Ever since the COVID-19 pandemic unfurled across the United Kingdom, hematologist John Willan has worried about the disease’s toll on his patients. In March 2020, Willan, who works at the University of Oxford and Wexham Park Hospital, began to track the hospital’s COVID-19 cases among people with leukemias, lymphomas, and other blood diseases. He counted not just the dozens of deaths, but also persistent and disabling symptoms collectively called Long Covid, which have plagued millions over the past 3 years.
These days, Willan is less anxious. After Omicron began spreading in late 2021, COVID-19 deaths became a rarity even among his frail and immunocompromised patients, he says. And infections now carry a lower threat of lingering complications. “These patients with Omicron, they’re much less likely to get Long Covid,” says Willan, whose patients are overwhelmingly vaccinated. Earlier this month, he reported in the British Journal of Haematology that his patients’ risk of Long Covid symptoms 3 months after infection had dropped from 46% with the original coronavirus strain and another called Alpha, to 35% with the Delta variant, to 14% with Omicron.
“My patients were so terrified … when COVID came out,” and rightfully so, Willan says. Although the number with protracted symptoms is still higher than he’d like, “I want to try and get a message to those people to say, ‘This is the actual risk to you now.’”
The trend appears in both vulnerable and healthy people. A group in the United Kingdom, Spain, and Italy reported this month in The Lancet Oncology that the risk of Long Covid among cancer patients fell from about 17% in 2021 to 6% more recently, as cases shifted to Omicron. Another just-published study of healthy Swiss hospital workers describes a similar pattern.
“The risk of Long Covid is not comparable between these variants,” says Philipp Kohler, an infectious disease specialist at St. Gallen Cantonal Hospital, who co-led the Swiss study. Vaccination, Omicron’s tendency to cause milder disease, and its distinct biology may all play a role, though the degree to which different factors blunt risk is a mystery.
Claire Steves, a geriatrician and epidemiologist at King’s College London, was the first to rigorously compare Long Covid rates after Omicron versus after Delta, which struck in mid-2021. She drew on data from the U.K. COVID Symptom Study, in which tens of thousands type information into an app. Data from 97,000 vaccinated people revealed a 4.5% risk of symptoms persisting 4 weeks after an Omicron infection versus 10.8% following a Delta infection, the group reported in The Lancet in June 2022.
Since then, several studies have shown a decline in risk, although they disagree about the absolute numbers. The definition of Long Covid is still in flux, study designs differ, and the frequency with which Long Covid symptoms such as brain fog and intense fatigue also strike uninfected people isn’t known, making it tougher to glean the prevalence of Long Covid today.
In the Swiss study this month in Clinical Infectious Diseases, Kohler and his colleagues, including infectious disease specialists Carol Strahm and Christian Kahlert, both also at St. Gallen, tried to pin down Long Covid risks in a cohort of Swiss health care workers. The team sorted participants—mostly female and young or middle-aged—by the variant they were likely infected with, based on the timing of their illness. Other volunteers, without a positive COVID-19 test and without antibodies to the virus, were assigned to a never-infected control group.
A survey given in June 2022 asked about Long Covid symptoms. “We decided this is not a yes or no question,” Kohler says, so among nearly 3000 respondents, the team counted how many of 18 typical Long Covid symptoms—such as headache, cough, joint pain, and brain fog—they had. Because many people in the general population have at least some of those symptoms, the team compared their frequency across different groups, including controls.
In the Omicron cohort, the average number of chronic symptoms was 0.52—below the other variants, but a touch above the control group’s 0.39. Although this suggests Omicron infection carries a chance of Long Covid, it pales compared with the original strain: The health care workers infected early on were still averaging more than one ongoing symptom, despite having been hit far earlier. They also continued to report more missed days from work than those who caught Omicron.
In some ways, these numbers aren’t surprising. During acute illness, Omicron is much less likely to land patients in the hospital due to severe disease, which researchers know is a major risk factor for Long Covid. But Steves says her data show lowered Long Covid risk “is not just about severity.” Her group analyzed data on only nonhospitalized individuals and found the same gap. “I think it’s highly likely that [Omicron] is acting as a different virus,” she says.
Steves’s study “suggests there may be an intrinsic property of Omicron that reduces the conversion to Long Covid,” says Akiko Iwasaki, an immunologist at Yale School of Medicine. Iwasaki and Steves speculate that how different viral variants infiltrate the body could be key. Earlier variants seem to spread to vital organs more often than Omicron does. Such spread might not always produce symptoms in acute infection, Iwasaki theorizes, but it might make someone more likely to wind up with Long Covid.
Though shifting variants are likely driving down Long Covid risk, vaccination is probably playing a role, too, although untangling its potency can be tricky. In Kohler’s study, outcomes after Omicron didn’t appear affected by vaccination, but other studies see a link.
Scientists also wonder how reinfections might fuel Long Covid cases. Kohler’s group has preliminary data suggesting that a person infected by the original COVID-19 strain and then by Omicron didn’t have a higher risk of Long Covid than those infected only by the original strains. Daniel Ayoubkhani, a principal statistician at the Office for National Statistics who analyzes Long Covid data, notes that the U.K. COVID-19 Infection Survey reported last month that 2.4% of participants described ongoing symptoms after a second infection versus 4% after a first; most of the infections were likely Omicron.
Still, Iwasaki notes that even a small risk of Long Covid means a lot of affected people. Given how disabling the syndrome can be, she hasn’t stopped worrying about the public—and herself. “I definitely don’t want to get the virus,” she says.
