En español | Researchers around the world have wasted no time in the race to find a vaccine to combat COVID-19. Six months into the pandemic, several vaccine candidates are already in late-stage clinical trials to test how well they protect people from a coronavirus infection. And some experts predict that by the end of 2020 or early in 2021, a safe and effective option will emerge.
“This is the scientific world working at warp speed,” Barry Bloom, a professor of immunology and infectious diseases and former dean at the Harvard T.H. Chan School of Public Health, said in a Sept. 15 webinar.
Beyond the development of the medicine itself, efforts to speed up vaccine manufacturing and distribution are also in place. Here’s a look at the coronavirus vaccine prospects and the progress being made on them.
What, exactly, is a vaccine?
A vaccine is something that helps a person build up immunity to an infectious disease. It works by intentionally introducing the body to an inactive form of a disease-causing germ, or something similar to it. This then stimulates the immune system’s production of antibodies, the proteins that help to protect the person from a future infection if they ever come across the real germ.
Think of it like a workout for your immune system: You’re “sending it to the gym and preparing it to be able to do something when it encounters the real thing in the future,” says Tony Moody, M.D., associate professor of pediatrics and immunology at Duke University School of Medicine and a principal investigator at the Duke Human Vaccine Institute. “Essentially, what a vaccine is doing is teaching the immune system how to handle something before you actually encounter the real thing — so that, hopefully, when you do encounter the real thing, you’re able to deal with it quickly and get rid of it.”
In the case of the new coronavirus, a vaccine would make a person resistant to an infection from the virus and the illness it causes — COVID-19 — or, at the very least, make it so that a person who becomes infected has “a shorter course [of disease] or not as many complications,” Moody adds.
Which coronavirus vaccines are leading the pack?
Of all the coronavirus vaccine candidates in the pipeline, four are considered the front-runners: a vaccine from Moderna and the National Institutes of Health (NIH); one from BioNTech and Pfizer; one from AstraZeneca and the University of Oxford; and another from Johnson & Johnson.
What makes these vaccines special? All four are in the third phase of testing in U.S. trials — “and that’s where the proof is in the pudding, so to speak,” says William Schaffner, M.D., an infectious disease specialist and professor of preventive medicine at the Vanderbilt University School of Medicine.
A phase 3 clinical trial is when researchers study the safety and effectiveness of the vaccine candidates against a placebo in a large population. (Moderna and AstraZeneca are testing their vaccines in about 30,000 volunteer participants; BioNTech and Pfizer announced their effort will enroll up to 44,000 participants; and Johnson & Johnson will enlist up to 60,000 volunteers across three continents.) They will also be able to see how well these vaccines work in populations that are most likely to get severely ill from a coronavirus (SARS-CoV-2) infection, including older adults, people with underlying health conditions, and racial and ethnic minorities, who have higher rates of hospitalization and death from COVID-19.
“Because if the vaccine can’t work well in the people who need it the most, then obviously we need a better vaccine or a different strategy,” says Jesse Goodman, M.D., director of Georgetown University’s Center on Medical Product Access, Safety and Stewardship (COMPASS) and former chief scientist at the Food and Drug Administration (FDA).
The vaccines from Moderna and BioNTech/Pfizer utilize a new technology, known as mRNA, which introduces a genetic code the body can use to make its own viral protein to induce an immune response. AstraZeneca’s vaccine uses a nonreplicating chimpanzee adenovirus to deliver a SARS-CoV-2 spike protein to stimulate an immune response, and Johnson & Johnson’s one-dose vaccine is made from a genetically modified adenovirus.
Just because these four are leading the pack, however, doesn’t mean the other vaccine candidates out there — all 213, according to the Milken Institute’s vaccine tracker — are out of the race. Seven additional vaccines are also in phase 3 trials around the world, a database maintained by the New York Times shows, and nearly 50 others are in phase 1 and 2 studies, some of which employ “more traditional technologies that are used in currently approved vaccines,” Goodman explains.
Can more than one vaccine candidate work and be approved?
Absolutely. “In fact, it’s highly desirable,” Schaffner says, because that would mean “there would be more vaccine manufacturers working to actually produce the vaccine, and so we could more expeditiously try to vaccinate the population in the United States and beyond.”
Kathleen Neuzil, M.D., professor in vaccinology and director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine, echoes Schaffner’s sentiment and points to the flu vaccine for comparison: There are multiple formulations on the market, including the injectable high-dose vaccine and the nasal spray vaccine, for example, which are recommended for different populations.
“We really need every person on earth, theoretically, to be able to receive this vaccine. So, to me, [having more than one option] is a positive, because we need so much,” she adds.
When will a coronavirus vaccine be approved?
It’s hard to pinpoint when a vaccine will get the go-ahead from the FDA — that all depends on when scientists are able to collect enough data from the phase 3 clinical trials to know for sure whether the vaccine is safe and effective at preventing a coronavirus infection or decreasing its severity in at least 50 percent of vaccine recipients. (The 50 percent efficacy standard was set by the FDA in June. For comparison, the influenza vaccine is between 40 percent and 60 percent effective.) That said, most health experts say it’s reasonable to expect an approved vaccine by the end of 2020 or early in 2021.
