Omicron scrambles what we know about immunity

The new variant is widely different than delta, and its origin remains a mystery

Published : 16 Dec 2021 09:19 PM

Forget the debate over how scared we should be of omicron. What matters is putting our energy into solutions that work — taking action that matters on a personal level and demanding effective actions from world leaders.

Scientists are already scrambling to learn how well our existing vaccines will work against this new coronavirus variant. That can help predict how much benefit might come from speeding up worldwide vaccination and booster campaigns and whether vaccine passports will protect people or give a false sense of reassurance.

Reports that most omicron cases are mild are understandably reassuring for many individuals — especially those of us who aren’t elderly or immunocompromised and have access to booster shots. But some scientists have frowned on such optimism because of the larger picture.

If this thing keeps growing exponentially and infects millions of people in a short time, health systems will collapse, even if a tinier fraction of cases are serious. Cases are rising rapidly in the U.K. and South Africa, suggesting that omicron has some advantage over delta, the currently dominant coronavirus variant. It might be that it’s inherently more transmissible, or that it’s better able to get past immunity in those who’ve been infected or vaccinated, or some combination of those factors. Omicron’s genes are weirdly different from previous variants, appearing to be only distantly related to delta. No one is sure where it came from — possibly from growing for months in immune-compromised patients, or from leaping into an animal host and back into humans.

It has 21 mutations in the top part of the spike protein, molecular epidemiologist Emma Hodcroft of the University of Bern said in an interview. Some of these mutations are alarming because they’d been observed in earlier variants that were good at evading immunity from vaccines or past infections.

In just a couple of weeks, scientists have accumulated an impressive amount of preliminary data. Some labs assembled mock versions of omicron by genetically manipulating other variants to carry some of the variant’s key mutations, Hodcroft said. Researchers can grow these “pseudo viruses” in petri dishes and test how well they stand up to antibodies extracted from the blood of vaccinated or previously infected people.

Then last week, a lab in South Africa made headlines with results on the behavior of actual samples of omicron. It found the virus did somewhat evade immunity generated by two shots of the Pfizer vaccine, but was neutralized well by antibodies taken from patients who had been both vaccinated and previously infected with earlier variants. At around the same time, Pfizer announced that antibodies from a booster shot helped stop omicron in laboratory experiments, though the findings aren’t peer reviewed, and outside researchers didn’t get to see the data.

At a press briefing Wednesday, Harvard infectious disease specialist Yonatan Grad said they still don’t know details of any of these experiments. Did the blood come from people who were vaccinated last month or 10 months ago? This matters because other studies demonstrated that antibodies from the Pfizer and Moderna vaccines wane significantly over six to nine months.

“In real humans, it might be more complex, but I think we can probably say that we expect more reinfection or breakthrough infections with omicron than we’ve seen with other variants,” Hodcroft said.

How severe those infections will be isn’t clear. Vaccines (or past infection) leave people with immune cells that hide in the bone marrow and lymph nodes, and these become activated if there’s a new infection and create a bunch of new antibodies. Lab experiments wouldn’t necessarily capture this phenomenon.

With only partial knowledge about the dangers of omicron, wealthy countries such as the U.S. are starting to push harder to get third doses into everyone, though we’d save more lives by getting initial doses to countries with low supplies. Scientists will know a lot more in three or four weeks, when cases of severe disease would be expected to crop up, after omicron has spread and cases have had time to progress, and epidemiologists can measure how fast the variant is expanding outside South Africa.

How and where the disease spreads will depend on past cases in the population, vaccine uptake, seasonal cycles and other factors nobody yet understands. The past behavior has been surprising.

Earlier variants, including alpha, rose fast in the eastern U.S. in the fall of 2020 and then plummeted in the middle of the winter 2021. Those early variants barely touched India, but delta suddenly exploded there in the spring of 2021. That wave, too, crested and fell suddenly.

With omicron, the severity of disease is going to be particularly hard to ascertain without waiting until it infects a sizable number of people of different ages. The original version of SARS-CoV-2 was mild in most people — and it was enormously destructive.

“Even if Omicron has a milder severity — and we don’t know this at the moment — if it spreads really quickly, even a smaller percent of a big number is a big number,” Hodcroft said. “We’re also, in most of the West, fairly ill-prepared for this, since our delta cases are riding so high — we have very little wiggle room left.”

So the best-case scenario would be either that omicron isn’t as transmissible as it first appeared and it fizzles out, or that it’s only little more transmissible than delta and a lot milder — so mild that almost nobody has to be admitted to an ICU.

“It would be the best thing we can hope for,” Hodcroft said, but it’s not something she or other experts are betting on.

Hope is fine as long as it doesn’t lull people into inaction or lessen the sense of urgency. A lot can be done now, including producing omicron-specific vaccines and doing a better job of distributing existing vaccines to the countries that need them most. People need to be ready for more restrictions if the worst-case scenarios play out.

There’s some evidence that vaccinations cut back on transmission. That means the more shots we can get into arms around the world, the fewer chances the virus has to stumble on some new variant — perhaps something that’s not mild at all.

Faye Flam is a Bloomberg Opinion columnist and host of the podcast Follow the Science. 

Source: Bloomberg