Big news from Pfizer, with apparent high efficacy (>90%) based on 94 confirmed COVID-19 cases at their interim analysis.

A thread on how I interpret this news. Briefly:
"Celebrate, but let the process play out over time as intended."
1/8
https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-vaccine-candidate-against

Vaccine trials are "event-driven." They continue until enough endpoints have accrued (here, lab-confirmed *symptomatic* infections). Statisticians can take planned "early looks" at the data, and so allow us to tell if a product is working exceptionally well (or not at all). 2/8

When the vaccine is highly effective, we need less data to see it. While trials are planned for 150+ total events, this is what we need for a 60% efficacy vaccine. I say this because 94 events is a lot of data for a vaccine trial, and even more so when efficacy exceeds 90%. 3/8

Pfizer's first analysis was planned for 32 events, which they pushed back after discussions with FDA. But by the time they analyzed the data, 94 had accrued. This shows how quickly trials can generate results when placed in hotspots (and how much transmission is ongoing!). 4/8

While the results are exciting, of course we will want to independently evaluate them. Unlike treatments, promising data from vaccines do not immediately change standard of care. The vaccines will undergo a rigorous review process first which will play out over time. 5/8

Things I will be most interested in seeing:
- How well does the vaccine prevent severe disease?
- How well does the vaccine prevent infection?
- How well does the vaccine work across different subgroups (e.g. the elderly)?
From @mlipsitch and me:
6/8 https://science.sciencemag.org/content/early/2020/10/21/science.abe5938

We also do not want to interfere with the conduct of other ongoing trials. Where Pfizer's product remains limited, placebo-controlled follow-up is critical. We will need many vaccines to meet demand, including vaccines that can be delivered to resource-limited settings. 7/8

But overall this is great news for Pfizer and for other vaccines in development, as they are targeting the same protein. And it is a testament to just how quickly this research is moving. 8/END https://twitter.com/nataliexdean/status/1310613702476017666?s=20