Columbia University

Dr. Anthony Fauci expressed "cautious optimism" Friday about the initial results from a coronavirus vaccine trial — which were widely celebrated this week — and said it remains "conceivable" that a vaccine for the deadly pathogen could be available by the end of the year.

Updated at 12:10 p.m. ET

The U.S. could have prevented roughly 36,000 deaths from COVID-19 if broad social distancing measures had been put in place just one week earlier in March, according to an analysis from Columbia University.

Underlining the importance of aggressively responding to the coronavirus, the study found the U.S. could have avoided at least 700,000 fewer infections if actions that began on March 15 had actually started on March 8.