With omicron spreading globally at a dizzying pace, scientists are scrambling to learn as much as they can about the latest worrisome variant of the coronavirus. First spotted in South Africa and Botswana at the end of November, omicron is already poised to soon become the dominant variant — dethroning delta — in some regions, public health officials warn. In a few places, it already has. So answers, including how sick does omicron make people and how well do vaccines hobble it, can’t come fast enough.
A rising tide of data on omicron is beginning to provide a glimpse at what’s ahead as we enter year three of the global pandemic, though many questions linger. And with many people preparing to gather with family and friends for holidays, experts are bracing for yet more case surges, compounded by already high infection rates in some countries linked to the still-prevalent delta variant.
Omicron’s collision with the holidays and travel is “a perfect storm,” Thomas Denny, a vaccine expert at Duke University, said December 16 in a call with journalists. At this point, even vaccinated people should be taking precautions, such as wearing masks indoors and testing before family gatherings, he said. “This new variant has thrown us a curve ball at the worst possible time.”
Still, amid the worries, there are positive signals that vaccines can still protect people from the worst of COVID-19. As many countries hurtle toward a season of omicron, here’s what researchers are learning so far.
Omicron is spreading fast, already outstripping delta in some countries.
Omicron’s high number of mutations in important viral proteins, and signs that the variant was behind a surge of COVID-19 cases in South Africa, quickly raised red flags, hurling the pandemic into yet another tsunami of uncertainty (SN: 12/1/21).
In the weeks since omicron emerged, the variant has been identified in more than 85 countries. Some, like Denmark, have identified some cases that date before South African researchers revealed omicron’s presence to the world — a hint that the variant had already slipped across borders from wherever it originated before its November discovery. In many of these places, omicron infections are rising fast.
Omicron is responsible for nearly all new COVID-19 cases in South Africa, and is already the predominant version of the coronavirus in London. The European Centre for Disease Prevention and Control estimates that omicron will be the most common variant across the European Union by mid-January.
In the United States, omicron now appears to reign. The variant was responsible for an estimated 73.2 percent of new infections across the country for the week ending December 18, according to the U.S. Centers for Disease Control and Prevention’s predictions. That’s up from an estimated 12.6 percent the previous week and 0.7 percent the week ending December 4. Omicron now accounts for an estimated 92 percent of new cases in New York and New Jersey and 96.3 percent in Washington, Oregon and Idaho.
Previous data suggested that estimates of omicron’s prevalence from earlier in December were lower. It takes time to collect and analyze viruses from patient samples, Bronwyn MacInnis, director of pathogen surveillance at the Broad Institute of MIT and Harvard, said in a December 14 call with journalists. So the numbers can “change quickly as more data comes in off machines in real time.”
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With that in mind, omicron is likely to worsen the surge that is unfolding across the United States. Some places, including New York City, are already seeing large spikes in COVID-19 cases with numbers rising fast. It currently takes about two days for the number of omicron cases to double, CDC director Rochelle Walensky said December 15 in a White House news briefing. Highly infectious delta, in comparison, doubled every two weeks at the beginning of its surge in the United States (SN: 7/2/21).
It was a huge question whether omicron would compete with delta for global dominance. Now, some real-world studies show that omicron is coming on strong in many regions. Preliminary data from the United Kingdom show that omicron is around 3.2 times as likely to spread among households as delta is, researchers with Public Health England, a U.K. health agency, reported December 9.
And people exposed to omicron may get sick faster — and therefore be able to spread the virus sooner — than people exposed to other variants. An analysis of an omicron outbreak at a company Christmas party in Norway found that the median time that a person exposed at the party developed symptoms was three days, researchers reported December 16 in Eurosurveillance. It takes slightly longer for delta infections to cause symptoms — around four days — and about five days for non-delta variants.
The reasons behind omicron’s swift spread are still fuzzy. It could be because omicron is more transmissible than delta or because it can dodge parts of the immune response. Or, more likely, it could be a mixture of both, says Kartik Chandran, a virologist at Albert Einstein College of Medicine in New York City. Some preliminary studies done in lab-grown cells hint that omicron may turn out to be more transmissible than delta, though how much more is unclear. One reason may be because the new variant might make more copies of itself inside host cells than other variants do.
