WILMINGTON, Del. (NewsNation Now) — In one of his first moves as president-elect, Joe Biden outlined his coronavirus response plan and announced a 13-member task force to deal with the pandemic.

Biden and Vice President-elect Kamala Harris received a briefing from the newly formed advisory board on Monday morning. Biden then delivered an address on the pandemic, warning that the United States is “still facing a very dark winter.”

Biden highlighted the importance of mask-wearing, saying another 200,000 lives could be lost before a vaccine is widely available to Americans.

“A mask remains the most potent weapon against the virus,” Biden said.

The president-elect also emphasized that he would be guided by science in laying out plans to fight the virus.

The address comes after Biden announced a coronavirus working group tasked with developing a blueprint for containing the disease, once he takes office in January.

The Transition COVID-19 Advisory Board will be led by three co-chairs, former Surgeon General Vivek Murthy, former Food and Drug Administration Commissioner David Kessler, and public health expert Dr. Marcella Nunez-Smith of Yale University.

Dr. Beth Cameron and Dr. Rebecca Katz are serving as advisors to the transition on COVID-19, and will work closely with the advisory board.

“Dealing with the coronavirus pandemic is one of the most important battles our administration will face, and I will be informed by science and by experts,” said Biden in a statement. “The advisory board will help shape my approach to managing the surge in reported infections; ensuring vaccines are safe, effective, and distributed efficiently, equitably, and free; and protecting at-risk populations.”

Vice President Mike Pence is scheduled to lead a meeting with the Trump administration’s White House Coronavirus Task Force Monday. The meeting was scheduled to be closed to the press.

The briefings come as Pfizer announced progress in its vaccine trial, with early data signaling it may be 90% effective at preventing the virus.

The company, which developed the vaccine with the German drugmaker BioNTech, said it is on track to file an emergency use application with U.S. regulators later this month.

Biden and President Donald Trump commented on the news.

Trump took to Twitter to applaud the vaccine development progress, as well as the stock market boost that it brought.

“STOCK MARKET UP BIG, VACCINE COMING SOON. REPORT 90% EFFECTIVE. SUCH GREAT NEWS!” he wrote.

Biden congratulated the “brilliant women and men who helped produce this breakthrough,” but he also warned that there’s still a long road ahead.

“America is still losing over 1,000 people a day from COVID-19, and that number is rising — and will continue to get worse unless we make progress on masking and other immediate actions,” Biden said. “That is the reality for now, and for the next few months. Today’s announcement promises the chance to change that next year, but the tasks before us now remain the same.”

More than 237,000 Americans have died since the start of the coronavirus pandemic. The United States saw a record number of new infections last week, with the total number of cases nearing 10 million, according to John Hopkins University.

After four days of uncertainty as votes were counted in key states, Biden’s victory in Pennsylvania Saturday put him over the threshold of 270 Electoral College votes he needed to clinch the presidency. Trump has not conceded and has vowed to challenge the outcome in court.

The coronavirus task force announcement kicks off a busy week for Biden and Harris as they move forward with the presidential transition.

On Sunday, the president-elect’s transition team launched a new website, BuildBackBetter.com, and a new social media handle, @transition46, to provide the public with information on the handover.