Yesterday’s post was optimistic. Today’s post is different.

Scientists are looking at three variables with the new variant — transmissibility, virulence, and immune-evasion. As long as Omicron isn’t strong in all three categories, it can be managed. If it’s virulent and immune-evasive but not very transmissible, it won’t spread much. If it’s transmissible and virulent but not very immune-evasive, vaccination will contain it. If it’s transmissible and immune-evasive but not very virulent, it’ll spread widely but won’t make people severely ill.

The earliest preliminary evidence from South Africa is that Omicron falls into the third category. Read yesterday’s post for encouraging news that people who are testing positive there are shaking the virus off, with most patients across several hospitals not even needing supplemental oxygen. If that’s how the variant operates globally — and in all age groups, importantly — then the coming global wave might not be a major killer.

But.

Evidence suggests that Omicron *is* immune-evasive to some unknown degree. And data keeps trickling in pointing to it being extremely transmissible, whether because it’s more contagious than Delta or more capable than Delta of infecting people with prior immunity (or some combination of both). The more contagious the variant is and the more easily it spreads among the previously immune, the less virulent we’ll need it to be if we hope to avert catastrophe. If it’s one-tenth as dangerous as Delta but infects 100 times as many people, it’ll send 10 times the number of people to the hospital that Delta did. We’d need it to be one one-hundredth as dangerous in my hypothetical to maintain the status quo.

Which means the worse the transmissibility and immune-evasion numbers look, the more likely it becomes that we’re going to get walloped even if Omicron is somewhat milder than Delta.

Virologist Trevor Bedford has been looking at the data in South Africa, trying to estimate the reproduction number for Omicron. He’s not prone to sky-is-falling hyperbole about COVID but he’s nervous about what he’s seeing. His best guess is that the variant has a reproduction number of 3 or 3.5, which would mean it’s infecting twice as many people as Delta and is comparable to how quickly COVID was spreading in the U.S. at the start of the pandemic before any mitigation measures were in place. In other words, after nearly two years of South Africa and the rest of the world acquiring a large degree of immunity against the coronavirus, Omicron somehow seems to be running as freely as the initial Wuhan strain was.

The size of this wave will depend largely on the susceptible population. Although current data cannot fully address this, I suspect there is decent immune evasion and some individuals protected from infection by Delta will be susceptible to Omicron. 19/19https://t.co/iGGAg51HCA

— Trevor Bedford (@trvrb) December 4, 2021

Bill Hanage is an epidemiologist at Harvard who’s also poring through the preliminary data, not just in South Africa but in the UK. The problem with using South Africa to gauge how Omicron will behave in the U.S. is that only a quarter of its population is vaccinated and Delta hadn’t been spreading there much recently. That makes it uncertain if Omicron is actually outcompeting Delta instead of just filling a vacuum. It’s possible that in western countries where Delta is prevalent and vaccination rates are high, like the UK, Omicron will get crowded out by Delta and won’t spread much. But what scientists are seeing in the UK numbers suggests that it is spreading rapidly there:

Omicron's rapid growth in the UK, with 68% of its population vaccinated, adds further concern beyond what we're seeing in South Africa https://t.co/YtGHhxEssA

— Eric Topol (@EricTopol) December 5, 2021

Hanage is forced to conclude that Omicron is outcompeting Delta, which means hospitals may soon be crushed with patients unless the new variant is drastically less virulent than the old one:

Yes, that is consistent with Omicron cutting into Delta’s turf, in a place Delta had made its own and where it was causing a lot of infections and also plenty of mostly mild breakthrough cases. It has an advantage 7/n

— Bill Hanage (@BillHanage) December 5, 2021

There’s still things we can do. Everything I know leads me to think vaxxed and boosted folks are in the best place to ride this out. And other stuff like masks will help control spikes. But I would be lying if I didn’t say I was seriously worried. I am seriously worried 15/end

— Bill Hanage (@BillHanage) December 5, 2021

What about the vaccines? Are they helping at all to contain the spread of the variant? Maybe. The Times reports on a doctor in Israel who picked up Omicron abroad and brought it back to his home country, where he spent three days interacting with friends, patients, and colleagues before testing positive. At last check, just one person he had contact with has been infected. It may be that the large number of boosters administered in Israel has restored most people’s immunity to the point where they’re capable of fending off the variant when they’re exposed, a hopeful sign. Although scientists believe that Omicron has some degree of immune-evasiveness because of all of the mutations on its spike protein, I haven’t seen one yet who thinks it’ll render the vaccines wholly ineffective.

But:

To Dr. Maor, who was still in isolation at home on Wednesday night, it was still concerning that he had been hit so hard by the virus, despite being fully vaccinated himself, and despite being a fit nonsmoker without any chronic medical conditions. The cardiologist spent Saturday and Sunday in bed with a fever, sore throat and aching muscles — and only began to feel considerably better on Wednesday afternoon.

“Despite everything, despite the vaccines and the booster, I was in bed for 48 hours,” Dr. Maor said in a phone interview. “If I didn’t have the vaccine, I probably would have ended up in the hospital.”

Maor is just 45 years old and in good health. If Omicron is capable of leaving him bedridden after three doses of the vaccine, how likely is it that the variant is so mild that the elderly, the immunocompromised, and those with comorbidities have nothing to fear from it?

Maybe the promising data yesterday about mild cases in South Africa has less to do with a dramatic decline in virulence of the variant and more to do with the fact that it’s mostly younger people who have tested positive so far. As it reaches older people, that picture might change:

If we switch to a log scale, we can better compare the growth rates:

On current trends, patients on oxy (mostly due to Covid) will soon pass Delta trajectory, and numbers in ICU are also heading up fast (obv be wary of extrapolating ICU trend, where data/reporting is bumpy) pic.twitter.com/NjG7Hx1XyY

— John Burn-Murdoch (@jburnmurdoch) December 4, 2021

Note too that the person in Israel whom Maor infected was himself vaccinated and boosted. The Minnesota man who seems to have caught Omicron at a convention in New York City was also triple-dosed. We already have hard proof, in other words, that boosters don’t render people immune to the variant. And if that’s true, what sort of jeopardy are people who’ve had two doses — or no doses — in? The Guardian notes today that more than half of the UK’s Omicron patients so far have been double jabbed. And 20 percent of the adult U.S. population hasn’t received a single shot of the vaccine, putting them in the same position most South Africans are in as cases there skyrocket. Maybe they’ll benefit from natural immunity they acquired previously. Maybe they won’t.

I’m going to go out on a limb and guess that within the next two weeks the scientific consensus will be that yes, the vaccines do need to be updated for Omicron and it needs to happen as quick as humanly possible. But there’s no guarantee that an updated vaccine will work. (See the end of yesterday’s post for more on that.) And even if it does, it’ll take three months at the earliest for the updated vaccine to be available to the public. Given the astonishing speed with which Omicron appears to spread, what are the odds that the variant will have already arrived, caused a massive wave, and begun to recede by the time the vaccines are ready?