COVID-19 vaccine candidates show promising early results, but finish line still far ahead

A flurry of research, newly released by multiple manufacturers of COVID-19 vaccine candidates, provides reassuring glimmers of hope that scientists are on track to develop an effective and safe vaccine at record speed.

On Monday, three research groups separately released early positive results demonstrating that their respective COVID-19 experimental vaccines induced a multipronged immune response that may be important for long-term protection against infection.

Those groups included the University of Oxford and its partner AstraZeneca, Pfizer and its partner BioNTech and the Chinese vaccine company CanSino Biologics. Last week, Moderna also released promising early data.

Experts caution that these early studies, though promising, will need to be confirmed with larger Phase 3 trials, involving tens of thousands of people, to determine if any vaccine could be truly effective.

According to the World Health Organization (WHO), there are at least 23 COVID-19 vaccine candidates that have progressed to various stages of human studies. So far, several of these candidates have showed promising preliminary data from their early clinical trials, either in peer-reviewed journals, directly online to preprint servers or in press releases.

On Monday, new data by Oxford-AstraZeneca, published in the journal The Lancet, suggested that the vaccine is relatively safe and induces an immune response to fight the novel coronavirus. All 1,077 volunteers who received the vaccine in the Phase 1/2 trial developed neutralizing antibodies against COVID-19. These specific antibodies are infection-fighting proteins produced by the body that may prevent the virus from infecting healthy cells. The vaccine also elicited a T-cell response to the virus: another method of defense used by the immune system to bolster protection and attack cells already infected by the virus.

Professor Adrian Hill, director of Oxford's Jenner Institute, called the latest data very "encouraging" in an interview with ABC News, adding that experts are "seeing both arms of the immune systems stimulated very strongly by the vaccine."

Meanwhile, BioNTech and Pfizer also released results of a Phase 1/2 trial Monday. That study included 60 participants and showed that the vaccine induced both neutralizing antibody and T-cell responses. The results were published in a preprint server, meaning they have not yet undergone the normal scientific review process.

Also on Monday, CanSino Biologics released data in the Lancet that showed similar results. And last week, the U.S.-based company Moderna released data in the New England Journal of Medicine that also demonstrated this two-pronged effect of neutralizing antibodies and T-cell response.

Francis Collins, director of the National Institutes of Health, told ABC News that many of the vaccines with recently-published data look promising.

"Their Phase 1 data looks really good," Collins said, referring to Oxford's vaccine. "I wouldn't say it looks distinctly better than what you see for the Moderna trial or the Pfizer trial. They all look good, which is really encouraging to see."

Collectively, these early studies indicate that all four vaccine candidates might confer immunity through multiple pathways to fight COVID-19, although experts caution that more research is still needed.

Dr. Paul Goepfert, director of the Alabama Vaccine Research Clinic at UAB, said that "distinguishing one vaccine candidate from another is very difficult at this point. They all induce about the same amount of responses. They all induce neutralizing antibody response, which is sort of the gold standard of protection for a lot of vaccines."

According to Goepfert, antibodies protect against infection, while T-cells -- especially a specific subtype known as killer T-cells -- attack previously-infected cells and are very good at preventing disease.

"So ideally, you want everything. The more the merrier," said Goepfert, "The more types of immune responses you can induce with the vaccine, and the higher amount, we think that's the best thing you can have."

But he warned that this is not always the case. Some effective and already widely-used vaccines, like the Hepatitis B vaccine, do not induce any killer T-cell response but are still highly effective.

Although the results reported this week are promising, it's still too early to predict which one of the vaccines will be the most effective. Early Phase 1 and Phase 2 studies mainly examine vaccine safety, tolerability and immune response, but Phase 3 trials will provide answers to these much-anticipated questions about efficacy.

Even Hill admitted that the Oxford team still doesn't have the data to determine how well their vaccine will actually work. "The truth is that we don't know when we'll have a final result or how well the vaccine works," Hill said. "It's likely to be months. We were aiming for September, October... I still think that's a realistic aspiration but we can't be certain."

When it comes to large Phase 3 studies, Oxford is slightly ahead of the pack, having already enrolled over 10,000 people in Brazil, South America, the U.K. and, soon, in the U.S.

"We're aiming to vaccinate, in total, around about 50,000 people over the coming months, so that's promising, but you know it's not really a race against other vaccines, it's a race against time," Hill added. "But at the moment we're probably ahead in terms of Phase 3 trials and hoping to get a result certainly this year."

Among European and North American vaccine efforts, Moderna is following right behind, scheduled to begin its Phase 3 trials next week. Similarly, Pfizer-BioNTech is on track to launch its Phase 2/3 trial later this month.

Among Chinese companies, two have already begun Phase 3 trials: Sinovac and Sinopharm. According to CanSino Biologics' executive director, Qiu Dongxu, the company is expected to begin Phase 3 trials "soon," but a clear start date is yet to be publicly released.

Biopharmaceutical companies across the world have now pivoted their efforts to primarily support the development of COVID-19 treatments and vaccines. Progress has been made at record speeds, and during an unprecedented time, the U.S. government is taking unprecedented measures, ramping up the development of some of these vaccines before even confirming their efficacy.

According to Dr. Anthony Fauci, the nation's top infectious disease doctor, "If everything works out the way we hope and we don't get any unpredictable potholes and bumps in the road, we should know, as we get into the mid to late fall, early winter, probably late fall, whether we have candidates that really are safe and effective."

Many scientists and researchers have been working nonstop for the past six months to find a vaccine against COVID-19.

"We feel that there's urgency and pressure really every day," Hill said. "People are working day and night and we're not going to stop until we get an answer."

Eden David, who studied neuroscience at Columbia University and is matriculating to Icahn School of Medicine at Mount Sinai later this year, is a member of the ABC News Medical Unit. Sabina Bera, M.D., M.S., a psychiatrist in New York, and Shantum Misra, M.D., a senior resident in internal medicine at Dartmouth-Hitchcock Medical Center, are contributors to the ABC News Medical Unit.