Omicron may also replicate particularly well in bronchial cells — which line the tubes that deliver air to the lungs — compared with how well it grows in lung tissue, researchers reported December 15 in preliminary data from the University of Hong Kong. If the virus is growing well in bronchial cells, symptoms like coughing could release a lot of viruses into the air.
It’s still unclear if omicron causes milder disease.
The Hong Kong results may be a sign that omicron might be less likely than variants like delta to invade the lungs of infected people and cause severe illness, but that’s far from definitive. “I don’t think you can really say that the virus is going to be less virulent based on that data alone,” Chandran says. “We’re going to have to wait and see what happens to people.”
There are some hopeful hints from South Africa that omicron might cause less severe disease than what delta causes. But experts caution that it’s far too early to make solid conclusions.
“We should not be lulled into any type of complacency,” Ryan Noach, CEO of Discovery Health, a health insurance provider based in South Africa, said December 14 in a news conference.
The optimism comes because hospitalizations in South Africa aren’t rising as fast as they did in previous surges. What’s more, anecdotal reports from the country suggest that fewer hospitalized patients in the current wave rely on medical interventions to breathe, such as supplemental oxygen.
That information, however, comes with a massive caveat: More than 70 percent of people there have been exposed to the coronavirus in the last 18 months, Noach said. Protection provided by previous infections, or vaccinations, could be the reason people there tend to have milder symptoms.
Experts need to see what happens in other parts of the world before concluding that omicron is a less virulent virus than other variants, Glenda Gray, president and CEO of the South African Medical Research Council, said at the December 14 news conference. Monitoring the severity of COVID-19 cases in places with low vaccination rates and low infection rates will be particularly informative, she said.
A study from the United Kingdom found that so far there is no indication that omicron might cause milder, or more severe, COVID-19 than delta, researchers report December 17. Data on hospitalizations there, however, are still limited.
Even if omicron is ultimately linked to milder disease, that doesn’t mean it isn’t dangerous. More infections overall mean more hospitalizations and more deaths, even if the severe outcomes are a smaller proportion of overall omicron cases than with delta.
In the United States, where delta dominated until recently, the two variants are colliding — and that’s raising fears of this latest wave turning into a tsunami in some places.
“Our delta surge is ongoing and, in fact, accelerating,” Jacob Lemieux, an infectious diseases physician at Massachusetts General Hospital and Harvard Medical School in Boston, said in a December 14 call with reporters. “On top of that, we’re going to add an omicron surge. That’s alarming because our hospitals are already filling up. Staff are fatigued. We’re almost two years into the pandemic, and there may be limits on capacity to handle the kinds of caseloads that we see from an omicron wave superimposed on a delta surge.”
Omicron can evade some antibodies.
Even before omicron began to spread widely, scientists were immediately concerned that it might be able to hide from some virus-attacking antibodies. Recent studies suggest that yes, the virus can evade parts of the immune system. But as our immune defenses are multipronged, it’s not all doom and gloom.
That worry initially came because omicron sports more than 50 mutations in various viral proteins. More than 30 of those changes are in the coronavirus’ spike protein, which helps the virus break into cells and is a major antibody target.
Since December 7, a slew of studies that have yet to be reviewed by other scientists has come out in support of the hypothesis that omicron can evade the immune response, showing that some antibodies don’t recognize omicron very well.
For example, among people vaccinated with two doses of the COVID-19 vaccine made by Pfizer and its German partner BioNTech, levels of immune proteins called neutralizing antibodies that stop the virus from infecting new cells were 41 times lower compared with antibodies against an older version of the virus that rose to prevalence in mid-2020, researchers report in a preliminary study posted December 11 at medRix.org. Previously infected people who have been vaccinated, on the other hand, have a leg up (SN: 8/19/21). The study showed that antibody levels against omicron were lower in people who had received two doses of Pfizer’s shot than in similarly vaccinated individuals who had recovered from a previous infection.
The findings are in line with those from multiple other studies that include other vaccines approved in the United States — Moderna’s and Johnson & Johnson’s — as well as ones used globally. The overall magnitude of the antibody drop differs from study to study, but all show the same pattern. Antibodies from people who had previously been infected but not vaccinated also perform poorly against omicron.
