The best news has come from Moderna, the U.S. biotech giant. It is reported that two jabs, each with only one-quarter of the standard dose of its COVID-19 vaccine gave rise to long-lasting protective antibodies and virus-fighting T cells. The trials involved nearly three dozen people. The results point out the way where less is more and can benefit more people with limited quantity of the vaccine.

  Following the early trials, Moderna’s mRNA-based vaccine trials had shown that a 100-microgram dose would be the ideal one. But recent studies have shown that a half-dose seemed to be just as good as the standard dose at stimulating immune protection. In a trial which started six months after the second shot, nearly all of the 35 participants had ‘neutralizing’ antibodies as well as T cells, both ‘killer’ cells that can destroy infected cells and a variety of ‘helper’ cells that aid in general immune defence. The levels of....