Another week, another set of preliminary results from a Covid-19 vaccine trial. This time it is the Moderna vaccine candidate, mRNA-1273. And, to judge by the figures put out by the company this morning, it has outdone the Pfizer vaccine in its efficacy. Out of the 30,000 people involved in the phase three trial (half of whom were given the vaccine and half of whom were given a placebo), 95 went on to contract Covid-19.