Tony Reardon

I am sorry Jacob but the 90% efficacy figure does not mean that “... more than 90% of candidates given the vaccine did not produce symptoms of the virus” as you state. This is a misunderstanding. The trial consisted of 43,538 people split 50/50 into those who had the vaccine and a control group who did not (apparently this group received a meningococcal vaccination). The vaccine requires two doses and all but about 4,000 (total from both groups) received the second dose. The press release tells us that 94 people showed symptoms and these were split between the vaccinated group and those that received the placebo. If there was zero effect, one would expect the 94 would be split 50/50. What the 90% effective says is that the split was 10/90 so about 8 people in the vaccinated half and 86 in the control half showed symptoms. In the control group only about 0.5% showed symptoms which reduces to 0.05% in the vaccinated group so more than 99% of candidates in both groups showed no symptoms. Injecting about 20,000 people stopped about 78 cases.

Jacob Mitchell

Hi Tony, thanks for reading and your comment. Standing by our interpretation here which is the vaccine candidate was found to be more than 90% effective in preventing COVID-19 in participants without evidence of prior SARS-CoV-2. It appears your calculations and interpretation of the results assumes all participants in the study have been exposed to SARS-CoV-2 virus which is incorrect. Your approach may be more applicable if it were a challenge study where trial participants are intentionally exposed to live SARS-CoV-2 virus and then assessed for infection/protection by RT-PCR testing and/or presence of symptomatic COVID-19 disease. For Pfizer/BioNTech it is an event driven trial where not all participants will, or need to be, exposed to the SARS-CoV-2 virus. It was not designed to test all study participants for COVID-19 on a routine basis during the follow-up period. An event in this trial refers to a participant exhibiting pre-defined signs/symptoms of COVID infection which is then confirmed by RT-PCR testing (I've added a link below where you can see the full protocol description). This means a participant is only tested if presenting with symptoms. It’s also worth noting the >90% efficacy number reported by Pfizer/BioNTech is not set in stone and is likely to change as more events in the study accrue and the trial completes. Feel free to reach out via email if you want to discuss further. It's certainly an interesting topic at the moment. Jacob.