Why Making a Covid Vaccine Is Only the First Hurdle

In the quest to develop vaccines against Covid-19, researchers have overcome challenges that typically require years, if not decades, to beat. After the first experimental shots produced positive results in late-stage trials -- a huge feat in itself -- drug companies and health officials faced another set of obstacles as they prepared to inoculate hundreds of millions of people around the world. A number of uncertainties remain, including how long any vaccine’s protection against the coronavirus will last. Answering those questions will help tell us how much longer face masks, social distancing, mass testing and contact tracing will be needed to fight the pandemic. Among the hurdles ahead:

The U.K. on Dec. 2 became the first Western country to authorize a Covid shot, using fast-track options regulators have laid out. Scientists hope it will be the start of a series of vaccines to be authorized, produced and distributed. The U.K. cleared a vaccine from Pfizer Inc. and BioNTech SE that was about 95% effective in preliminary analyses of trial results announced in November. In the same month, a second vaccine candidate from Moderna Inc. more or less matched that result, and a third, from AstraZeneca Plc, was 70% effective on average. Months earlier, China and Russia had begun inoculating selected groups, such as medical workers and military personnel, with domestically developed vaccines before they had undergone full testing.