After Omicron, some scientists foresee ‘a period of quiet’ | Science

Barely 2 months after it began, the Omicron wave is already ebbing in some countries. And although it has sickened huge numbers of people, caused massive disruption, and left many health care workers exhausted, it is also leaving something unusual in its wake: a sense of optimism about the pandemic’s trajectory. In countries where many people have been vaccinated or were infected, scientists say, the worst may finally be over.

“We anticipate that there will be a period of quiet before COVID-19 may come back towards the end of the year, but not necessarily the pandemic coming back,” Hans Kluge, director of the European Region of the World Health Organization (WHO), recently said in an interview. In the United Kingdom, where the Omicron wave crested early, many restrictions were scheduled to be dropped this week, including mandatory masks in public indoor spaces and COVID-19 vaccination passes.

The optimism is shared—although couched in caveats—even by some scientists and public health experts who have stressed the risks of the pandemic from the start and implored politicians to take stricter action. “We have reached a bit of a turning point,” says Devi Sridhar, a global health expert at the University of Edinburgh and an outspoken critic of the U.K. government’s past COVID-19 policies. Not only has the Omicron wave crested in several countries, but its toll has been smaller than feared. And the wave of infections has likely boosted immunity at the population level, which means future waves may wreak even less havoc.

Still, researchers urge caution. Omicron has shown that even a relatively mild wave can put a tremendous burden on health systems and societies as a whole, and it’s unclear how long Omicron immunity will last, how the virus will evolve from here on, and how often breakthrough infections will lead to long-term health problems. “I remain firmly in the camp of: We’ve made great progress but we still have a ways to go before this is truly over,” says Boghuma Titanji, a virologist at Emory University School of Medicine. Besides, “Wealthy countries moving on I fear will push the issues of access to vaccines and therapeutics access down the global priority list,” she says.

For now, Omicron is still spreading worldwide, its impact very different from country to country. Early hopes of a much milder wave were dashed in the United States, in part because its vaccination rate is relatively low. It is seeing more than 2000 deaths daily, as many as during the peak of the Delta wave. Although cases are now declining in New York, Florida, and California, the wave is still building elsewhere.

Countries with high vaccination coverage, such as Denmark, have had staggering numbers of infections as well but with far less severe disease and death. “Overall, the health pressure that we have felt until now has been less than what we feared,” says Henrik Ullum, head of the Statens Serum Institute. In fact, Denmark may lift all pandemic restrictions soon in spite of record-high case numbers. Health systems in many other European countries have been spared, as well.

South Africa, where Omicron was first sequenced, saw cases peak in mid-December. Although deaths are still on the rise, the overall impact has been relatively light as well. Omicron is unlikely to account for more than 5% of COVID-19 deaths in the country, says Shabir Madhi, a vaccinologist at the University of the Witwatersrand, Johannesburg, compared with roughly 50% for Delta. Omicron’s impact is difficult to gauge in other parts of the world, where data are often sketchier.

Omicron’s massive spread leaves Madhi optimistic about the future. A serosurvey he led in Gauteng province, home to one-quarter of South Africa’s population, showed close to 70% of unvaccinated people carried SARS-CoV-2 antibodies at the start of the Omicron wave. In the next survey, he expects that number to have gone up to at least 85%, a level that should prepare South Africa for a post-Omicron future. “There will probably be another wave, but it is extremely unlikely to result in a higher death rate or hospitalization rate than what transpired during the course of the Omicron wave,” Madhi says.

Indeed, data so far suggest the human immune response becomes better and broader with every exposure to SARS-CoV-2’s spike protein. But Omicron’s spike is so different from previous variants’ that it’s not yet clear just how much immunity the Omicron wave will add, or how long it will last, says Leif Erik Sander, an immunologist at the Charité University Hospital in Berlin. And immunity could wane, leading to a new rise in the number of people susceptible to infection.

What the virus will do next is another wild card. What WHO has termed “Omicron” actually comprises several slightly different viruses. BA.1, the lineage that dominated early on, appears to be giving way to a sister lineage named BA.2 in Denmark and some other countries. That suggests BA.2 is a bit more transmissible, says virologist Tom Peacock of Imperial College London. Even if it is, “BA.2 is unlikely to cause a separate wave,” Peacock says, “but it may cause a ripple in the Omicron wave or slow down the decline in countries where the peak has passed.”

Delta might also make a comeback. That depends in part on how much more transmissible Omicron really is than Delta. It’s spreading so fast now because it can evade people’s existing immunity. But as immunity to Omicron builds up, that advantage will fade and the variants may compete on a more equal footing—if Omicron does not wipe out Delta before then. “If there is still some Delta circulating in September, then I think you can have coexistence,” says Trevor Bedford of the Fred Hutchinson Cancer Research Center. “And that would add to your burden of disease and add to complications in vaccination.”

The two variants might also recombine to produce a virus that incorporates both Omicron’s immune evasion tricks and Delta’s severity, says virologist Christian Drosten, also at Charité. “That would be worrying because it could lead to a difficult next winter.” Entirely new variants of concern are likely to appear as well, including ones that hit on new combinations of mutations that elude human immunity. “I think the virus still has a lot of tricks up its proverbial sleeve and we need to approach the future of the pandemic with more humility,” Titanji says.

The proliferation of animal reservoirs is also worrying, scientists say. One theory for the origin of Omicron is that SARS-CoV-2 infected some animal species, racked up a series of mutations, then popped back into the human population as a very different virus. Ferrets, lions, deer, and many other species have been infected with the coronavirus, and could provide such a springboard. Hong Kong culled more than 2000 hamsters earlier this month after 11 hamsters in a pet shop tested positive for SARS-CoV-2. (The animals fell under suspicion after a cluster of human cases was traced to a pet shop worker.)

One scenario in particular could put an end to the newfound optimism: the emergence of a variant able to evade not just human antibodies, but also the T cell response, which protects from severe disease and death. No variant so far has done that. “The likelihood of that happening, I believe, is quite slim,” Madhi says. But if it does happen, he says, “then we are really dealing with another pandemic.”