Government

For months, scientists and public health experts have been saying the most crucial part of defusing the Covid-19 pandemic will be developing a safe and effective vaccine. So it was cause for celebration this week when Pfizer announced that an early analysis showed its vaccine candidate was more than 90 percent effective.

Now the drug maker, the government and the public health community face a new challenge: quickly making millions of doses of the vaccine and getting them to the hospitals, clinics and pharmacies where they will be injected, two separate times, into people’s arms.