(NewsNation Now) — As the omicron variant continues to be detected worldwide, this is not the first time a coronavirus variant has raised alarm bells in the global health community.

But how often do these alarm bells turn into something with global health implications? Here’s what you need to know.

Twenty-seven COVID-19 variants have been tracked by the World Health Organization, but only five of those have been of major concern.

Alpha, beta, delta, gamma, and omicron are the five variants of concern as described by the WHO. A variant of concern means that the variant either has increased transmissibility, increased severity, and/or significant impacts to global health.

So far, the delta variant seemingly has been the only variant to overwhelm global health care systems. In June, delta supplanted other variants as the most dominant strain.

WHO also monitors variants of interest. The WHO’s variants of interest — currently lamba and mu — have been determined to exhibit “genetic changes that are predicted or known to affect virus characteristics,” including transmissibility, immune escape, disease severity or resistance to treatment. If there are changes to the virus that means it looks like it has the potential to do more harm, then it is designated as a variant of concern.

Multiple mutations have been downgraded because they didn’t end up impacting global health systems despite being more transmissible or causing more severe infections.

Variants like epsilon which emerged in the U.S. as significantly transmissible was seen in a few global cases and wasn’t directly linked to more severe illness. Epsilon has now been downgraded to a “formerly monitored variant.”

One of the things that has caused this concern over omicron is it’s seemingly more transmissible. But still so much is unknown about the variant.