Omicron updates: More transmissible, immune evading, but still not cause for panic

COVID-19 cases are rising rapidly in countries where Omicron is spreading, including South Africa, the U.K., and Denmark. Chart from Our World in Data, retrieved September 12.

We continue to learn more about this new variant as it spreads rapidly across the world, though much of the data are still preliminary. Here are a few major updates:

  • Omicron is still spreading very quickly in South Africa, as well as in the U.K. and Denmark—two other countries with great genetic surveillance. Preliminary estimates based on data from these countries suggest that the variant’s R-value is between 3 and 4, indicating that the average person infected with Omicron infects three or four others. As Sarah Zhang put it in The Atlantic: “Omicron is spreading in highly immune populations as quickly as the original virus did in populations with no immunity at all.”
  • Early vaccine studies show a drop in antibody levels against Omicron, but that doesn’t necessarily correspond to overall protection. This week, we saw the first results from early studies evaluating how well vaccines work against Omicron. Here’s a summary, drawing from Katherine Wu’s coverage of these studies in The Atlantic: vaccinated people confronted with Omicron appear to produce a lot fewer antibodies that can fight the virus, compared with older variants. Numbers range from a five-fold drop in antibodies to a 41-fold drop. But remember, antibodies are just one part of the immune system—specifically, they’re the part that’s easiest to measure. Vaccinated people also have memory immune cells that provide protection over a long time period, which isn’t captured in antibody studies. We’ll need more time and more data to actually evaluate how vaccines fare against Omicron in the real world, rather than in the lab.
  • The vaccines seem to protect against severe disease and death from Omicron. So far, the data suggest that our existing COVID-19 vaccines still work quite well at protecting people from severe symptoms—even when those severe symptoms are caused by an Omicron case. “When the shots’ protection ebbs, it tends to do so stepwise: first, against infection, then transmission and symptoms, and finally against severe disease,” Wu writes. For vaccinated people to lose protection against severe disease, the virus would have to change much more than Omicron has. At the same time, however, some experts are concerned that non-mRNA vaccines may not fare as well against Omicron as Moderna and Pfizer, conferring a disadvantage to the low- and middle-income countries that have had less access to the mRNA vaccines.
  • Booster shots increase protection against Omicron. While vaccinated people are less protected against infection with Omicron than previous variants, booster shots appear to help close that gap—even though currently-available booster shots are not designed specifically for Omicron. One U.K. study suggests that boosters can increase vaccine effectiveness against infection from 30% to 75%, for people who received the Pfizer vaccines. In other words: Omicron is a good reason to go get your booster shot, if you’re eligible and you live in a place where the shots are available.
  • Experts continue to be skeptical about Omicron being “more mild.” Reports out of South Africa continue to suggest that cases caused by Omicron are more mild than cases caused by Delta, with doctors saying that fewer patients are requiring hospitalization and those hospital stays are shorter than previous outbreaks. But many of the South Africans getting sick with Omicron may have some protection from vaccination or past infection; this means they’re more likely to have mild cases, as biostatistician Natalie Dean explains in an excellent Twitter thread. Plus, even if Omicron is more mild, it appears to be more transmissible—and a smaller share of severe cases out of a larger pool of cases overall can still lead to a pretty big number of people going to the hospital. In addition, we have zero data at this point on how Omicron may impact Long COVID cases, or how well vaccines protect against Long COVID from an Omicron infection.
  • Early U.K. data confirm Omicron’s high contagiousness and its capacity for evading protection from vaccines and prior cases. After the U.K.’s best-in-the-world genetic surveillance agency first identified Omicron in late November, I wrote that the country would likely provide invaluable data on this variant. Less than two weeks later, the U.K. Health Security Agency has released its first Omicron report. The country’s real-world data confirm that Omicron can spread quite fast: for example, “19% of Omicron cases resulted in household outbreaks vs 8.5% of Delta cases,” wrote epidemiologist Meaghan Kall in a summary of the report. The report also “paints a very consistent picture for Omicron being immune evading,” Kall said, though booster shots help a lot.
  • Anime NYC was a likely Omicron superspreader event. More and more reports have emerged of Omicron cases connected to Anime NYC, a convention held in Manhattan in mid-November. The CDC is currently investigating the convention: officials are working with the NYC health department to contact all 53,000 convention attendees for testing and contact tracing. “Data from this investigation will likely provide some of the earliest looks in this country on the transmissibility of the variant,” CDC Director Dr. Rochelle Walensky said at a press briefing on Tuesday.
  • The CDC formally named Omicron a Variant of Concern. On Friday, the CDC officially designated Omicron as a Variant of Concern and added it to the variant tracking page of the agency’s COVID-19 dashboard. As of December 4, Omicron is causing 0.0% of new COVID-19 cases in the U.S., the CDC estimates. The variant has yet to be added to the CDC’s state-by-state data. Given the continued geographic disparities of the U.S.’s genomic surveillance system, however, we may expect that the variant is already spreading in states where it has yet to be formally identified.
  • Omicron can likely compete with Delta, but we need more data to get a better sense of how well. “Omicron is picking up speed in Europe, which has often served as a preview of what was headed the U.S.’s way. It’s an early sign that the already bleak situation here may get worse,” writes Andrew Joseph in a recent STAT News story. U.K. data suggest that Omicron could cause a majority of cases there within two to four weeks, Joseph reports, and the U.S. may not be far behind. Still, more real-world data from countries and regions with clear Omicron outbreaks will give us a better idea of just how worried we need to be about a potential Omicron-fueled surge.

In summary:

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