Ever since the COVID-19 pandemic unfurled across the United Kingdom, hematologist John Willan has worried about the disease’s toll on his patients. In March 2020, Willan, who works at the University of Oxford and Wexham Park Hospital, began to track the hospital’s COVID-19 cases among people with leukemias, lymphomas, and other blood diseases. He counted not just the dozens of deaths, but also persistent and disabling symptoms collectively called Long Covid, which have plagued millions over the past 3 years.
These days, Willan is less anxious. After Omicron began spreading in late 2021, COVID-19 deaths became a rarity even among his frail and immunocompromised patients, he says. And infections now carry a lower threat of lingering complications. “These patients with Omicron, they’re much less likely to get Long Covid,” says Willan, whose patients are overwhelmingly vaccinated. Earlier this month, he reported in the British Journal of Haematology that his patients’ risk of Long Covid symptoms 3 months after infection had dropped from 46% with the original coronavirus strain and another called Alpha, to 35% with the Delta variant, to 14% with Omicron.
“My patients were so terrified … when COVID came out,” and rightfully so, Willan says. Although the number with protracted symptoms is still higher than he’d like, “I want to try and get a message to those people to say, ‘This is the actual risk to you now.’”
The trend appears in both vulnerable and healthy people. A group in the United Kingdom, Spain, and Italy reported this month in The Lancet Oncology that the risk of Long Covid among cancer patients fell from about 17% in 2021 to 6% more recently, as cases shifted to Omicron. Another just-published study of healthy Swiss hospital workers describes a similar pattern.
“The risk of Long Covid is not comparable between these variants,” says Philipp Kohler, an infectious disease specialist at St. Gallen Cantonal Hospital, who co-led the Swiss study. Vaccination, Omicron’s tendency to cause milder disease, and its distinct biology may all play a role, though the degree to which different factors blunt risk is a mystery.
Claire Steves, a geriatrician and epidemiologist at King’s College London, was the first to rigorously compare Long Covid rates after Omicron versus after Delta, which struck in mid-2021. She drew on data from the U.K. COVID Symptom Study, in which tens of thousands type information into an app. Data from 97,000 vaccinated people revealed a 4.5% risk of symptoms persisting 4 weeks after an Omicron infection versus 10.8% following a Delta infection, the group reported in The Lancet in June 2022.
Since then, several studies have shown a decline in risk, although they disagree about the absolute numbers. The definition of Long Covid is still in flux, study designs differ, and the frequency with which Long Covid symptoms such as brain fog and intense fatigue also strike uninfected people isn’t known, making it tougher to glean the prevalence of Long Covid today.
In the Swiss study this month in Clinical Infectious Diseases, Kohler and his colleagues, including infectious disease specialists Carol Strahm and Christian Kahlert, both also at St. Gallen, tried to pin down Long Covid risks in a cohort of Swiss health care workers. The team sorted participants—mostly female and young or middle-aged—by the variant they were likely infected with, based on the timing of their illness. Other volunteers, without a positive COVID-19 test and without antibodies to the virus, were assigned to a never-infected control group.
A survey given in June 2022 asked about Long Covid symptoms. “We decided this is not a yes or no question,” Kohler says, so among nearly 3000 respondents, the team counted how many of 18 typical Long Covid symptoms—such as headache, cough, joint pain, and brain fog—they had. Because many people in the general population have at least some of those symptoms, the team compared their frequency across different groups, including controls.
In the Omicron cohort, the average number of chronic symptoms was 0.52—below the other variants, but a touch above the control group’s 0.39. Although this suggests Omicron infection carries a chance of Long Covid, it pales compared with the original strain: The health care workers infected early on were still averaging more than one ongoing symptom, despite having been hit far earlier. They also continued to report more missed days from work than those who caught Omicron.
In some ways, these numbers aren’t surprising. During acute illness, Omicron is much less likely to land patients in the hospital due to severe disease, which researchers know is a major risk factor for Long Covid. But Steves says her data show lowered Long Covid risk “is not just about severity.” Her group analyzed data on only nonhospitalized individuals and found the same gap. “I think it’s highly likely that [Omicron] is acting as a different virus,” she says.
Steves’s study “suggests there may be an intrinsic property of Omicron that reduces the conversion to Long Covid,” says Akiko Iwasaki, an immunologist at Yale School of Medicine. Iwasaki and Steves speculate that how different viral variants infiltrate the body could be key. Earlier variants seem to spread to vital organs more often than Omicron does. Such spread might not always produce symptoms in acute infection, Iwasaki theorizes, but it might make someone more likely to wind up with Long Covid.
Though shifting variants are likely driving down Long Covid risk, vaccination is probably playing a role, too, although untangling its potency can be tricky. In Kohler’s study, outcomes after Omicron didn’t appear affected by vaccination, but other studies see a link.
Scientists also wonder how reinfections might fuel Long Covid cases. Kohler’s group has preliminary data suggesting that a person infected by the original COVID-19 strain and then by Omicron didn’t have a higher risk of Long Covid than those infected only by the original strains. Daniel Ayoubkhani, a principal statistician at the Office for National Statistics who analyzes Long Covid data, notes that the U.K. COVID-19 Infection Survey reported last month that 2.4% of participants described ongoing symptoms after a second infection versus 4% after a first; most of the infections were likely Omicron.
Still, Iwasaki notes that even a small risk of Long Covid means a lot of affected people. Given how disabling the syndrome can be, she hasn’t stopped worrying about the public—and herself. “I definitely don’t want to get the virus,” she says.