Health experts had raised some concerns over Pfizer's COVID-19 vaccine. They said that the shot might be safe and effective, but many questions are left unanswered.  

Pfizer
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Pfizer's logo is reflected in a drop on a syringe needle in this illustration.

Pfizer's COVID-19 vaccine has shown promising results during Phase 3 or the last human clinical trial stage. The vaccine developed by Pfizer and its partner BioNTech is said to be 90 percent effective based on the data that they have. 

Read also: COVID-19: Analysis Shows Pfizer's Vaccine is 90% Effective in Phase 3 Trial 

Despite the promising result, health experts raised concerns about the vaccine. They raised many questions, most especially that Pfizer used a new type of technology that has never been used in mass human vaccination. Much remains unknown about its safety, how long it will work, and who might benefit from it. 

The U.S. pharmaceutical giant and its German partner, BioNTech SE, announced Monday that the vaccine they developed is 90 percent effective at preventing symptomatic illness, according to an NBC News report.

The companies even claimed that their findings have exceeded what was expected from them. However, experts raised some concerns over its promising results, mainly because the companies did not give details on its preliminary analysis.  

Read also: Meet the Two Latino Health Experts Leading Biden's COVID-19 Task Force 

Pfizer said there were around 44,000 persons in the U.S. and other countries who participated in the human clinical trial's last stage.

Around a third of these numbers were from racially and ethnically diverse backgrounds. But they did not indicate in their study if there was stronger protection for particular age groups. 

Dr. Gregory Poland, director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota, said: "We don't know anything about groups they didn't study, like children, pregnant women, highly immunocompromised people and the eldest of the elderly." 

He also questioned if those people who were previously infected with the virus will be protected against reinfection.

One of the reasons that alarmed some experts is that Pfizer used a brand new technology called messenger-RNA or mRNA. This technology has never been used for human vaccination before. 

The mRNA trains the immune system to target spike protein found in the virus responsible for COVID-19. That means that a person will not become infected with the virus by blocking the spike using the mRNA.  

Even though some experts are quite skeptical about the potential COVID-19 vaccine, some also supported it.

Dr. Richard Besser, president of the Robert Wood Johnson Foundation and former acting director of the Centers for Disease Control and Prevention, said the good thing about these types of vaccines is that it can easily and quickly be manufactured. 

However, he agreed that the only caution is that it is the first mRNA to be used in humans. He also stressed the importance of looking into data. 

As reported by Latin Post, the U.S. FDA said the data came too early to conclude that Pfizer's COVID-19 vaccine is safe and effective.