Vaccine trials show promising results, but major challenges lie ahead

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Two potential coronavirus vaccines have shown promising results in early trials, and although experts say this is encouraging news, they warn some of the biggest hurdles are yet to come.

Initial results from trials for the two candidate vaccines – one developed by the University of Oxford and AstraZeneca and the other by Chinese company CanSino Biologics – showed that both were safe and could induce immune responses in patients. participants. But the next phase will be crucial in demonstrating that potential vaccines can protect against infections.

“If we’re building an airplane, we’re at the production level right now,” said Dr. Carlos del Rio, executive associate dean of Emory University School of Medicine in Atlanta. “You could say it looks like it can at least take off and do it safely. But can that get me from here to Paris? That’s the question now. “

So far, vaccine development efforts have proceeded at an exceptional pace. Typically, it 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 there are already two dozen vaccine candidates undergoing clinical trials around the world.

For the Oxford-AstraZeneca and CanSino vaccine candidates, the next step in testing is phase three of human clinical trials. It is at this point that scientists will be able to see if a potential vaccine really works in preventing coronavirus infections. While it is not common for vaccine candidates that have performed well in the early stages to fail in later stages, it can happen, del Rio said.

“I can tell you in the world of HIV we’ve seen a ton of vaccines being immunogenic – they produce immune responses – and then you get them to phase three and they don’t protect you,” he said. declared.

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Still, the results have been positive so far, del Rio said.

The results of recently published clinical trials showed that the Oxford-AstraZeneca vaccine candidate triggered the production of antibodies and T cells, able to recognize and attack viral cells. The multifaceted immune response can be critical, as researchers are still trying to determine whether one is more important than the other for long-term protection.

“The immune system has different weapons, and normally we would spend maybe several years figuring out whether the vaccine should be very good at inducing antibodies or whether it should be good at inducing T cells or if you need one. combination, ”said Paula Cannon, associate professor of microbiology at the Keck School of Medicine at the University of Southern California. “But at the moment, we don’t have the luxury of time. “

The Oxford-AstraZeneca vaccine candidate has already moved on 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 begin similar efficacy trials in Brazil.

In addition to evaluating whether vaccines can prevent coronavirus infections, this testing step is designed to assess the performance of the potential vaccine in more diverse populations.

The first Oxford-AstraZeneca trials included 1,077 participants, but the vaccine candidate has not been tested in anyone over 55 years of age. The CanSino vaccine candidate has been tested on 508 people and included participants aged 55 and older, but more research is needed before any vaccine is available. is considered safe to be widely administered.

During phase three clinical trials, it’s crucial to expand and diversify the people studied, which means including people with demographics who have been disproportionately affected by the coronavirus, del Rio said.

“Here in the United States, I want to see the people most affected enroll in education,” he said. “We need African Americans, Hispanics and older enrolled populations. There is no benefit if we recruit a group of middle class whites who have a lower incidence of the disease. “

Scientists will also be on the lookout for dangerous side effects. In the first trials, the two candidate vaccines produced only minor side effects, such as fever and headache.

Pin Wang, a professor of materials science and biomedical and chemical engineering at the University of Southern California, said it was reassuring that the side effects seen so far have been manageable. And while it’s not uncommon to identify other issues later, both studies were large enough that major side effects would likely have already been seen.

“If there are other side effects, they are probably related to genetic makeup,” Wang said. “I think it’s rare with the number of people who have been tested that we miss anything big. “

But he didn’t rule out that more surprises could be in store as vaccine candidates undergo more detailed assessments. Part of the problem is that although vaccine development has progressed at a breakneck pace, researchers are still making discoveries about the coronavirus every day.

“This virus is new, and it is a challenge for vaccine development,” Wang said. “We don’t have all kinds of data to give us clues. We can only learn the answers to these questions by doing more study. “

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