WASHINGTON — President Joe Biden opened his first formal news conference Thursday with a nod toward the improving picture on battling the coronavirus, doubling his original goal by pledging that the nation will administer 200 million doses of COVID-19 vaccines by the end of his first 100 days in office.

The administration had met Biden’s initial goal of 100 million doses earlier this month — before even his 60th day in office — as the president pushes to defeat a pandemic that has killed more than 545,000 Americans and devastated the nation’s economy.

But while Biden had held off on holding his first news conference so he could use it to celebrate progress against the pandemic and passage of a giant COVID-19 relief package, he was certain to be pressed at the question-and-answer session about all sorts of other challenges that have cropped up along the way.

A pair of mass shootings, rising international tensions, early signs of intraparty divisions and increasing numbers of migrants crossing the southern border are all confronting a West Wing known for its message discipline. Biden had been the first chief executive in four decades to reach this point in his term without holding a formal news conference,

While seemingly ambitious, Biden’s vaccine goal amounts to a continuation of the existing pace of vaccinations through the end of next month. The U.S. is now averaging about 2.5 million doses per day. An even greater rate is possible. Over the next month, two of the bottlenecks to getting Americans vaccinated are set to be lifted as the U.S. supply of vaccines is on track to increase and states lift eligibility requirements to get shots.

The scene looked very different from what Americans are used to seeing for formal presidential news conferences.