Early data from trials of three potential COVID-19 vaccines released on Monday, including a closely-watched candidate from Oxford University, increased confidence that a vaccine can train the immune system to recognize and fight the novel coronavirus without serious side effects.

Whether any of these efforts will result in a vaccine capable of protecting billions of people and ending the global pandemic that has claimed more than 600,000 lives is still far from clear. All will require much larger studies to prove they can safely prevent infection or serious disease.