Moderna announced that its COVID-19 vaccine candidate is 94.5 percent effective at protecting people from infection, compared to patients who received a placebo saline shot, according to an interim analysis of 95 participants the company released today (November 16).

“These are obviously very exciting results,” Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases, tells CNN, noting he expects the first vaccinations to begin toward the end of December. “It’s just as good as it gets—94.5 percent is truly outstanding.”

The results put Moderna’s vaccine on par with competitor Pfizer’s COVID-19 vaccine, which was found to be 90 percent effective in a preliminary analysis of 94 participants. Both companies are expected to seek authorization for emergency use in the US and from other global regulators in the coming weeks. The European Medicines Agency announced today that it has begun...

Both vaccines use mRNA to instruct cells to create many copies of a piece of the SARS-CoV-2 virus, causing the immune system to be prepared to attack the virus should it try to invade. Although there are other vaccines in development that use this technology, none have been approved yet.

As mRNA can quickly degrade in warm temperatures, vaccine storage presents a serious practical challenge. While Pfizer’s vaccine must be stored at –70 °C, Moderna’s can be kept at –20 °C. Moderna also said today that once thawed, its vaccine can remain stable for a month at 2–8 °C. 

“The fact that two different vaccines made by two different companies with two different kinds of structures, in a new messenger RNA concept, both worked so effectively confirms the concept once and for all that this is a viable strategy not only for COVID but for future infectious disease threats,” Barry Bloom, a public health professor at Harvard University, tells The New York Times.

It’s unclear exactly how many of the trial’s 30,000 participants, who received either two doses of the vaccine or the placebo, have contracted COVID-19. The interim analysis includes 95 confirmed cases—five who had been given the vaccine and 90 who received the placebo. Among this group, 11—all in the placebo group—developed severe COVID-19. 

“It was one of the greatest moments in my life and my career. It is absolutely amazing to be able to develop this vaccine and see the ability to prevent symptomatic disease with such high efficacy,” Tal Zaks, Moderna’s chief medical officer, tells CNN.

Like the Pfizer vaccine, Moderna’s reportedly does not have any serious side effects, but a small percentage of participants in the study experienced symptoms such as body aches and headaches. Pfizer did not release data on the vaccine’s performance to prevent severe cases.

Both companies announced their findings in press releases, not in peer-reviewed journals, and neither company provided the detailed data that would allow outside experts to evaluate their claims. As the studies continue, the figures on the vaccines’ efficacy may change. It is also unclear how long the immunity provided by the vaccines will last. Moderna and Pfizer conducted their trials using slightly different protocols. While participants in the Moderna trial needed to display at least two symptoms of disease in addition to a positive test for the virus to be officially counted as a COVID-19 case, the Pfizer trial required only one symptom and a positive test. Pfizer started counting cases seven days after the second injection of the vaccine, and Moderna waited 14 days.

Moderna has a $1.525 billion contract to provide the US with 100 million doses of the vaccine through Operation Warp Speed, with an option to purchase an additional 400 million doses.

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