The rapid spread of the Omicron variant of COVID-19 worldwide "may have positive implications in terms of decreasing the Covid-19 burden of severe disease," according to a new study funded by the Gates Foundation and South African, U.S. and U.K. government agencies.
Led by researchers in South Africa, where the variant was first identified, it's the latest study to suggest the pandemic is approaching endemic status, calling into question the benefits of strict mitigation policies beyond high-risk groups.
The preprint, not yet peer-reviewed, found that the "neutralizing immunity" provided by Omicron infection extended to the Delta variant, which appears to be more "pathogenic" than Omicron and still comprises a substantial proportion of COVID infections in several countries.
It was based on 15 participants, mostly vaccinated, who were tested at a median of four days after symptom onset and again 14 days later. They showed 14.4-fold increased neutralization of subsequent Omicron infection but also 4.4-fold increased neutralization of Delta infection, as determined by antibody response.
Two of the original 15 were later excluded because they did not "detectably neutralize Omicron at either timepoint."
The results suggest Omicron infection "may result in decreased ability of Delta to re-infect those individuals," the researchers wrote. If the new variant is indeed less severe, "the infection may shift to become less disruptive to individuals and society."
Beyond South African institutions, the 30-odd researchers in the study are affiliated with Columbia University, the University of Washington and Imperial College London.
The enhanced immunity to Delta was "especially" strong for vaccinated participants, tweeted lead author Alex Sigal, who is affiliated with the Africa Health Research Institute, University of KwaZulu-Natal and Germany's Max Planck Institute for Infection Biology.
Commenters on his tweet thread debated whether it was a good idea to publish results based on such a small study population.
Exactly how Omicron compares to Delta is a matter of ongoing scientific debate.
Researchers affiliated with South Africa's National Institute for Communicable Diseases concluded that Omicron infections, which hit 98% of all COVID cases in that country in early December, were associated with a lower risk of hospitalization than Delta infections.
Omicron hospitalizations also had a reduced risk of "severe disease" compared to Delta hospitalizations, though the risk was similar between Omicron and non-Omicron hospitalizations in general. "Some of this reduction is likely a result of high population immunity," the preprint cautioned.
Another preprint by University of Edinburgh researchers, citing "early national data" from Scotland, concluded that "Omicron is associated with a two-thirds reduction" in hospitalization compared to Delta.
Only 15 hospitalizations were observed among nearly 24,000 Omicron infections. The study found that a booster shot adds "substantial" protection against symptomatic Omicron infection compared to at least 25 weeks after the second vaccine dose.
A recent Imperial College London study, however, cast doubt on Omicron's purported lower severity, citing admittedly "very limited" hospitalization data. It found the risk of reinfection with Omicron was 5.4 times greater than with Delta, and was also not peer-reviewed.
That study was led by Neil Ferguson, who has a 20-year history of vastly overestimating projected death tolls from infectious diseases. His early projections of COVID deaths were used to justify strict lockdown measures in the U.S. and U.K.
Omicron hasn't become dominant everywhere. The CDC ratcheted back its estimate of the variant's prevalence among new COVID cases for the week of Dec. 18 to less than a quarter, down from nearly three-quarters. That percentage had more than doubled by the week of Dec. 25, however.
Even as federal and state health officials urge vaccinations and boosters to protect people from the most serious cases of COVID, research suggests that low-risk groups will benefit equally from natural immunity, if not more so.
A peer-reviewed study in Nature Immunology, published last week, found important differences in how children respond to COVID, which is "generally mild or asymptomatic" for them, compared to adults. The findings could be useful for tailoring "pediatric vaccination regimens."
Not only do children have high antibody responses to the virus's spike protein, but spike-specific T cell responses "were more than twice as high in children and were also detected in many seronegative children, indicating pre-existing cross-reactive responses to seasonal coronaviruses."
Their antibody and cellular responses continued for six months, compared to "relative waning" in adults, and their spike-specific responses were "broadly stable beyond 12 months. Therefore, children generate robust, cross-reactive and sustained immune responses to SARS-CoV-2 with focused specificity for the spike protein."
An English-language report on a Norwegian study of 400 individuals, who were infected with COVID in the country's first wave last year or second wave this month, found only 6 percent were hospitalized and none had been reinfected.
More than half had "high" antibody levels 10 to 12 months after infection, and 94 percent had "good amounts" a year later, according to the ScienceNorway report. Anne Kristin Møller Fell, chief physician and project manager for the study, said the researchers were surprised how high antibody levels were for mild cases.