A new subvariant of omicron, BA.2, is raising concern among public health experts. Here's what you need to know.

What is BA.2? BA.2 is a subvariant of omicron, the COVID-19 variant that caused a spike in new cases this winter. (NPR)

What's different about BA.2? Per NBC, BA.2 has 28 mutations in its spike protein, several of which are unique to it.

Is it more contagious than omicron? Yes: according to CNET, BA.2 is the most contagious subvariant of omicron.

Where has it been detected? BA.2 has become the most dominant strain in both South Africa and Denmark, per NPR.

What about the US? According to the CDC, BA.2 has been detected in several states, such as California, Texas and New York.

The CDC reported mid-Feb. that BA.2 was responsible for 3.2% of all new COVID-19 cases in the US. (CNET)

Does BA.2 cause severe illness? So far, little is known about the severity of the subvariant. (NBC)

Are vaccines effective against BA.2? Yes: per the CDC, vaccines protect most from hospitalization and death.