What’s more, omicron’s spike mutations may make treatments using lab-designed antibodies, called monoclonal antibodies, less effective, researchers report in a preliminary study posted December 14 at medRxiv.org. Out of nine monoclonal antibodies currently in clinical use, only two neutralized omicron in lab-grown cells.
The good news is that a different treatment, a yet-to-be-approved pill from Pfizer called Paxlovid, should still work against the new variant, the company said in a December 14 news release.
T cells may fare better against omicron than neutralizing antibodies.
Still, neutralizing antibodies that circulate in the blood are only one small piece of the immune response. Another arm appears largely undamaged.
Immune cells called T cells can either raise the call to arms when they detect the coronavirus or are capable of killing infected cells. T cells patrol the body searching for signs of the coronavirus. The cells identify fragments of viral proteins by doing cellular handshakes to check if cells are sending up red flags that the coronavirus has invaded. A red flag kicks the immune response into high gear.
It seems that many of the viral fragments that T cells recognize aren’t the parts of omicron with mutations, researchers report in a preliminary study posted December 9 at bioRxiv.org, meaning the immune cells will probably still help protect people from getting really sick.
Omicron seems more likely to cause reinfections than delta.
Immunity against infection wanes in the months afterward. That combined with the immune evasiveness of omicron has raised the odds that previously infected people might get infected again.
Data from the United Kingdom, for instance, suggest that recovered people are five times as likely to be infected by omicron as by delta, researchers from Imperial College London report December 19.
The same appears to be true in South Africa. People who caught the virus in South Africa’s first wave, which was driven by a variant called D614G, are 73 percent as likely to get reinfected with omicron as people without known prior infections. That’s higher than the 29 percent higher risk for recovered people in September and October 2021, when delta was prevalent there. Individuals infected in the second wave caused by the beta variant face a 60 percent higher risk, up from 27 percent in September and October.
Vaccines may be less effective against omicron, but boosters offer hope.
Early studies suggest that vaccines will still protect us, especially after getting a booster shot.
Lab-based studies of neutralizing antibody responses are a hint that protection from vaccines or previous infection might be diminished. Many of these same studies suggest that a third dose boosts antibodies back up to levels that should be protective against omicron.
Boosters can even provide more protection than the original shots because the body churns out antibodies that have evolved to better recognize the virus every time we’re exposed to its proteins, Chandran says. So after a boost, the body doesn’t just make more antibodies, they’re better ones, too (SN: 11/24/20). But because the immune response to infections is complex and varies from person to person, experts rely on studies from people in the real world to know for sure.
A study in South Africa, for instance, found that the effectiveness of two doses of Pfizer’s vaccine at stopping infection dropped from 80 percent pre-omicron to 33 percent during the omicron wave. There was a less dramatic drop in the shot’s effectiveness at preventing hospitalization. Before omicron, the jab was 93 percent effective; it decreased to 70 percent amid the new surge.
“It’s very heartening to see these results,” Gray, of the South African Medical Research Council, said at the December 14 news conference. Though the study didn’t look at the effect of booster shots, another dose should bring the vaccines’ effectiveness back up, she said. Analyses for comparing one or two doses of J&J’s COVID-19 vaccine are ongoing and should have results soon, Gray added.
The findings are similar to early estimates out of the United Kingdom, which show Pfizer’s two-dose shot is around 30 percent effective against symptoms. A booster dose increased the effectiveness to between 70 percent to 75 percent, according to data from Public Health England. Still, there’s a lot of uncertainty because those findings are based on low numbers of cases. As time passes and more people get infected, researchers will get better estimates.
In the meantime, the worry about omicron has sparked a flurry of activity. People around the globe are upping their layers of protection with vaccinations, masks and pre-holiday COVID-19 tests. Experts expect that vaccines will largely keep vaccinated people out of the hospital. But with many people still unvaccinated across the United States, only time will tell whether the beginning of 2022 will be as devastating as the start of 2021.
“We are now waist-deep in the omicron wave,” infectious diseases physician Lemieux said in a December 20 call with journalists. The big question is how large the country’s omicron wave will be and what impact it will have on the health care system.