Moderna says its COVID-19 vaccine is nearly 95 percent effective

Two leading candidates have now reported preliminary data showing success in preventing illness

older man wearing a mask receiving a shot

Tony Potts, a 69-year-old participant in Moderna’s COVID-19 vaccine clinical trial, receives the company’s vaccine in August.

Paul Hennessy/NurPhoto/Getty Images

Editor’s note: This story was updated to include results of a fuller analysis released by Moderna on November 30.

On the heels of the preliminary success of one COVID-19 vaccine in the United States, another leading vaccine candidate is showing promise. Preliminary results indicate that Moderna’s coronavirus vaccine is nearly 95 percent effective in preventing sickness, including severe cases of the disease, the biotechnology company announced November 16.

 “This is a pivotal moment in the development of our COVID-19 vaccine candidate,” Moderna CEO Stéphane Bancel said in a news release. The results are the “first clinical validation that our vaccine can prevent COVID-19 disease.”

A fuller analysis released November 30 supports those findings. Of 196 COVID-19 cases in the study, 185 were in the placebo group, making the vaccine 94.1 percent effective. The vaccine completely prevented severe disease. All 30 severe cases and one death among study participants were people who had gotten the placebo. Moderna said in a news release that it would apply for emergency use authorization November 30, and the U.S. Food and Drug Administration has told the company to expect a hearing of its vaccine committee on December 17.

Similarly, global pharmaceutical company Pfizer and German biotech company BioNTech  originally announced November 9 that their coronavirus vaccine was more than 90 percent effective in preventing people from getting sick from the virus (SN: 11/9/20), but found upon reviewing the full results that the vaccine’s effectiveness was actually about 95 percent (SN: 11/18/20). An FDA hearing to consider Pfizer’s emergency use authorization request is set for December 10.

Moderna’s earlier preliminary results were based on an analysis of 95 coronavirus cases that have occurred so far during the company’s Phase III clinical trial of the vaccine. Researchers began counting who fell ill at least two weeks after participants received a second vaccine dose. Of the cases, 90 were in people who received a placebo and five were in the vaccinated group, making the vaccine 94.5 percent effective. The data are preliminary and have yet to be peer reviewed by other scientists.

The FDA recommends that COVID-19 vaccines have at least 50 percent efficacy, meaning a vaccine should reduce COVID-19 cases in vaccinated people compared with a placebo by half (SN: 10/4/20). Both Moderna and Pfizer’s clinical trials are ongoing so the final efficacy of the vaccines could change.

It’s unclear how well Moderna’s vaccine performs in different age or racial groups, though the results do include some older participants as well as people of different racial backgrounds. Of those who got sick, 15 of the 95 cases were in people older than 65. Another 20 cases were in Hispanic, Black, Asian or multiracial participants — groups that have been disproportionately hard-hit during the pandemic (SN: 4/10/20)

Importantly, the new results hint that the vaccine may prevent people from developing severe disease if they do get infected with the virus. In the clinical trial so far, 11 people have fallen severely ill, all of whom had received the placebo.

It’s encouraging to see early results that suggest that the vaccine can decrease disease severity, says Nina Luning Prak, an immunologist at the University of Pennsylvania. “That’s still a small number, but it’s 11 out of 11 versus zero on the other side.” 

Moderna, based in Cambridge, Mass., and the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Md., worked together to develop the vaccine. Previous work showed that the vaccine sparks an immune response in people who receive it (SN: 5/18/20).

By October 22, 30,000 participants had been enrolled in the company’s late-stage clinical trial, though thousands of people still needed to receive both shots, which are given one month apart.

Previous studies have shown that the vaccine is safe. People in the trial have reported mild to moderate side effects after the second injection, including fatigue, joint pain and headache. There have not been any severe reactions. Moderna plans to follow participants for two years to more completely monitor the vaccine’s safety.

Both Moderna and Pfizer’s vaccines rely on messenger RNA, or mRNA, a genetic molecule that cellular machinery “reads” to build proteins inside cells. For these vaccines, the mRNA contains instructions for building the coronavirus’ spike protein, which helps the virus enter human cells.

The vaccines induce human cells to make the spike protein, and the immune system then makes antibodies to latch onto the spike proteins. Those vaccine-stimulated antibodies may prevent the real virus from infecting healthy cells in the future.

No vaccine using such mRNA technology has ever been used in people. If such vaccines prove successful, that could expedite the vaccine-making process. “That’s one of the strengths of the platform,” Luning Prak says. “Within a matter of essentially minutes, you could basically design a vaccine.” That’s because these vaccines don’t rely on laboratory-grown cells to produce millions of doses like other types of vaccines do. All researchers need is the genetic code for a particular viral protein, such as the spike protein. Although choosing the right protein out of many possibilities to generate the best immune response may still prove tricky, mRNA vaccines “clearly have promise,” she says. 

Pfizer and BioNTech’s vaccine must be kept frozen at an ultracold –70° Celsius (–94° Fahrenheit), making its distribution potentially difficult. Moderna’s vaccine, however, can remain stable at refrigerated temperatures — between 2° to 8° C or 36° to 46° F — for 30 days, the company said in the Nov. 16 news release. That could help allocate COVID-19 vaccines in areas without easy access to dry ice or specialized freezers needed for Pfizer’s vaccine.  

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