Vaccine Odyssey

 Recently, Pfizer announced that their COVID-19 afforded >90 protection in their phase III clinical trial. Today, Moderna reported results that suggest 95% protection for their vaccine, also in phase III trials.

Both vaccines use SARS-CoV-2 spike protein mRNA. One potentially significant difference is that the Pfizer vaccine requires storage at -70C, while the Moderna vaccine only requires storage at -20C, the temperature of a typical household freezer. This distinction could become significant when it comes to vaccine distribution, since -70C freezers are currently more rare and expensive, and dry ice, which can substitute for shipping purposes and temporary storage, is apparently hard to get these days. Of course, a serious crash vaccination program would fund freezers and dry ice, and there are plenty of vendors that can meet the demand.

Neither the Pfizer nor the Moderna trial are challenge trials. The study design in each case calls for subjects in both arms to acquire natural COVID-19 infections in order to measure efficacy. A perverse benefit of the skyrocketing infection rates  is that vaccines in phase III during the winter should easily reach the numbers of infected subjects they need.