The U.K. health secretary said at least 10 people were in hospital with the variant, which experts believe may cause a milder form of Covid-19 but can evade immunity and spread rapidly.
The seven states have all seen an increased seven-day average of cases since the beginning of December, though not all have reached their record levels from last fall and winter.
Early lab data released Wednesday suggests a booster shot of the Pfizer-BioNTech vaccine is necessary to ensure protection against omicron, rather than just two doses.