British health authorities reported 41,385 new COVID-19 cases Monday, the highest daily rise since the pandemic began. Over the last seven days, 256,220 people tested positive, which is a 25.7% increase in positive tests since the week prior.

England's Chief Scientific Adviser Patrick Vallance said last week that the newly identified U.K. variant is more dominant and significantly more transmissible than the old coronavirus variant.

There’s no evidence the new variants are more deadly and it’s highly likely the vaccine will still work, experts said at a virtual Q&A hosted by the World Health Organization last week.

In total, the U.K. has reported 2,329,730 infections and 71,109 deaths from the virus.

-ABC News' Christine Theodorou contributed to this report.

One out of 17 Americans, a total of 19 million people, have tested positive for coronavirus, according to data from Johns Hopkins University. One in 1,000 have died from the virus.

Since some states don't report and others give incomplete updates over the holidays, last week's data doesn't provide an up-to-date picture of the U.S. outbreak. But even without those numbers, December's forecast remains grim, according to an ABC News analysis of data from The COVID Tracking Project.

Since Dec. 1, there has not been a single day with less than 1,000 COVID-19 related deaths reported, the data showed.

The United States logged more than 5.4 million COVID-19 cases in December, more than any month on record and roughly equivalent to 70 Americans testing positive for the virus every 30 seconds.

-ABC News' Arielle Mitropoulos contributed to this report.

New Jersey vaccinated its first nursing home resident, a 103-year-old resident of Roosevelt Care Center in Old Bridge Monday.

Mildred Clements, a Newark native who has lived through two pandemics, was met by a round of applause from the governor and state health commissioner after receiving her shot. Residents and staff at roughly 90 long-term care facilities in New Jersey are slated to start vaccinations Monday, according to the governor's office.

-ABC News' Aaron Katersky contributed to this report.

The Transportation Security Administration (TSA) on Sunday saw the highest number of people screened at the airport since the pandemic hit, a spokesperson tweeted Monday.

The 1,284,599 people screened at airports nationwide marks the sixth day in the last 10 with more than 1 million airline screenings. "If you choose to travel, please wear a mask," Lisa Farbstein, the TSA spokesperson, wrote on Twitter.

-ABC News' Michael Kreisel contributed to this report.

Public Health England does not recommend mixing COVID-19 vaccines from different suppliers, according to the agency's head of immunizations, Dr. Mary Ramsay.

"We do not recommend mixing the COVID-19 vaccines -- if your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa," Ramsay said in a statement Saturday. "There may be extremely rare occasions where the same vaccine is not available, or where it is not known what vaccine the patient received. Every effort should be made to give them the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all."

The clarification comes amid questions over the British government's updated guidance on COVID-19 vaccines, which now says that if individuals who received the first shot go to an immunization site where that same vaccine is not available for a second shot, or if the first vaccine received is unknown, "it is reasonable to offer one dose of the locally available product to complete the schedule."

"This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again," the guidance adds.

The guidance, which was updated Thursday, also notes that "there is no evidence on the interchangeability of the COVID-19 vaccines although studies are underway," and thus "every effort should be made to determine which vaccine the individual received and to complete with the same vaccine."

Next week, the United Kingdom is set to begin distribution of a COVID-19 vaccine developed by England's University of Oxford and manufactured by British-Swedish pharmaceutical giant AstraZeneca, after the drug was approved Wednesday for emergency supply. Another COVID-19 vaccine developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech was approved in the U.K. on Dec. 2 and rollout began a week later.

ABC News' Zoe Magee contributed to this report.