What are the differences between omicron and BA.2?
Dr. Huerta responds 4:14
(CNN) --
A new version of the omicron variant of the new coronavirus is spreading rapidly in some parts of the world.
This derivative of the original omicron variant, called BA.2, has been found in at least 49 nations, including the United States.
In some countries, such as Denmark, BA.2 has already overtaken the original version of omicron (BA.1) as the dominant variant.
Because it doesn't cause a certain signature in lab tests called s-gene target failure, it can look like other coronavirus variants at first glance.
For this reason, some call it "the stealth variant".
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How worried should we be about this "stealthy" omicron?
Are vaccinated people still protected?
What about those who recently had covid-19?
Could they get infected again?
Can tests detect this subvariant?
Should you expect an omicron-specific booster shot?
This is how a doctor responds
To get 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."
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Should we worry about this new subvariant of omicron?
Dr. Leana Wen: We should be cautious and monitor new information as it comes out, but we shouldn't worry.
This is what we know about BA.2.
Given how quickly it has spread and even displaced the highly contagious original omicron variant, known as BA.1, in some places, this new sub-variant seems to have an even higher rate of growth.
There is no evidence that it causes more severe disease than the original omicron, which has been associated with milder disease than earlier variants such as delta.
Preliminary studies from the UK also show that vaccinated and boosted people are as well protected against BA.2 as against BA.1.
That's very important, because it means that vaccinated and boosted people are unlikely to get seriously ill if they get infected with this new version of omicron.
If you are diagnosed with covid-19, how would you know if you have the original omicron variant versus this one?
Wen: Most people don't find out which variant they are infected with, because that requires a special technology called sequencing that is done in certain labs.
Right now, the original BA.1 omicron variant still accounts for over 99% of new infections in the US, so if you're diagnosed with covid-19, chances are this is the one you have.
If someone recently had omicron, could they be re-infected with the new variant?
Wen: It is unlikely.
Recent infection, especially in combination with previous vaccination, protects against reinfection.
We don't know how long that immune protection will last.
Given how similar BA.1 and BA.2 are to each other, it stands to reason that someone who just had covid-19, and therefore probably has BA.1, is not going to get BA.2 in the near future.
Will the new booster vaccine for omicron work against BA.2?
Wen: Pfizer and Moderna have announced that they are both testing vaccines against omicron.
Since both BA.1 and BA.2 are subvariants of omicron, it is expected that the vaccine is likely to be effective against both.
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However, until clinical trials are complete, we won't know how effective the new omicron-specific booster is, compared to the vaccine and the booster we've already been using.
No one should wait for a specific omicron booster if they are already eligible for a booster.
If you are five months since the second Pfizer or Moderna dose, or two months since the one-dose Johnson & Johnson vaccine, you should get a booster now.
What could happen if BA.2 becomes dominant in the US?
Wen: This is certainly a possibility, as has happened in other countries.
A more transmissible variant means that it displaces the previous variants.
At best, we have enough people protected here in the US due to vaccination and recent infection that BA.2 does not cause a substantial increase in cases.
We could continue down the path of experiencing a lull in case numbers through the spring and summer.
Another scenario is that BA.2 tempers the sharp drop in cases we're seeing, and we end up having a longer fourth wave than we would with BA.1 alone.
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In either situation, the key is to continue to monitor whether vaccination and boosters continue to protect against serious BA.1 and BA.2 disease.
If so, that means the vaccines are successful;
That's what vaccines were designed for, to keep us out of the hospital and to prevent serious illness and death.
Does stealth mean that the new subvariant is not detected in tests?
Wen: No, there is no evidence to suggest that BA.2 is not detectable with laboratory PCR or home antigen tests.
What is your advice to protect me and my family from this subvariant?
Wen: There are many people who want to continue to take precautions to avoid getting infected with covid-19: those who are immunosuppressed, for example, or others who are medically fragile and therefore still vulnerable to serious outcomes despite being vaccinated.
There are families with young children under the age of 5 who are not yet eligible for the vaccine, although it looks like that could come.
Another contagious virus means that people who want to avoid getting Covid-19 have to continue to take precautions.
The most important is the use of a mask indoors, and the quality of the mask really matters.
The best mask is one that fits well and is comfortable, can be worn constantly, and is N95, KN95, or KF94 certified.
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Wear these masks any time you are indoors around people whose vaccination status is unknown.
When coronavirus infection numbers are high in your community, you may want to take extra precautions, such as asking everyone outside your household to take a rapid test before meeting you indoors.
Will this be the last variant we see?
Wen: Almost certainly not.
New variants appear all the time, because that's what viruses do: they mutate when they replicate.
Whether a new variant causes global concern depends on whether it is more contagious, more virulent, or can override previous immunity.
This is why real-time surveillance is so important, and why vaccination is key.
The more population immunity we have, the less viruses will spread and mutate, and the faster we can all get out of this pandemic.
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