Vaccination mandates at federal and local levels have resulted in a string of lawsuits. On Dec 16, a federal appeals court reinstated a Biden administration rule requiring private employers of 100 or more workers to impose companywide immunization. That ruling is expected to be appealed to the Supreme Court.

The move came a day after the administration asked the court to reinstate another mandate that applies to healthcare workers. A federal judge issued a preliminary injunction last month to halt that.

In Illinois, a group of teachers recently filed a class action lawsuit against school COVID-19 requirements for vaccines, face masks and testing. In some cities, police unions are opposing vaccine mandates through lawsuits, although experts said this was aimed at protecting officers and the public. A judge has temporarily blocked New York City's municipal workers' vaccine requirement for a police detective who doesn't want to be inoculated.

Since COVID-19 vaccines were introduced, 14 percent of people in the US said they would never get a shot. They claimed religious or health exemptions, cited mistrust of the government, or opposed "authoritarian controls".

Experts said people's attitudes toward vaccination reflect partisan divides, and the vaccines have widened this split.

At least six conservative broadcasters who questioned COVID-19 vaccines died from the virus this year, according to a National Public Radio, or NPR, report. Their deaths may mirror a wider trend in the US－people who live in parts of the country that support former president Donald Trump are less likely to be vaccinated and more likely to die from COVID-related complications, the report said.

The NPR analysis shows that counties that voted for Trump had almost three times the death rate of those that voted for Biden in last year's presidential election.