Where We Stand With the Most Promising COVID Vaccine Candidates in the World

Six months after the COVID-19 pandemic was officially declared, a handful of promising vaccine candidates may soon become powerful tools to prevent the virus from spreading any further.

There are over 100 vaccines currently in development around the world, with at least 40 in human clinical trials, according to The New York Times. A smaller number have reached the last stage of trials, Phase 3, or have already been approved for limited use. Multiple vaccines are likely to become available within months, shaving years off the typical vaccine timeline.

The three vaccines that are currently in advanced stage U.S. clinical trials are among the most promising. Pfizer and Moderna both have vaccines currently undergoing large scale randomized Phase 3 clinical trials, while Phase 3 trials for AstraZeneca's vaccine could soon resume after being forced to pause over safety concerns.

Early trials showed promising immune responses for all three candidates, stimulating the production of potentially virus-killing antibodies and triggering T-cell responses. Few serious side effects were observed.

However, trials for the AstraZeneca vaccine were temporarily put on hold due to one trial participant suffering severe inflammation to their spinal cord, according to PBS Newshour. It is not clear whether the illness was related to the vaccine or what effect it could have on the development of the vaccine.

The trio of vaccines in advanced U.S. trials are part of the Trump administration's Operation Warp Speed initiative, which aims to develop vaccines and treatments for COVID-19 at an unprecedented pace. Several other vaccines in earlier stages of development are also part of the initiative, including candidates from Johnson and Johnson, Norovax and Sanofi.

The U.S. does not have a monopoly on conducting accelerated research to develop a coronavirus vaccine. Researchers from around the world are being aided by massive investments of money and resources, relaxing of regulations and newer techniques that can develop vaccines far faster than traditional techniques.

While there have been hints that the FDA could approve a vaccine for emergency use in the U.S. before November's election, as President Donald Trump has repeatedly pushed for, none are likely to have completed their Phase 3 trials before then.

Phase 3 trials are the last and most crucial step in determining if a vaccine or drug is actually safe and effective. It is not uncommon for candidates to show promising results in early trials but then fail at the last hurdle. A 2018 study from the journal Biostatistics found that two out of three vaccine candidates ultimately fail to be approved.

A number of vaccines developed in China and Russia have already been approved for limited use, despite a lack of any conclusive evidence that they are safe or effective.

Vaccines from China's CanSino Biologics and Russia's Gamaleya Research Institute are both being developed using other viruses that have been engineered to carry genetic material from the coronavirus. This technique is also being used by AstraZeneca candidate and has yielded many successful vaccines against other illnesses in the past.

Three other vaccines being developed in China have also already been approved for limited use, one from SinoVac Biotech and two from Sinopharm. These vaccines use an inactivated form of the coronavirus, a method that has produced many successful vaccines for other viruses, although it is too early to know whether the candidates are safe and effective due to incomplete research.

Many other candidates are being developed using messenger RNA, a promising newer technique that offers speed but has yet to produce a vaccine approved for use in humans. The Moderna and Pfizer vaccines are the most advanced to use this method, in terms of the amount of research that has been completed.

Newsweek reached out to the FDA for comment.