CNN  — 

A new subvariant of Omicron is spreading rapidly in some parts of the world. This spinoff from the original Omicron variant, called BA.2, has been found in at least 49 countries, including the United States. In some countries, like Denmark, BA.2 has already surpassed the original Omicron (BA.1) as the dominant variant.

Because it doesn’t cause a certain signature on lab tests called an s-gene target failure, it can look like other coronavirus variants on a first screen. That has some calling it “the stealth variant.”

How worried should we about this “stealth” Omicron? Are vaccinated people still protected? What about those who recently had Covid-19—could they be reinfected? And can tests pick up this subvariant?

For answers to these and other questions, I spoke with CNN Medical Analyst Dr. Leana Wen. Wen is an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health. She is also the author of “Lifelines: A Doctor’s Journey in the Fight for Public Health.”

CNN: Should we be worried about this new Omicron subvariant?

Dr. Leana Wen: We should be cautious and monitor new information as it comes out, but we shouldn’t worry.

Here’s what we know about BA.2. Given how quickly it has spread and even displaced the very contagious original Omicron variant, known as BA.1, in some places, this new subvariant appears to have an even higher rate of growth. There’s no evidence that it causes more severe disease than the original Omicron, which has been associated with milder illness than previous variants like Delta.

Preliminary studies from the United Kingdom also show that people vaccinated and boosted are as well-protected against BA.2 as BA.1. That’s very important, because it means that those vaccinated and boosted are unlikely to become severely ill if infected with this new version of Omicron.

CNN: If you’re diagnosed with Covid-19, how would you know if you have the original Omicron variant versus this one?

Wen: Most people do not find out what variant they are infected with, because that takes special technology called sequencing that takes place in certain labs. Right now, the orig