Buzz
Pfizer and BioNTech shared today that their vaccine candidate shows a promising 90% effectiveness in preventing COVID-19 in participants of their trial. While this is a positive sign, much more needs to be done before we have a fully functional and accessible vaccine.
Which vaccine is being discussed here?
Pfizer’s vaccine is one of four being tested in the U.S. Two of the candidates, including Pfizer’s, use mRNA technology rather than proteins or entire viruses. This is an innovative approach that has never been approved for a vaccine before.
This vaccine needs to be stored at ultra-low temperatures instead of regular refrigerators or freezers. While this creates logistical challenges, solutions like shipping the vaccine in specialized coolers may help resolve the issue.
The vaccine requires two doses, spaced three weeks apart.
What we know at this point
These results come from a Phase 3 trial, the final stage of testing before a vaccine could potentially be approved or granted emergency use authorization. The trial is ongoing, and these are preliminary findings.
The results have not been peer-reviewed, and even Pfizer’s own researchers do not have access to the complete data. (An independent review board shared the partial results with them; this separation ensures the integrity of the trial and prevents any bias or changes in interpretation.)
In their announcement and during discussions with reporters, Pfizer shared the following information:
94 participants in the trial contracted COVID-19, mostly from the control group.
The vaccine appears to be 90% effective.
The trial will proceed until a total of 164 cases have been reported.
They might have enough data to apply for emergency use authorization later in November.
According to earlier studies, side effects of the vaccine appear to include fever, chills, and body aches. STAT reports that these side effects are expected to resemble those of other adult vaccines, but possibly stronger than what we typically experience with a flu shot.
What is still unknown
It remains uncertain whether the vaccine will maintain its 90% effectiveness by the trial's conclusion. If it does, or stays close, it would be an exceptional outcome. Regulators have been targeting a threshold of 50%.
We don't yet fully understand how effective the vaccine is at preventing severe COVID-19 cases, though it appears to reduce the likelihood of contracting the virus in general. While it’s likely that a vaccine preventing cases will also reduce the severity of those cases, like the flu shot, we won't know for sure until more data is available.
It's still unclear whether the vaccine prevents infections specifically, as opposed to just cases. If you contract the coronavirus, you have an infection and could transmit it even without symptoms. A vaccine that stops infections would halt the spread, but one that only prevents infections from progressing to disease might not significantly impact transmission, only limiting its severity.
At this stage, we don't have enough information about the side effects of the vaccine, especially concerning any potentially severe ones.
We don't know how long the vaccine’s protection will last—could it be a few months, or will it last several years? With just a few months of data, it's impossible to answer that question.
The study groups were not fully representative of the entire U.S. population, though they did report that 42% of participants came from “diverse backgrounds.”
We don't yet know how effective the vaccine will be for children, as no participants under the age of 12 were included in the trials.
The study design, outlined in this Pfizer document, excluded individuals with serious health conditions, those who had previously contracted COVID-19, and those who were pregnant or breastfeeding. This means that many high-risk groups were not part of the study, but they will still require protection from the virus. Pregnant women are more likely than their non-pregnant counterparts to experience severe COVID-19.
What happens next
Pfizer intends to request emergency use authorization from the FDA later this month, once they meet the condition of having followed at least half of the participants for two months after their final dose.
Pfizer’s vaccine candidate is just one of many, and there’s no guarantee that it will be the first or the only one to reach the market. It's very possible that, by next year, we will have to choose from multiple vaccine options, some of which may prove more effective than others.
Manufacturing vaccine doses takes time, and health authorities have stated that the priority for any vaccine will be to distribute it first to those who are at high risk. However, there is still no clear plan outlining who will be the initial recipients. The most optimistic projections suggest that a vaccine—whether this one or another—could be available as early as January 2021.
