Even with early promising results from Pfizer's Covid-19 vaccine trial, significant challenges and unanswered questions remain before average Americans can get a shot. Pfizer's vaccine is a new type of technology that's never been used in mass human vaccination before and experts caution that much remains unknown about its safety, how long it might work and who might benefit most.
Pfizer's phase 3 clinical trial began in late July and has enrolled more than 43,000 study participants. Some received the actual vaccine, while other received a placebo. Vaccine trials rely on a certain number of infections to occur. If more infections are reported among study participants who received the placebo than the actual vaccine, it's a good signal of efficacy.
On Monday, the U.S. pharmaceutical giant Pfizer and its German partner, BioNTech SE, said that early analysis show that the Covid-19 vaccine is more than 90 percent effective at preventing symptomatic illness.
The finding exceeded expectations and was met with enthusiastic optimism — along with many caveats.
That's because the drugmaker has not released full details on its preliminary analysis.
Pfizer stated that about a third of its study participants have "racially and ethnically diverse backgrounds" but didn't reveal if there was stronger protection for particular age groups.
"We don't know anything about groups they didn't study, like children, pregnant women, highly immunocompromised people and the eldest of the elderly," Dr. Gregory Poland, director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota, said. And would people previously sick with Covid-19 be protected against reinfection? That remains unclear.
What's more, the Pfizer vaccine uses a brand new technology called messenger-RNA, or mRNA. It has never been approved for human vaccination before. Instead of using bits of virus to provoke an immune response, the mRNA trains the immune system to target the spike protein found on the surface of the coronavirus.
The spike is what allows the virus to invade human cells. In theory, blocking the spike would mean people wouldn't become infected with the virus.
"The exciting thing is that these types of vaccines can be manufactured pretty quickly," said Dr. Richard Besser, president of the Robert Wood Johnson Foundation and former acting director of the Centers for Disease Control and Prevention.
"The caution is that this would be the first mRNA vaccine to be used in humans, so it's important to look carefully at the safety data."
It is also important to get a sharper picture of Pfizer's claim of about 90 percent effectiveness. This first analysis only included data on 94 confirmed Covid-19 cases, meaning there is no proof yet that the vaccine prevented infection.