BBC:
US scientists want more data before they will be confident they can reopen the economy without the virus flaring right back up again.
They want to know how many people are infected. They want to know more about whether people who’ve been infected are then immune and if so for how long.
…
The longer the country is shut down the more the economy suffers but also the fewer people are infected. That’s good for protecting the health system but health experts point out that there’s some conflict because it doesn’t allow people to develop immunity in large enough numbers to reach so-called herd immunity.