On Monday morning, the FDA published briefing documents for an upcoming meeting of a panel of independent medical experts who will weigh in on data from the most closely watched vaccine study in the agency's history. This offered the public its first unfiltered look at the clinical trial results that Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) submitted to support their request for emergency use authorization (EUA) for their coronavirus vaccine candidate, BNT162b2, and the biggest reveal so far is a positive one.

A single-dose of BNT162b2 appears effective

You may remember that BNT162b2 leaped over the 50% efficacy bar set by the FDA. Volunteers were shown to be 94.8% less likely to test positive for COVID-19 seven days or longer after receiving their second dose of the vaccine candidate.

According to the briefing document, a total of 121 volunteers tested positive for COVID-19 during the three-week period between their first and second injections. Since 82 of those cases occurred among volunteers randomized to receive a placebo, we can say BNT162b2 is 52.4% effective at preventing COVID-19 following the first dose, with some caveats.

IMAGE SOURCE: GETTY IMAGES.

It's important to remember that there wasn't a separate group of patients given just one dose; the vast majority of volunteers received their second injections as planned. Given that, we can't be confident a single dose of BNT162b2 will remain at least 50% effective for more than a few weeks.

This week's reveal won't change plans to distribute BNT162b2 in a two-dose regimen, but it's still terrific news from a public health perspective. The problem of people missing their booster shots has long been a pain point for public health officials.