Stealth Omicron Can’t Hide Its Lethality

A subvariant of Omicron, dubbed “stealth Omicron” is “substantially” more transmissible than the original variant and poses a greater threat to vaccinated and booster-upped individuals, according to a study by Danish investigators that has not yet been peer reviewed. The original Omicron is BA.1; the stealth Omicron is BA.2.

“We conclude that Omicron BA.2 is inherently substantially more transmissible than BA.1, and that it also possesses immune-evasive properties that further reduce the protective effect of vaccination against infection, but do not increase its transmissibility from vaccinated individuals with breakthrough infections,” states the study, which was published on medRxiv website.

Investigators with the University of Copenhagen analyzed data taken from 8541 Danish households between December 20, 2021, and January 11, 2022. They found that individuals infected by stealth Omicron were 33% more likely to infect others, compared to original Omicron.

The study’s lead author Frederik Plesner Lyngse, PhD, told Reuters that “if you have been exposed to Omicron BA.2 in your household, you have 39% probability of being infected within seven days. If you instead had been exposed to BA.1, the probability is 29%.”

Lyngse said in a recent Tweet: “What is [Omicron] BA.2 and why do we care? Omicron BA.2 is genetically very different from BA.1. They differ by approximately 40 mutations.” He added that Morten Rasmussen, PhD, a researcher at Stanford University, “has told me told that BA.2 differs more from BA.1 genetically than [the Alfa variant of COVID-19] differs from the original Wuhan strain!”

Stealth Omicron has also been detected in the United States, Norway, the United Kingdom, and Sweden, but not to the extent that it’s been detected in Denmark where, as of the second week in January, it accounted for 82% of new COVID-19 cases.

Individuals who’ve been vaccinated and those vaccinated who’ve also gotten a booster are less likely to become infected by either Omicron or stealth Omicron, the study states.

“We found BA.2 to be associated with an increased susceptibility of infection for unvaccinated individuals (Odds Ratio (OR) 2.19; 95%-CI 1.58-3.04), fully vaccinated individuals (OR 2.45; 95%-CI 1.77-3.40) and booster-vaccinated individuals (OR 2.99; 95%-CI 2.11-4.24), compared to BA.1,” the study states. “We also found an increased transmissibility from unvaccinated primary cases in BA.2 households when compared to BA.1 households, with an OR of 2.62 (95%-CI 1.96-3.52).”

Omicron was first noticed in South Africa. Tulio de Oliveira, PhD, who directs South Africa's Centre for Epidemic Response and Innovation, said in a recent Tweet that while infections from stealth Omicron increase in that country, but against a “background of decreasing infections” COVID-19 infections overall.

Eric Topol, MD, founder and director of the Scripps Research Translational Institute, said in a recent Tweet that the study’s findings suggest that three doses of a vaccine offers good protection against “symptomatic infection,” but added that stealth Omicron’s “increased transmissibility will prolong the Omicron wave in many places.”