One thing that could delay the process: the rate at which clinical trial participants get infected. In order for the trials to show that a vaccine candidate works, some participants need to contract the coronavirus out in the community. (They are not being introduced to SARS-CoV-2 in the lab, as of now.) As Harvard’s Bloom puts it: “The end point is the number of people who get sick; it’s not a calendar date.”
As Schaffner points out, the population that typically volunteers for clinical trials is the same population that is more likely to adhere to public health guidance put in place to prevent the spread of COVID-19. “They’re usually the type of people who, in the COVID era, are being very careful. They’re social distancing; they’re wearing masks. They don’t go out to restaurants; they haven’t traveled,” Schaffner says. “And some of us think that these trials may have to run a little longer than people anticipated for just that reason. Because the volunteers tend to be very careful people.”
An adverse reaction to a vaccine candidate could also slow the process. Both AstraZeneca and Johnson & Johnson recently paused their trials to investigate a participant who may have experienced a complication from the vaccine. (The two companies have since announced that they have been cleared to resume research.) Bloom says while this delays things a little bit, “it proves that the system is working.” Pointing to the trial’s safety measures in place, he adds, “It is exactly what should be done when anybody is sick.”
When will a vaccine be available to the public?
As soon as possible. In a Sept. 16 hearing before a Senate committee, Centers for Disease Control and Prevention (CDC) Director Robert Redfield, M.D., said once the FDA green-lights a vaccine, the government “wants to be in a position to distribute it within 24 hours.”
That does not mean everyone who wants a vaccine will be able to get one immediately. Public health experts and government leaders are working on distribution and prioritization plans. (The CDC recently posted information on preliminary recommendation and distribution plans to its website.) Schaffner says it’s likely that health care workers will be at the front of the line to receive the vaccine, but older adults and people with underlying health conditions will be “very near to the first in line.”
Even so, it’s important to keep in mind that it will likely take “six to nine months to get the American public vaccinated,” Redfield said.
If a vaccine is not 100 percent effective, can I still get COVID-19?
That may be the case, although more details on the vaccine’s effectiveness should emerge in the third phase of clinical trials and in post-trial surveillance. And “that’s something that the recipients will have to understand when they get the vaccine,” Schaffner says. “The vaccine provides protection, but it won’t be like a suit of armor.”
His main message: Just because you roll up your sleeve and get the shot doesn’t mean you can throw away your mask and disregard other prevention efforts such as social distancing and handwashing. Those will be crucial “for quite some time” in order to get control over the virus, Schaffner says. Another consideration: An approved vaccine will likely require two doses, several weeks apart, which will stretch out the time before it is effective in recipients. (Johnson & Johnson’s one-dose vaccine candidate is the exception.) The duration of immunity from the vaccine is also unclear at this point. “It’s possible people will need boosters before we’re done with all this,” Goodman adds.
Finally, future coronavirus vaccines could be more effective, both at saving lives and in slowing the spread of the virus, compared to the first few approved. “The best of them, which may not be in the first slot, are those that also prevent people who are infected from transmitting to everyone else,” Bloom says. “And if we have such vaccines, and they’re available to the world, we can stamp out this COVID-19 epidemic worldwide.”
Why does the vaccine development process take so long?
Though timelines may seem long and “frustratingly inefficient,” the speed at which the coronavirus vaccine process is moving is unprecedented, says Duke’s Moody.
Vaccine development typically takes 10 to 15 years, and the fastest vaccine created thus far was for mumps — that process took four years. What’s more, after a vaccine is approved, it can take months to years to scale up manufacturing and production for widespread distribution. The U.S., however, already has a head start on this.
To date, the federal government has invested billions of dollars to stockpile doses of a few vaccine candidates so that if and when they prove to be safe and effective in clinical trials, they will be readily available for the American public.
“I think it’s really important for people to understand that the response to this pathogen has been faster than any other pathogen in history,” Moody says. “The fact that you had a virus that was first reported in China in December, and by March we were already talking about setting up a phase 1 trial … I think the speed of the response, both by the medical community and by everyone else, is actually pretty astonishing.”
What if scientists don’t come up with a coronavirus vaccine that works?
That’s unlikely at this point, but it is a possibility. And that’s why it’s important to pursue treatments for COVID-19, as well, Moody says.
“If we had sort of the Tamiflu equivalent for coronavirus where you could be exposed and take Tamiflu and be protected, or you could get early disease and it could attenuate the disease or shorten the course, that would be great,” Moody says of the antiviral treatment for influenza. “There’s a lot of work being done there. And I think all of that work needs to proceed as well.”
The FDA has so far approved the antiviral drug remdesivir for treatment of some patients hospitalized with COVID-19; the agency issued an emergency use authorization (EUA) for convalescent plasma to treat people who are hospitalized with the illness. An EUA is not the same as official FDA approval, and studies are still continuing to evaluate these therapies and others.
The World Health Organization has also issued guidelines that recommend the use of inexpensive and common corticosteroids such as hydrocortisone and dexamethasone for the treatment of patients with severe cases of COVID-19. The guidelines come after an analysis of several clinical trials found that corticosteroids cut the risk of death in patients hospitalized with COVID-19. The new guidelines, however, emphasize that steroids should not be used to treat patients with mild symptoms of the disease.
Editor's note: This article, originally published May 1, has been updated to reflect new information.