FDA Sets Bar for COVID-19 Vaccine Approval at 50 Percent Effectiveness

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FDA Sets Bar for COVID-19 Vaccine Approval at 50% Effectiveness


While the U.S. and the world have largely fast-tracked efforts to develop a vaccine against COVID-19, experts in the field of immunology and virology have expressed concerns about the speed with which those efforts are moving. The U.S. Food and Drug Administration (FDA) issued guidelines today for where it will set the bar for approval of a vaccine, and that bar may not be as high as many would like.

First off, the agency indicated that it will require the vaccine be at least 50% more effective than a placebo in preventing COVID-19. That’s not likely to dazzle people, putting it about equivalent to a flu shot’s effectiveness in a good year. According to the U.S. Centers for Disease Control and Prevention (CDC), since 2010, the seasonal flu vaccines’ efficacy has ranged from 19% to 60%. According to the World Health Organization (WHO), no vaccine is 100% effective, although some routine childhood vaccines, such as those for measles, run about 85% to 95%.

Many experts and models have suggested that a vaccine with at least 70% effectiveness is needed to completely stop the spread of a virus, but it would need to be given to 60% of the population within 90 days of an outbreak.

One reason even those people for whom those vaccines turn out to be ineffective is because so many people in the U.S. are vaccinated for them, which is an example of so-called “herd immunity.” Some polls of Americans have indicated up to half may refuse to get a vaccine against COVID-19, at least when it’s first available.

The FDA guidelines also indicated a vaccine would not be approved unless it had “clearly demonstrated” proof of the vaccine’s safety and effectiveness in a clinical trial. It also said a vaccine would not be approved if it only results in antibodies in patients’ bloodstream, since it is yet unknown what level of antibodies leads to protection against the virus. This suggests companies and regulators will be closely watching population studies of the trial participants to determine if fewer percentages of inoculated individuals acquire COVID-19 compared to the placebo groups and the general population. This could be difficult if the patients are in areas of the world where the outbreak is dwindling.

In addition, the agency will require the vaccine manufacturer to run more safety monitoring after approval and that people getting the vaccine should be followed for at least a year after receiving the vaccine.

Stephen Hahn, commissioner of the FDA, said in response to senators’ questions in today’s hearing, “We have not lost sight of the need to protect our regulatory independence.” He also expressed optimism that potential therapies like convalescent plasma and monoclonal antibodies will play a big part in treating COVID-19 this fall.

The WHO’s benchmarks for a COVID-19 vaccine are more stringent than the FDA’s, calling at the high end for 70% efficacy and a duration of protection of one year, and at the lower end for 50% efficacy for six months.


The FDA has, at this point, two primary approaches to approving a COVID-19 vaccine. They are full approval or emergency use authorization (EUA). For the vast majority of clinical diagnostic tests for COVID-19 and for the only drug, Gilead Science’s remdesivir, the EUA has been the pathway. The FDA indicates full approval of a vaccine would require approximately 30,000 people to enroll in a Phase III clinical trial. That’s the number that Moderna’s Phase III trial for mRNA-1273, it’s messenger RNA vaccine against COVID-19, is expected to enroll and begin dosing in July.

It should be noted that the FDA granted the anti-malarial drugs hydroxychloroquine and chloroquine EUA to treat COVID-19, but have since been debunked as being ineffective and potentially making the disease worse. The FDA canceled the EUA on June 15.

Although EUA would be faster than full approval, it would still require the vaccine maker to demonstrate through a clinical trial that the vaccine resulted in fewer cases of the disease.

According to the WHO, as of yesterday there are 17 COVID-19 vaccines in human testing. More than 130 vaccines are being tested in the laboratory and in animals around the world.


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