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Moderna COVID-19 trial data shows vaccine is broadly effective

But the trial did not succeed in enrolling enough Black or Indigenous participants.

Medical staff at Howard University prepare COVID-19 vaccination doses for hospital staff on Monday.
Medical staff at Howard University prepare COVID-19 vaccination doses for hospital staff on Monday. (Tasos Katopodis/Getty Images)

The COVID-19 vaccine co-developed by Moderna and the National Institutes of Health is broadly effective, according to documents released by the pharmaceutical company and the Food and Drug Administration Tuesday.

The documents were prepared in advance of a critical meeting Thursday of the FDA’s outside advisors on immunology, vaccinology and epidemiology, who will decide whether to recommend emergency authorization for the vaccine. The data had been previously only been summarized in press releases. 

The document the FDA prepared on the vaccine shows that it is broadly effective. 

Virologists have worried for months that a vaccine may not generate strong enough protection in older Americans, who often do not produce as durable an immune response as younger people to the flu vaccine. Concerns also have swirled for months about underrepresentation of Black and Latino patients in the clinical trials.

About 14,000 people were in each arm of the clinical trial: 13,934 volunteers who got the shots, and 13,883 people who received a placebo. 

Of those, 7,026 were people over the age of 65. A total of 15 people in this age group got sick with COVID-19 and none of them received the vaccine, according to the federal briefing document — indicating 100 percent efficacy in this older population.

National Institute of Allergy and Infectious Diseases Director Anthony Fauci met with Moderna on its vaccine candidate on Zoom every weekend, and often strategized with the drugmaker and U.S. Surgeon General Jerome Adams on how to reach out to Black and Latino populations. Still, the investigators did not succeed in enrolling enough Black or Indigenous participants to ensure representation in the clinical trial matched the racial makeup of the U.S. population. 

The clinical trial enrolled 3,090 Black volunteers, making up 10.2 percent of all participants, while Black people comprise 13 percent of the U.S. population. The clinical trial enrolled 230 American Indian or Alaskan Native people, making up 0.7 percent of clinical trial participants, less than their 1.6 percent makeup of the U.S. population. But investigators did succeed in enrolling 6,234 Hispanic or Latino volunteers, making up 20.5 percent of participants, while they comprise 16 percent of the U.S. population. 

Four Black volunteers came down with COVID-19, while 12 Latino volunteers did. All of them received the placebo, not the vaccine, suggesting high efficacy. 

The clinical trials have been shortened because of the urgency of the pandemic, making it challenging to enroll enough people who will get very sick with COVID-19 in an abbreviated amount of time, though rampant transmission in the U.S. made meeting that metric easier. 

While generally vaccines that protect against the symptoms of a disease tend to do even better at preventing more serious cases, FDA wanted to be sure the clinical trial data included direct evidence that the vaccine could help alleviate the pandemic’s hospitalizations and deaths.

The clinical trial saw 30 severe cases, far more than the FDA’s requirement of five. All of these cases occurred in the placebo arm, suggesting the vaccine is effective at staving off severe disease. Nine of those severe cases resulted in hospitalization. One 54-year-old with diabetes who received a placebo died of COVID-19.

The clinical trial enrolled 6,742 people with co-morbid conditions that can exacerbate COVID-19 disease, like chronic lung disease, obesity, diabetes, liver disease and HIV infection. The vaccine was found to be 96 percent effective in this clinical trial subgroup.

But important questions will have to be answered in further studies, like how long protection lasts and how well the vaccine prevents transmission. 

Side effects like fever, chills, headache, fatigue, muscle pain, joint pain, and nausea — signs the body is mounting an immune response — were more common in people of all ages after the second dose. Among people older than 64, the most common side effects were fatigue (58.4 percent of people getting the vaccine); headache (46 percent of those getting the vaccine); muscle pain (47 percent of those getting the vaccine) and joint pain (35 percent of those getting the vaccine).

The frequency of serious health complications was the same among people getting the vaccine and getting the placebo, occurring in about 1 percent of volunteers. 

Questions have also been raised about whether two-dose vaccines could be effective after one dose. The Moderna vaccine was anywhere from 50 percent effective to 95 percent effective in the days following the first dose, with efficacy increasing over time. But after one dose, protection against severe cases showed just 42.6 percent efficacy. 

The efficacy of one dose also could be observed only during a short window, since all participants who got the first dose got a second booster shot after 28 days.

On Thursday, the expert advisors will vote on whether FDA should authorize the vaccine. The vote is non-binding but highly influential. 

The FDA specified in its briefing document it has not yet independently verified the safety and efficacy data. That number-crunching and analysis will continue this week. 

If the Moderna/National Institutes of Health vaccine receives emergency use authorization, a combined 6 million doses would land at 3,285 locations within three days, according to Gustave Perna, the co-leader of Operation Warp Speed, the Trump administration’s COVID-19 vaccine and therapeutics initiative. 

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