Large trials this summer and fall could provide the first evidence that some of the experimental COVID-19 vaccines are working. AstraZeneca, which is developing an adenoviral vector vaccine designed at the University of Oxford, is recruiting 10,000 people in the UK, 30,000 people in the US, and potentially 2,000 people in Brazil for its Phase III study to determine if the vaccine is effective. If the trial is successful, AstraZeneca says, it could start distributing the vaccine as early as September in the UK and October in the US.

Moderna plans to begin a 30,000-person Phase III study of its messenger RNA (mRNA) vaccine in July. The firm is working with the contract manufacturer Lonza to produce 500 million doses or more per year.

And J&J, which like AstraZeneca is developing an adenoviral vector vaccine, says it will begin its first clinical trial in the second half of July—two months earlier than anticipated. The trial will test the vaccine in 1,045 healthy volunteers in the US and Belgium. J&J is also trying to move faster on planning for its larger trials.