The UK approved a Covid-19 vaccine before the US. Here’s why.

An advisory committee to the US Food and Drug Administration on Tuesday released a briefing document detailing data on Pfizer and BioNTech’s Covid-19 vaccine candidate, which will be considered this week for emergency use authorization in the United States.

The document confirms that the vaccine’s efficacy against Covid-19 was 95%, occurring at least seven days after the second dose – an efficacy that had been previously reported by Pfizer. The proposed dosing regimen for the vaccine is to administer two 30-microgram doses 21 days apart.

However, the document also notes that the vaccine, called BNT162b2, appears to provide “some protection” against Covid-19 following just one dose.

The document describes the efficacy of Pfizer’s vaccine in the time between the first and second dose as 52.4%, but the document notes that “the efficacy observed after Dose 1 and before Dose 2, from a post-hoc analysis, cannot support a conclusion on the efficacy of a single dose of the vaccine, because the time of observation is limited by the fact that most of the participants received a second dose after three weeks.”

In other words, “the trial did not have a single-dose arm to make an adequate comparison.”

The document goes on to detail the safety profile of the vaccine as “favorable” and notes that the most common adverse reactions to the vaccine have been reactions at the injection site, fatigue, headache, muscle pain, chills, joint pain and fever.

Severe adverse reactions occurred in less than 4.6% of participants, were more frequent after the second dose and were generally less frequent in older adults as compared to younger participants, according to the document. The document adds that swollen lymph nodes also may be related to vaccination.

A total of six participants died during the trials, and “all deaths represent events that occur in the general population of the age groups where they occurred, at a similar rate.”

The document will be discussed in a meeting on Thursday, where the FDA’s Vaccine and Related Biological Products Advisory Committee will provide recommendations to the FDA on whether the vaccine is effective in preventing Covid-19 in people 16 and older and whether the potential benefits of the vaccine outweigh the risks.

“The committee will also discuss what additional studies should be conducted by the vaccine manufacturer following issuance of the EUA to gather further data on the safety and effectiveness of this vaccine,” according to the document.