As Covid Vaccine Nears, There Are Reasons for Hope and Caution

Thousands of researchers in more than 30 countries have been collaborating and competing this year on more than 200 projects to develop a vaccine against the novel coronavirus in record time. In the most encouraging scientific advances so far, two vaccines have delivered positive news that their shots were more than 90% effective in late-stage trials. However, a number of hurdles still need to be cleared, and testing that was halted on other promising candidates highlighted the uncertainties and