Today Pfizer announced encouraging results of its SARS-CoV-2 vaccine co-developed with BioNTech. It demonstrates an efficacy above 90% at 7 days after the second dose is given, according to interim results from the companies’ phase 3 trial. The trial has enrolled roughly 44,000 volunteers, 39,000 of whom have received both doses. The final analysis will occur after 164 cases of COVID-19 have been confirmed. In the interim analysis, 94 cases have been diagnosed. The vaccine monitoring committee has not identified any serious safety concerns.

So what does this all mean?

The study originally began with Phase 1 and Phase 2 dosing, safety and efficacy trials before moving into its current Phase 3 or final study stage. Initially in Phase 1 there were two RNA vaccine candidates developed by BioNTech – one directed at the receptor binding protein of the novel coronavirus and the other directed at its well described “spike protein”. It is important to note that there has never been until now an RNA vaccine. The vaccine candidate selected for Phase 2/3 evaluation was the spike protein at a dose of 30 µg.

The candidate vaccine is a two shot series with each injection separated by 21 days. According to today’s press release,  the evaluable case count reached 94 and the case split between vaccinated individuals and those who received the placebo indicates a vaccine efficacy rate above 90%, at 7 days after the second dose – or 28 days from the first dose. They did not release the number of cases seen between the treatment and placebo group. Those numbers will be helpful to see as will the distribution of severity of disease. Ideally, one would hope that a vaccine would prevent severe cases of COVID-19.

While these results are certainly encouraging, distribution of the vaccine itself has a major obstacle – namely its super-cold storage requirements. The vaccine, which is based on a novel technology that uses synthetic mRNA to activate the immune system against the virus, needs to be kept at minus 70 degrees Celsius (-94 F) or below. This is an obstacle for even the most sophisticated hospitals in the United States (in fact Mayo Clinic does not have this capability) and therefore will significantly limit when and where it is available. California has already said it will not provide vaccine supplies to facilities without adequate cold-storage capabilities.