Two possible coronavirus vaccines have shown promising results in early trials, and while experts say it’s encouraging news, they caution that some of the biggest hurdles are yet to come.
The first results of the trial for the two vaccine candidates, one developed by the University of Oxford and AstraZeneca and the other by the Chinese company CanSino Biologics, showed that both were safe and could induce immune responses in the participants. But the next phase will be critical to demonstrate that potential vaccines can protect against infection.
“If we are making an airplane, we are at the production level right now,” said Dr. Carlos del Rio, executive associate dean of Emory University School of Medicine in Atlanta. “We can say that it seems like this can at least take off and do it safely. But can it get me from here to Paris? That’s the question now.”
So far, vaccine development efforts have advanced at an exceptional rate. It usually takes about a decade for a new vaccine to go through the various stages of development and testing. But the urgency of the pandemic, which has killed more than 600,000 people worldwide, means that there are already two dozen candidate vaccines in clinical trials worldwide.
For the Oxford-AstraZeneca and CanSino vaccine candidates, the next step in testing is known as phase three of human clinical trials. It is at this stage that scientists will be able to see if a potential vaccine really works to prevent coronavirus infections. While it’s not common for vaccine candidates who have performed well in the early stages to fail in the later stages, it can happen, Del Rio said.
“I can tell you that in the HIV world, we have seen that a lot of vaccines are immunogenic, produce immune responses, and then it takes them to phase three and they don’t protect it,” he said.
Still, the results have been positive so far, del Río said.
The results of recently published clinical trials showed that the Oxford-AstraZeneca vaccine candidate triggered the production of antibodies and T cells, which can recognize and attack viral cells. The multiple immune response may be key, because researchers are still trying to figure out if one is more important than the other in providing long-term protection.
“The immune system has different weapons, and we would normally spend perhaps several years figuring out if the vaccine needs to be very good at inducing antibodies or if it needs to be good at inducing T cells or if it needs a combination,” said Paula Cannon, associate professor of microbiology at the Keck School of Medicine at the University of Southern California. “But right now, we don’t have the luxury of time.”
The Oxford-AstraZeneca vaccine candidate has already progressed to phase three clinical trials in Brazil, South Africa and the United Kingdom. Additional trials are expected to begin in other parts of the world, including the United States. The CanSino vaccine is expected to start similar efficacy trials in Brazil.
In addition to evaluating whether vaccines can prevent coronavirus infections, this testing step is designed to evaluate how the potential vaccine works in more diverse populations.
The first Oxford-AstraZeneca trials included 1,077 participants, but the vaccine candidate was not tested on anyone older than 55 years. The CanSino vaccine candidate was tested on 508 people and included participants age 55 and older, but more research is needed before any vaccine is considered safe to be administered widely.
During phase three clinical trials, it is crucial to expand and diversify the people being studied, which means including people from the demographics who have been disproportionately affected by the coronavirus, Del Rio said.
“Here in the United States, I want to see the most affected people enrolled in the studies,” he said. “We need to enroll African American, Hispanic and older populations. There is no benefit if we enroll a group of middle class white people who have a lower incidence of the disease.”
Scientists will also be on the lookout for dangerous side effects. In the first trials, both vaccine candidates produced only minor side effects, such as fever and headaches.
Pin Wang, professor of materials science and biomedical engineering and chemistry at the University of Southern California, said it’s reassuring that the side effects seen so far have been manageable. And while it’s not unusual to identify other problems later, both studies were large enough that significant side effects have already been seen.
“If there are other side effects, they are probably related to a genetic background,” said Wang. “I think it’s rare with the number of people who have been tested that we are missing something big.”
But he did not rule out that other surprises could be expected as vaccine candidates undergo more detailed evaluations. Part of the problem is that while development of the vaccine has been proceeding at a breakneck pace, researchers continue to discover the coronavirus every day.
“This virus is new, and that’s a challenge for vaccine development,” said Wang. “We don’t have all kinds of data to give us clues. We can only learn the answer to these questions by doing more studies.”
