The foot race to develop the first effective vaccine against COVID-19 involves an awfully crowded field, with 137 candidate vaccines in pre-clinical study worldwide and another 23 actually in development. But a leader seemed to emerge today with research published in the Lancet reporting promising results in a robust study by investigators at Oxford University in England.

The study began in April, with a sample group of 1,077 adults aged 18 to 55—an age group young enough to tolerate exposure to SARS-CoV2, the virus that causes COVID-19, with less risk of adverse effects than would be seen in older, more vulnerable adults. The group was divided more or less in half, with 543 participants receiving the experimental COVID-19 vaccine, and the other 534 serving as a con…