have started to reveal how those mutations alter the way that Omicron enters cells and replicates, says John Moore, a vaccine researcher and virologist at Weill Cornell Medicine in New York.

Unlike previous variants, Omicron appears unable to infect lung cells as efficiently, which in turn makes it less damaging and the symptoms less severe. Viral loads are significantly lower in the lungs of Omicron-infected rodents in some studies. But in the upper respiratory tract, which includes the nose and sinuses, Omicron seems to replicate more than a hundred times faster than Delta.

That mix of changes—the preference for the upper airway, better immune invasion, and high transmissibility—reflects how evolution pushes the virus to ensure its own future by replicating and spreading even when that does not make individuals sicker.

“It kind of doesn’t matter to the virus, once it’s replicated, whether that person lives or dies as long as it can get to the next host,” Moore says. “It’s all about genome replication.”

What do these changes mean for at-home testing?

All strains of the SARS-CoV-2 virus can infect cells in the mouth, and Omicron may be particularly abundant there compared with other variants, early evidence suggests. In one study that has not yet been peer reviewed, researchers in South Africa tested 382 people who were not sick enough to be hospitalized but still had COVID-19 symptoms. They found that in those with Delta, nose swabs were more accurate, but for Omicron, saliva tests worked best.

Other studies also suggest that rapid antigen tests that rely on nasal swabs might be especially slow to identify infections with Omicron. In one study posted last week that has not yet been peer reviewed, researchers looked at samples from 30 people who tested positive for COVID-19 around the United States during outbreaks in early December. For most cases of Omicron, PCR tests showed positive days before a rapid test did. Those results echo what people have been reporting on social media, says study coauthor Anne Wyllie, a medical microbiologist at the Yale School of Public Health in New Haven, Connecticut.

Given the growing evidence for Omicron’s prevalence in spit, social media has been full of DIYers and researchers advocating that people swab their throats with at-home test kits. Wyllie has even tried it herself using the swab from a rapid test. The result was negative, but she felt more confident that it was a true negative than if she’d only swabbed her nose.

“It’s not what’s been authorized by the FDA, and it’s a very tricky topic to speak out on because of that,” she says. That’s why many other experts are hesitant to recommend the off-label use. While throat swabs might eventually become part of the testing equation, rapid tests were designed for noses, not throats, says Jill Weatherhead, an infectious disease expert at the Baylor College of Medicine in Houston.

“At this point, the recommendation would be to continue to do the test as they’ve been designed to be done until further testing has been shown that it’s effective,” Weatherhead says.

Does double masking help protect against Omicron?

The Centers for Disease Control and Prevention does not currently recommend double masking or the use of specific masks. But other countries, including Austria, France, and Germany, have upgraded their guidelines to recommend medical-grade varieties, such as surgical masks or N95s. And some U.S. experts have spoken out in favor of higher quality masks.

One study found that, if fitted correctly, N95s block an average of 90 percent of exhaled particles, while surgical masks blocked 74 percent. That can make a substantial difference in community spread. In Bangladesh, an intervention boosted the percentage of people wearing surgical masks in some villages from 13 percent to 42 percent. Researchers then found an 11 percent drop in COVID-19 symptoms, with bigger gains in older groups. Evidence on cloth masks is mixed, but wearing a cloth mask over a surgical mask can block more than 85 percent of cough particles, according to some research.

Experts recommend choosing your mask based on the situation you’re in. In social situations, Moore wears a cloth mask decorated with the logo of his favorite soccer team, Liverpool. When walking around at work or in stores, he wears a thicker cloth mask that he finds comfortable. Del Rio says he wears an N95 whenever he’s with patients. But masking alone won’t protect you from Omicron, he adds. “This is not about some magic bullet, this is about a combination effect,” he says. “If you’re vaccinated and you’re boosted and you’re wearing a good-fitting mask, you can spend a lot of time with somebody.”

Do we still need to disinfect surfaces, stand further away from each other, or alter any other aspect of personal hygiene?

Like prior variants, Omicron is primarily airborne, and experts agree that wiping down surfaces is probably more trouble than it’s worth. “Transmission from surfaces is low,” Wyllie says. Given “the time, energy, money, resources and mental health put into that kind of concern—you’re better spending that on hand-washing, social distancing, and mask-wearing.“

Also, the six-foot rule is more of a reminder that being close to an infected person increases the risk of transmission, says Abraar Karan, an infectious diseases doctor at Stanford University in Palo Alto, California.

“Transmission can happen beyond six feet of distance, for sure,” he says. “However, distance makes transmission less likely, as aerosols get diluted with further distance.” Your risk also depends on ventilation, what kinds of masks people around you are wearing, and other factors.

Is long COVID still a risk when it comes to Omicron?

It’s too soon to know, and it likely will be months before researchers can tell if Omicron causes symptoms that stick around for the long-term. But some experts are hopeful that long lasting consequences will be less common because of Omicron’s tendency to stay out of the lungs, and because more people are getting vaccinated, which can help prevent infections and lower risk of developing a number of symptoms. “I would suspect we will still see cases,” Wyllie says. “But because we have far more people now vaccinated, I am hoping we see less long COVID-19.”

Editor’s Note: This story has been updated to include more detail about John Moore’s mask preferences.