Due to the new variant of COVID-19 in the United Kingdom, Centers for Disease Control and Prevention (CDC) has issued an Order effective December 28, 2020. It requires all air passengers arriving to the US from the UK to get tested no more than 3 days before their flight departs and to provide proof of the negative result to the airline before boarding the flight. For more information on this testing requirement, see the CDC link here: https://wwwnc.cdc.gov/travel/notices/covid-4/coronavirus-united-kingdom