Coronavirus updates: Herd immunity by fall 'ambitious,' says surgeon general nominee

In England, those who attend house gatherings with more than 15 people -- in violation of lockdown rules -- will face hefty fines beginning next week, British Interior Minister Priti Patel announced Thursday.

First-time offenders face a fine of 800 pounds (around $1,097). The fine will double for each repeat offense to a maximum of 6,400 pounds (around $8,779).

More police officers are on dedicated patrols "taking targeted action against those small few who are letting everybody down,” said Martin Hewitt, chair of the U.K. National Police Chiefs' Council.

When asked by reporters Thursday whether England's lockdown is likely to end by the spring or summer, British Prime Minister Boris Johnson said it is "too early to say."ABC News’ Christine Theodorou contributed to this report.

Dr. Anthony Fauci, chief medical adviser to U.S. President Joe Biden, said received his second dose of the COVID-19 vaccine on Tuesday.

Speaking to reporters at the White House on Thursday afternoon, Fauci said he "felt under the weather for about a day" but now feels fine.

ABC News’ Ben Gittleson contributed to this report.

United Airlines, which reported a $7.1 billion net loss for 2020 in an earnings call Thursday, said it expected to have voluntary COVID-19 testing available at all of its hubs by February.

The airline said it is also working with local governments to classify its employees as essential workers for vaccinations, "both for their safety and the safety of [its] customers."

The carrier said it expects 2021 capacity to be down at least 51% versus the first quarter of 2019.

United said following vaccine distribution, business demand will take 18 to 24 months to recover. 

Executives said they expect the "inflection point" in travel recovery to occur in the second half of 2021, but it could happen sooner depending on the pace of vaccine distribution. 

ABC News’ Amanda Maile contributed to this report.

American pharmaceutical firm Eli Lilly and Company released new data showing that a laboratory-made protein delivered by infusion may help prevent COVID-19 infections at nursing homes. 

A phase 3 trial found that nursing home residents who got the monoclonal antibody drug were 80% less likely to develop symptomatic COVID-19 compared to nursing home residents who got a placebo infusion. 

Among all the study participants (including residents and staff), those who got the drug were 57% less likely to develop symptomatic COVID-19.

The Eli Lilly drug, called bamlanivimab, has FDA emergency authorization to treat people already sick with COVID-19 who might need to be hospitalized. The company says it will work with regulators to potentially expand this authorization to include nursing home residents and staff to help prevent outbreaks.

The U.S. Centers for Disease Control and Prevention advises that those who’ve had monoclonal antibody treatment wait 90 days until getting a COVID-19 vaccine.

ABC News’ Sony Salzman and Dr. Mishal Reja contributed to this report.