Will a COVID-19 Vaccine Be Safe?

Some of the science behind developing this new vaccine is already in place. “A lot of research went into creating vaccines for two other dangerous coronaviruses — the SARS coronavirus [in 2002] as well as the MERS coronavirus” in 2012, Schaffner says. As a result, many drug companies already have technology that they've been able to use. In the case of COVID-19, scientists have been able to identify the sequence for a key protein on its surface called a spike protein. Moderna's vaccine transports a genetically engineered version of this spike protein via RNA, for example, while other companies, like Johnson & Johnson and AstraZeneca, use a weakened version of the adenovirus (the virus that normally causes the common cold). Each of these two approaches would stimulate your immune system to fight the disease caused by the virus so that you develop immunity to that disease, without exposure to the disease itself, Mulligan says.

The FDA also issued guidelines June 30 to outline what's expected for companies developing a potential COVID-19 vaccine, stating that it “will not cut corners.” This means that vaccine developers will be expected to undergo the rigorous clinical trial process all other vaccines have gone through, says vaccine expert Anna Durbin, M.D., professor of international health at the Johns Hopkins Bloomberg School of Public Health. Here's a look at what that entails.

Phase 1: Testing begins on a small group of young, healthy people.

Scientists test the vaccine in a small group of volunteers — usually 20 to 50 — to see if they develop an immune response. Subjects also are monitored for side effects. “These are done in young, healthy people who already have pretty robust immune systems, for safety reasons,” Durbin says.

Phase 2: The number of test subjects expands.

Next, testing expands to hundreds of people. “We tend to expand our criteria a bit, but we still avoid anyone with underlying health conditions, or who is immunocompromised,” Durbin says. This stage of the research normally takes one to two years, but due to pandemic concerns it will be compressed into a couple of months. “We usually don't have many long-term safety concerns when it comes to vaccines — we're more worried about anything that might crop up immediately or in the days after vaccination, such as anaphylaxis,” Durbin says.

Phase 3: Testing is done on those over 65 and other groups previously excluded from the trials.

In this stage, the vaccine is administered to tens of thousands of healthy people in areas particularly vulnerable to COVID-19. “The goal is to see how many contract the disease in an area where the virus is circulating,” Durbin says. Groups particularly susceptible to COVID-19 — including the elderly and those with preexisting health conditions — are now included. “We want to make sure at least a quarter of people in these trials are over the age of 65, to make sure it's effective in that age group,” Durbin says. Phase 3 trials normally take anywhere from one to four years, but vaccine developers hope to speed up this part of the process by creating as large a trial as possible, with at least 30,000 people.

While this stage of the clinical trial is going on, the vaccine manufacturer will begin to ramp up production. “The vaccine manufacturers are making a gamble that their vaccine will work,” Schaffner says. “If it does, we'll have warehouses of vaccine ready once the product gets FDA approval. But if it doesn't, all we've lost is money.”

Phase 4: The product goes to market, and monitoring begins.

Though the vaccine at this point would be widely available for sale, federal agencies, including the CDC and the FDA, would continue to monitor it for safety and efficacy. “This part of the process will be particularly important, as we will only be approving a COVID-19 vaccine based on efficacy and safety data from four to six months,” Durbin says. “We'll want to follow people closely to measure antibody levels, to make sure they are still immune, as well as watch for potential long-term safety complications."

That doesn't mean that a new COVID-19 vaccine won't carry risks. “We do have all these safety protocols in place, but we are still taking a risk licensing one without long-term safety follow-up,” Durbin acknowledges. “It's somewhat of a trade-off: We either license a vaccine early, with the hope that we can save lives, or we can wait two years, knowing that will lead to more hospitalizations and deaths. It is a risk calculation, but if we take the right precautions, it's most likely worth it."