American drug maker Pfizer announced Monday that its COVID-19 vaccine is at least 90 percent effective, based on initial data from the company’s clinical trial.
To better understand what we know (and what we don’t) about the company’s announcement, we spoke with San Diego scientists and doctors deeply involved in researching COVID-19 treatments.
What we know
This is good news
UC San Diego infectious disease specialist Dr. Davey Smith and Scripps Research immunologist Dennis Burton summed up their reactions in one word: “Great.”
Pfizer’s announcement is based on initial data from a massive clinical trial that has enrolled more than 43,000 participants from São Paulo to San Diego. Roughly half the volunteers received two injections of the company’s experimental vaccine, while the other half received a placebo.
An independent team of scientists not affiliated with the company or federal regulators reviewed data from 94 trial participants who got COVID-19. The reported efficacy of more than 90 percent suggests that very few people who got the vaccine got COVID-19.
If that percentage holds up, it would exceed many scientists’ expectations. Some vaccines, such as those for measles and human papillomavirus, are nearly 100 percent effective. By comparison, your average flu shot is about 40 to 60 percent effective. The Food and Drug Administration has set the bar for any would-be COVID-19 vaccine at a minimum of 50 percent efficacy.
“It’s really hopeful,” said La Jolla Immunology researcher Erica Ollmann Saphire. “We had steeled ourselves for moderate efficacy.”
Hold onto that mask. This pandemic isn’t going away any time soon
There’s no question Pfizer’s announcement is encouraging. Just like how there’s no question a vaccine won’t be a panacea, say UCSD’s Davey Smith.
“Let’s not get complacent with this: The vaccine isn't going to fix everything,” Smith said. “If we still use masks and social distancing and (are) prudent in those areas, then we can get the pandemic better under control.”
Pfizer’s vaccine has raised hopes and moved markets, but any vaccine likely won’t be available to most people until the summer of 2021 or later, according to the director of the Centers for Disease Control and Prevention.
The company plans to apply to the FDA for emergency use authorization later this month. It then faces a new set of challenges: production, storage and global distribution. Pfizer says it could have 50 million doses available by the end of this year and produce another 1.3 billion in 2021.
There are 7.7 billion people on the planet, and each person who gets the vaccine will need two doses.
The bottom line: This vaccine won’t be available to everyone instantly.
This bodes well for other COVID-19 vaccines in development
There are close to 200 ongoing COVID-19 vaccine efforts worldwide, and Pfizer’s announcement is probably good news for most of them, says Dennis Burton, whose lab at Scripps has worked for years to help develop an HIV vaccine and is now using those tools to study COVID-19.
“There's a great sense of relief that, as many had thought, it might not be so difficult to make an effective vaccine against this virus,” Burton said.
One of the vaccine developers most likely to be encouraged by Pfizer’s announcement is Massachusetts biotech Moderna, which began its large-scale vaccine trial July 27, the same day as Pfizer. Both companies’ vaccines use a molecule called messenger RNA that teaches the body to recognize the novel coronavirus and attack its surface.
Having multiple COVID-19 vaccines would be a good thing, as some vaccines may work better for certain populations (such as older adults) or be easier to transport. For example, some vaccines in development can be kept on ice or even at room temperature, whereas Pfizer’s vaccine must be kept at a bone-chilling minus 94 degrees Fahrenheit.
What we don’t know
How long protection from Pfizer’s vaccine lasts
It’s one of the biggest unanswered questions. It’s also impossible to answer right now, Saphire says.
“You won't know until six months if it lasted six months. You won’t know until a year if it’s lasted a year,” she said.
Some vaccines trigger long-lasting immunity, which is why you only need a tetanus booster shot once a decade. But you need a new flu vaccine each year because the virus mutates rapidly.
The novel coronavirus has not mutated much so far. And while that could change, that’s a good sign.
But about 11 months into this pandemic, there have already been cases of people getting COVID-19 twice. So far, those cases are rare, and mostly lead to mild or no symptoms. Perhaps the same will be true of those who get a vaccine. Pfizer plans to keep monitoring trial participants for the full two-year period of its study, which will likely shed more light on the matter.
How well the vaccine prevents infection, transmission and severe illness in different groups of people
A perfect vaccine would quash infection in people of all ages and backgrounds. That’s the hope.
Here’s the reality: Even if a vaccine doesn’t prevent you from getting sick, it can still lower your chances of infecting someone else, ending up in the hospital or dying.
“All of those are good, more is better,” Saphire said.
Knowing how well the vaccine does any of those things is important, she says. For example, Pfizer’s 90 percent vaccine efficacy is based on preventing people from getting sick with COVID-19. But nearly half of people with COVID-19 never develop symptoms, according to the CDC’s best guess, though they can still spread the disease. So it would also help to know how well the vaccine reduces asymptomatic cases.
When this pandemic will be over
Any COVID-19 vaccine would be a tool, not a silver bullet, Smith says.
How useful that tool is will depend on two things. One is how well we adhere to public health guidelines, even after a vaccine is available. Another is how many people are willing to get a vaccine.
It boils down to math for Smith. On average, without any masks, social distancing or other precautions, one person with COVID-19 will infect about four others. That's a recipe for uncontrolled spread.
Simply wearing a mask, washing your hands and avoiding indoor gatherings slows that spread. So would a vaccine. Smith estimates that at least 75 percent of people would need to take a COVID-19 vaccine to quell the pandemic: “Even (with) a vaccine that works 90 percent of the time, the vast majority of people still have to take it to wipe out an epidemic."
