Mighty omicron has morphed into distinct subvariants — including “stealth omicron,” which might be even more infectious.

Omicron-specific vaccines are in the works, but may not offer any more protection than what we have now. And there has been talk of a fourth shot, at least for those who are most vulnerable to illness.

But before you erupt in a primal scream, take a deep breath: Experts say there’s no need to worry just yet.

“Not worried, but paying close attention,” said Dr. John Swartzberg, clinical professor emeritus of infectious diseases and vaccinology at UC Berkeley.

“Wait and see,” agreed Dr. Yvonne Maldonado, professor and chief of the division of pediatric infectious diseases at the Stanford University School of Medicine.

‘Stealth omicron’

The World Health Organization said this week that, while omicron still dominates globally, it’s monitoring several “sublineages.” There’s BA.1, BA.1.1 and BA.2, the “stealth omicron.”

At a global level, BA.2 has been increasing relative to BA.1 in recent weeks, even while the global circulation of all variants is declining, WHO said.

Registered nurse Hannah Fauni loads a syringe with the single-dose COVID-19 vaccine by Johnson & Johnson on March 11, 2021, in Moreno Valley. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

“(I)nitial data suggest that BA.2 appears inherently more transmissible than BA.1, which currently remains the most common omicron sublineage reported,” WHO said.

“This difference in transmissibility appears to be much smaller than, for example, the difference between BA.1 and Delta,” WHO said. And data on clinical severity from South Africa, the United Kingdom and Denmark, where immunity from vaccination or natural infection is high, found no difference in the severity of disease between BA.2 and BA.1.

Scientists are watching very closely.

“So far, BA.2 has been identified in at least 74 countries,” said Berkeley’s Swartzberg by email. “It currently comprises ~4% of isolates in the US, but it was 1.8% less than two weeks ago. It’s dominant, for example, in Denmark and India. The good news is that, despite BA.2 increasing in the US and UK, the number of cases continues to decrease.”

There are three things to consider when determining the level of concern, he said.

The first is transmissibility. “Between 30% and 50% more transmissible than BA.1 and BA.1.1. This is not good,” he said.

The second is its ability to evade the immune response. “Perhaps. Data is mixed.”

And the third is if it is more virulent. “Perhaps. Again, data is mixed.”

Dr. George Rutherford, professor of epidemiology and biostatistics at UC San Francisco, takes heart from a new study on the severity of “stealth omicron” compared to its predecessor in South Africa, which found that the odds of being admitted to the hospital did not differ.

“These data suggest that while BA.2 may have a competitive advantage over BA.1 in some settings, the clinical profile of illness remains similar,” the study concluded.

Dr. Elizabeth Hudson, regional chief of infectious diseases with Kaiser Permanente Southern California, is inclined to agree.

“It’s not clear … that BA.2 is any ‘worse’ than BA.1, nor does it appear that someone who has had BA.1 is likely to get infected with BA.2 afterwards,” she said by email. “It appears the COVID vaccines/boosters work well against it, too, which is also encouraging news and another reason to get vaccinated and boosted against this virus.

“It is important for all of us to monitor this subvariant closely, however, as the rate of it is increasing,” she said. “As to what may happen with it in the U.S., so far, the numbers, while increasing, have not shown the type of rapid increase we saw with BA.1. Over the next 2-3 weeks, we’ll know for sure if we’re going to see BA.2 become the predominant variant in the U.S. As with all things COVID-related, with more time comes more data that shows us which direction the pandemic is actually headed.”

Swartzberg made a prediction. “I’ll go out on the limb and say that I do not think BA.2 will represent a serious problem in the U.S.,” he said. “It may slow our recovery from the Omicron surge, but there is no evidence of even that to date.”

Omicron boosters?

Researchers are working on vaccines that specifically target omicron’s adaptations, raising the possibility of shots tailored to the latest strains, much like the current flu vaccine regimen.

Medical assistant Nancy Alfaro administers the Pfizer vaccine to 6-year-old Lia Suchey Castro Ronan at Clinton Elementary School in Compton on Nov. 5, 2021. (Photo by Chuck Bennett, Contributing Photographer)

Pfizer and BioNTech announced a clinical study to evaluate an omicron-based vaccine candidate in January. Moderna dosed its first participant in a clinical trial of an omicron-specific vaccine in January as well.

Animal studies, however, suggest that may be unnecessary.

“There is no substantial evidence that they will protect better than the current mRNA vaccines. And, even if they did, with Omicron decreasing so rapidly, the need is not currently there,” Swartzberg said.

If people are vaccinated and boosted, “they have the best protection possible against all the current variants,” Kaiser’s Hudson said. “In terms of future vaccination needs, much of this will depend on the direction COVID takes over the next 6-8 months. If no more variants of concern arise, it is likely those who are fully vaccinated and boosted will have a long-lasting protection against COVID. If we see any new variants, that could change the calculus here.”

There has been talk of a fourth shot, at least for those who are most vulnerable, but new studies suggest that the third dose of an mRNA vaccine like Pfizer’s or Moderna’s protects for a good, long time.

While omicron can evade antibodies — molecules that bind to the virus’ spike protein and stop it from infecting cells — a third shot of an mRNA vaccine prods the immune system to mount a much more robust response, studies have found.

“There is general agreement that humoral (antibody) immunity from the third jab wanes after four months,” Swartzberg said. “Still, the vaccine offers good protection against hospitalization and death. Some very good studies on memory B-cells and T-cells suggest we may have much longer protection against serious disease. … Tomorrow, I’ll be four months out from my third jab — I’ll not be running out and getting a fourth (and I’m well over 65).”

Kaiser’s Hudson agrees.

“The latest data indicates that those who are immunocompetent and are fully vaccinated and boosted likely do not need a fourth dose. The COVID vaccine works on different parts of our immune system and by doing so allows us to create a durable immunity. If no new variants arise, most people will have excellent protection after receipt of a booster, and will not need more for now,” she said.

Once COVID-19 becomes endemic — which is to say, transitions from a global health emergency to persistent background noise that must be managed — there’s a good chance people will need COVID-19 booster vaccines, perhaps on a yearly or every-other-year basis, Hudson said. But that remains to be seen.

“Ask me a year out from people’s third jab if we need an annual booster,” Swartzberg said. “Only time will allow us to answer this question.”

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