January 19, 2022

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Omicron is now the dominant U.S. COVID variant. Is it as contagious as measles? – San Francisco Chronicle

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With startling speed, the immensely contagious omicron variant of the coronavirus has become the dominant strain in the U.S.

In some places, such as New York, the prevalence of omicron is at over 90%, federal authorities said. Its prevalence is unclear in California, which has not updated its variant sequencing numbers since last Wednesday, when the state tallied just 49 omicron cases — a number that by now is certain to be vastly higher.

“I’ve NEVER seen anything like the speed of Omicron,”Dr. Tom Frieden, a former CDC director under President Barack Obama, tweeted Monday night. “It’s as infectious as measles spreading in a non-immune population, with a much shorter incubation time therefore much faster doubling time.”

President Biden will address the nation on Tuesday about the threat posed by the variant.

Dr. Jorge Salinas, a Stanford infectious disease expert, said omicron “couldn’t catch us at a worse moment” nationally, with pandemic fatigue high and Christmas just days away.

He said he’d advise most people cancel their holiday plans, or severely curtail them.

“I understand it’s Christmas in five days, but the virus doesn’t care if it’s Christmas or not,” he said, noting that among the big risks facing the Bay Area is that large numbers of people who perform critical functions — like cardiac surgeons — could become sick at the same time.

Coronavirus cases in the Bay Area have been rising, but they have not yet reached the astronomical level of New York and London. According to state data, there were 26,127 cases reported in California on Sunday, a significant increase from 19,047 reported on Dec. 12. (Those figures generally reflect the numbers that span three days, rather than from a single day.) The Bay Area recorded 4,112 cases on Dec. 19 compared with 2,516 one week earlier. San Francisco saw 796 cases reported on Dec. 19, versus 316 on Dec. 12.

Dr. John Swartzberg, an infectious disease expert at UC Berkeley, said omicron was not quite as contagious as measles, but certainly more catchy than chicken pox.

Dr. Peter Chin-Hong, an infectious disease expert at UCSF, said there are “many parallels” between measles and more recent COVID-19 variants. Respiratory droplets from measles patients can remain airborne for up to two hours, he noted — which means a person can become infected by lingering virus in a room even if the initial person is no longer there.

“Whether or not omicron can be as adept as measles in unbelievable transmissibility remains to be seen,” he wrote in an email. “Omicron is likely aerosolized the same way measles is — small droplets are created that can linger in the air like dandelions — and it will certainly give measles the toughest competition of any SARS CoV2 variant to date.”

Contra Costa County officials said Monday that three omicron cases have been identified there, and that the variant has likely been circulating in the community for weeks. San Francisco said on Friday that it had 30 probable but unconfirmed omicron cases, in addition to the confirmed, first-in-the-country case shortly after Thanksgiving. But the extraordinary speed of omicron — which was first detected in the U.S. less than a month ago — means that numbers from a few days ago are virtually meaningless.

The reproductive number known as R0, pronounced “R naught,” measures a disease’s transmissibility at the beginning of a pandemic with no preexisting immunity, said Warner Greene, a virologist and senior investigator at the Gladstone Institutes in San Francisco. It represents how many people one sick person will infect.

According to a study released in October, the original COVID-19 strain that emerged from Wuhan has an R0 value of 2.79. The delta variant has a value of between 5 to 6 — about twice as contagious as the original strain.

Chicken pox has an R0 value of 9-10. The R0 value of measles is estimated at 12 to 18.

Coronavirus Resources

COVID-19 Map: Data on trends in the Bay Area and across California

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Greene said to really know the true R0 value of omicron, more information is needed. He cited an estimate from Martin Hibberd, a professor of emerging infectious diseases at the London School Of Hygiene & Tropical Medicine, that omicron could have an R0 of 10.

Chin-Hong said “a lot more fully vaccinated people will get breakthrough infections, but will not likely get very ill and are very unlikely to die.”

For unvaccinated people, the situation is much more serious.

“It will be very difficult to avoid getting infected with omicron,” Swartzberg said. “You may have been lucky with the other variants and the ancestral strain. It’s unlikely you will be with omicron. The unvaccinated will be the biggest spreaders of omicron and they will be the ones most likely hospitalized from it.”

The Bay Area, despite its relatively high vaccination rates, will soon feel omicron’s force.

“Widespread infections will take many people out of work and school, government services, restaurants and businesses could close temporarily as infected staff will be isolating at home, and anxiety will be rampant,” Chin-Hong said. “Because health care workers will be among those with breakthrough infections, hospital capacity could be at risk.”

Salinas echoed these concerns. “Our actions today, tomorrow, this holiday, during the next 10 days or so, will affect how this outbreak looks in January,” he said. “I think that the outlook is quite problematic, for all of America, including the Bay Area. Many people feel the Bay Area will be spared, and I wouldn’t bank on it. I would take action as if we were going to see what New York is seeing now.”

Some experts believe that omicron may result in milder disease — perhaps because so many people have immunity from vaccines or prior infections — but the sheer numbers of likely infections, plus the impact on health care workers, could still result in hospitals being swamped.

Even before omicron, hospitalizations were ticking up in California: On Sunday there were 3,523 people hospitalized with COVID-19 statewide compared with 3,268 a month ago, and the Bay Area had 336 COVID-19 patients hospitalized on Dec. 19 versus 291 on Nov. 19.

Chin-Hong is confident that “deaths will most certainly remain low” in the Bay Area, but less vaccinated areas will see a significant increase in hospitalizations and deaths.

“In the best-case scenario, it will be a fast upswing of infections and a quick decline as community immunity quickly increases,” he said.

Experts stress the importance of getting boosted if you are eligible. Swartzberg said to double mask or wear a well-fitted surgical mask in most indoor settings, and to do away with cloth masks.

“Being vaccinated and boosted is the best shot that we have against omicron, but it is not enough,” he said.

Chronicle staff writer Erin Allday contributed to this report.

Kellie Hwang is a San Francisco Chronicle staff writer. Email: kellie.hwang@sfchronicle.com Twitter: @KellieHwang

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