Vaccines > Variants
As of the CDC's interpretive summary for September 17, after experiencing a brief decline in COVID-19 cases, the United States was once again seeing an increase in cases in most of the country.
This recent increase follows a previous summer surge that was fueled by the highly contagious Delta (B.1.617.2) variant and low vaccination coverage in many communities. COVID-19 vaccines offer strong protection against serious illness and death. High vaccination coverage is proven to reduce the spread of the virus. The less a virus spreads, the less opportunity there is for new variants to emerge.
The virus that causes COVID-19 constantly changes, or mutates, producing new variants of the virus. The Delta variant continues to be the predominant strain in the United States, making up more than 99% of cases.
On August 30, 2021, the World Health Organization classified the Mu (B.1.621) variant as a Variant of Interest (VOI). CDC has not designated Mu as a VOI at this time. The Mu variant reached a peak in the United States in late June 2021 and has steadily declined since then.* CDC continues to study and monitor all known variants and will continue to provide information when variants change classification in the United States.
Getting vaccinated is the best way to protect yourself, your family, and your community. It is also the best way to prevent new variants from emerging. A recent CDC study found that people who were not fully vaccinated had about 10 times the risk of being hospitalized with or dying from COVID-19 compared with people who were fully vaccinated. CDC recommends that everyone in the United States 12 years and older get vaccinated as soon as possible. To find a vaccine provider near you, visit Vaccines.gov or your state or local public health department website.
*At its peak, Mu made up less than 5% of all variants circulating in the United States. As of the CDC September 17 reporting summary, Mu made up less than 1% of all COVID-19 cases in the United States.