Upsizing and restarts: Covid vaccine trials rumble on

The pause on enrolment into Astrazeneca’s pivotal Covid-19 vaccine study proved short-lived; the trial resumed in the UK six days after a safety concern halted proceedings. However, a substantial expansion of the Pfizer and Biontech trial, also announced over the weekend, shows that other developers are having to proceed carefully. Almost 50% more subjects will be sought as the partners seek to increase population diversity, in terms of age and underlying conditions, as well as adding to safety and efficacy data. Adequately reflecting target populations will be important as developers present findings to regulators and, ultimately, the public – Moderna has also been actively improving the representation of minority groups in its programme. Another potential motivation for the upsizing could be to improve the trial’s chances of showing a benefit, so this might not be an encouraging sign. Leerink analysts suspect the motivation is more likely to be regulatory and commercial – striving for a best-in-class breadth of label – and note that the new patients are unlikely to contribute to an interim read-out anyway, which remains on track for October. With Merck also entering the clinic last week, all of these developers will need to start thinking about differentiation.