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Omicron: What you need to know about the COVID variant

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  • Coronavirus
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With the Omicron variant of the coronavirus now dominant across the U.S., federal health officials are pleading with adults to wear masks and get a booster shot in hopes of curbing a feared surge in hospitalizations. 

The Centers for Disease Control and Prevention estimated Omicron made up 95% of circulating SARS-CoV-2 nationwide by January 4 — skyrocketing from around 3% in early December.

Early data suggests a booster shot is needed to restore protection against infection from Omicron, though the initial vaccine regimen still helps reduce the risk of severe illness and hospitalization. People who survived a prior case of COVID-19 appear to be at risk of reinfection from Omicron.

How well will the vaccines work against Omicron?

Two doses of the current Pfizer or Moderna vaccines appear to offer "considerable protection" against severe disease from the Omicron variant, Dr. Anthony Fauci said at a briefing on December 15, citing data from South Africa. And a growing body of preliminary laboratory studies testing people's antibodies against the variant found a sufficient boost of protection in those who received a third Pfizer or Moderna shot. 

"Our booster vaccine regimens work against Omicron," Fauci said. "And so the message remains clear: If you are unvaccinated, get vaccinated. And particularly in the arena of Omicron, if you are fully vaccinated, get your booster shot."

Drugmakers say they are still working to assess the impact of the new variant on their vaccines. Moderna, Johnson & Johnson, and Pfizer and BioNTech all say they are ramping up development of potential new versions of their vaccines in case changes are needed to respond to Omicron's mutations in the future. 

But so far, early findings from real-world studies and laboratory experiments suggest that the vaccine booster shots right now do not need to be changed, Fauci said.

Changing the strain targeted by the shots could benefit countries that are still vaccinating large swaths of their populations, and are months away from booster shots. 

Some vaccinated Americans might need additional booster shots to increase their protection. One study from NIH-backed scientists in Massachusetts suggested that recipients of Johnson & Johnson's vaccine who received a single booster "may benefit from additional mRNA vaccine doses" to broaden their protection.

Abroad, some health authorities are also considering shortening the interval for booster shot eligibility down to as little as three months after vaccination. The CDC recently updated its booster recommendations to say people who got the Pfizer-BioNTech or Moderna vaccines only need to wait five months, instead of six, before getting a booster.

How dangerous is the new variant?

Early data from South Africa suggested that patients face a lower risk of hospitalization from Omicron, though it was initially unclear if that's because the variant is milder than earlier waves or because more people have some immunity from prior infections. 

The first cases seen in the U.S. were largely in younger vaccinated travelers, who may be healthier than the general population, the CDC cautioned on December 10.

Dr. Fauci, the president's chief medical adviser, said on December 7 that figures from South Africa on hospitalizations appeared promising, but he and other experts have pointed to factors that could distort comparisons to prior waves: cases tend to be younger and may have widespread immunity from vaccines or from surviving a prior infection.

In South Africa, which reported an unprecedented surge of infections driven by the variant, officials saw a "sharp increase" of cases in hospitalized younger children not seen in previous waves.

Health authorities around the world are warning that the sheer number of cases resulting from the rapid spread of Omicron could be enough to overwhelm the health care system on top of a Delta variant surge that has already strained hospitals.

"Omicron is spreading at a rate we have not seen with any previous variant. We're concerned that people are dismissing Omicron as mild. Surely we have learned by now that we underestimate this virus at our peril," Dr. Tedros Adhanom Ghebreyesus, the head of the World Health Organization, told reporters on December 14.

Symptoms may be less severe, but Omicron can still be deadly

Doctors studying Omicron's spread around the world have found evidence suggesting that in many patients, the variant leads to less-severe symptoms that mostly affect the upper respiratory system — the nose, mouth and throat. That may help explain why it appears to pose a smaller individual risk of hospitalization or severe disease than earlier strains of the virus, which often invaded the lungs.

Research from South Africa's largest health insurer found that a sore throat ranked among the most common early Omicron symptoms, as well as congestion, a dry cough and lower back pain. Analysis of data compiled from reports of positive cases in London listed the top five symptoms as runny nose, headache, fatigue, sneezing, and sore throat. 

On December 20, health officials in Texas reported the first known U.S. death linked to Omicron. The man was in his 50s, unvaccinated, had underlying health conditions, and had previously survived a case of COVID-19.

The full number of U.S. COVID-19 deaths caused by Omicron is uncertain since not every case is sequenced by laboratories to determine what variant caused their infection.

While health officials have sounded optimistic that Omicron might lead to a smaller proportion of deaths than in previous waves, as has been seen in South Africa, the variant's steep transmissibility suggests the sheer number of cases could still lead to many more deaths.

"Even if the proportion of infections associated with severe outcomes is lower than with previous variants, given the likely increase in number of infections, the absolute numbers of people with severe outcomes could be substantial," the CDC's forecasters warned on December 21.

Will current medicines still work?

Spokespeople for Merck and Pfizer both say they believe their antiviral pills, which have been hailed as potential game-changers in the fight against the virus, will likely remain effective against Omicron. Pfizer's drug, Paxlovid, and Merck's, molnupiravir, were both granted FDA emergency use authorization in December.

Of the monoclonal antibody treatments currently authorized for COVID-19, only two drugs — one made by AstraZeneca and one from GlaxoSmithKline and Vir Biotechnology — appear to remain effective against Omicron. 

The Biden administration recently lifted curbs on the distribution of monoclonal antibodies from Regeneron and Eli Lilly, pointing to "significant variability" in Omicron's prevalence around the country and new guidelines published by the National Institutes of Health on prioritizing limited supplies of the drugs.

Regeneron said on December 16 it was working on "next generation" monoclonal antibodies that could effectively treat Omicron cases, acknowledging that its current antibodies "have diminished potency against Omicron."

Where did Omicron come from?

The sample of the first announced Omicron case was detected in South Africa on November 22. It has since been identified by the country's health authorities in samples there dating back to November 8, the CDC said

Several other countries have since announced finding cases dating back to before Omicron's public emergence in late November. 

The earliest case reported to GISAID, a global database tracking SARS-CoV-2's evolution, from laboratories in the United States dates back to a sample from Maryland dated November 21. On December 10, CDC said the earliest U.S. case discovered so far had symptoms on November 15 "in a person with a history of international travel." 

Omicron appears to have evolved separately from the Delta variant, descending from another strain that appeared in mid-2020. Some scientists speculate it may have accumulated so many changes while evolving for months in animals or an immunocompromised person.

"The Omicron variant is the most divergent variant that has been detected in significant numbers during the pandemic so far which raises serious concerns that it may be associated with significant reduction in vaccine effectiveness and increased risk for reinfections," European health officials said on November 26.

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