Pfizer’s COVID-19 vaccine has a 90% efficacy rate: what does that mean?


Pfizer and the German company BioNTech SE announced on Monday a vaccine candidate for COVID-19, against which the world has been fighting since the beginning of this year. According to the companies, BNT162b2 has proven successful in the first interim analysis from the Phase Three study.

Pfizer initiated Phase three of the clinical trial on July 27, with 43,538 participants. Participants in the “blinded” study will receive either the vaccine candidate or a saltwater placebo, which means that no one but the independent committee knows which one the patients received, the New York Times reported.

Of the 43,538 participants, 94 exhibited symptoms of coronavirus, indicating that the effectiveness of the vaccine is 90 percent, which is the percentage of participants who received the vaccine and did not show symptoms.

A total of 38,955 participants had received the second dose by November 8.

Although the vaccine appears promising, the study must continue until 164 cases of corona virus have been reported and there are still unknowns.

Efficacy vs. effectiveness

Pfizer’s report of an “efficacy rate of over 90%” has led many to believe that the vaccine is 90% effective. However, there is a difference between the two.

Zania Stamataki, a virus immunologist at the University of Birmingham, explains the difference in an article with The Conversation. “…efficacy is the performance of a treatment under ideal and controlled conditions, and efficacy is the performance under real conditions,” Stamataki said.

What does this mean for the study? Clinical trials take place in a controlled environment to test whether the vaccine is safe and whether it works. The 90 percent efficacy rate means that COVID-19 symptoms were prevented in 90 percent of participants who received the vaccine, although Stamataki predicts that this number will change by the end of the study.

It is expected that vaccines with a 50 percent efficacy rate for COVID-19 will be approved, Stamataki said.

Is the vaccine safe?

The data review panel from the analysis of the Phase Three trial has not reported any “serious safety concerns.

Pfizer and BioNTech are still collecting safety data, and Stamataki expects that the safety data needed for potential emergency FDA approval – a median of two months of safety data collection after the second (and final) dose of the vaccine – will be released in the third week of November.

In addition, study participants will continue to be monitored for “long-term protection and safety” for two years after their last dose of the vaccine is released.

What does this mean for the public?

“Pfizer’s CEO said the company could have 30 to 40 million doses of the vaccine before the end of the year, enough for 15 to 20 million people to receive a first vaccination and a booster three weeks later,” the New York Times reported. It is not known who will receive the vaccine first, but it is likely that high-risk groups and frontline workers will be targeted.

“About 42% of participants worldwide and 30% of participants in the U.S. have racially and ethnically diverse backgrounds,” Pfizer said.

Pfizer and BioNTech estimate that they will produce up to 1.3 billion doses of vaccine in 2021, but that is far from the number needed to meet global demand. If other companies have a proven track record of successful vaccines, the demand could potentially be met. According to the New York Times, ten more vaccines are currently in late stage trials worldwide.

Until a vaccine is approved, and possibly beyond, health professionals and officials are urging the public to remain socially aloof and wear a mask.


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