Skip to Main Content

And now there are two.

The Food and Drug Administration on Friday issued an emergency authorization for a Covid-19 vaccine developed by Moderna, the second such vaccine to be cleared in the United States. Inoculations should begin within days, as was the case following last week’s authorization of the Covid-19 vaccine developed by Pfizer and its partner BioNTech.


The decision, while widely expected, will help fuel the historic effort to rein in a pandemic that has so far infected an estimated 17 million people and killed more than 300,000 in the United States. Its authorization comes at a time when Covid-19 hospitalizations are hitting record highs, and the number of overall cases continues to soar.

“With the availability of two vaccines now for the prevention of COVID-19, the FDA has taken another crucial step in the fight against this global pandemic that is causing vast numbers of hospitalizations and deaths in the United States each day,” said FDA Commissioner Stephen Hahn in a statement.

The authorization also comes amid a handful of reports of possible allergic reactions — including cases of a severe allergic reaction, anaphylaxis — among people in the United States who have received the Pfizer vaccine. Last week, two nurses in the United Kingdom with a history of severe allergies developed anaphylaxis after being vaccinated.


Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, told reporters Friday night that “out of caution” the agency recommends that people who have severe allergic reactions to any components of the two vaccines should not be vaccinated with either of these products.

Both vaccines are made using similar approaches, injecting messenger RNA encased in lipid nanoparticles into an arm muscle; the mRNA is in effect a recipe that instructs cells how to make the SARS-CoV-2 virus’ spike protein; its presence teaches the immune system to recognize the virus as an invader.

Marks said investigations are underway to try to pinpoint what in the Pfizer vaccine appears to be triggering allergic reactions in a small number of people who receive it, with attention currently focusing on a compound called polyethylene glycol, or PEG, which is a component in other injectable medicines. Marks said it was known that PEG can be associated with allergic reactions in rare cases, but it may be that these events are not as rare as were earlier thought.

“That could be a culprit here,” he said. Marks noted that while it’s not known if the Moderna vaccine will trigger allergic reactions, the FDA and the Centers for Disease Control and Prevention — which are collaborating on surveillance for side effects induced by the vaccine — will be on the lookout for any such events.

Even with two vaccines cleared for use, however, initial supplies will remain tight. The United States has agreed to purchase 200 million doses of the Moderna vaccine, on top of the 100 million doses it has agreed to purchase of the Pfizer/BioNTech vaccine — and it is reportedly in negotiations to purchase more. But it will take months for the vaccine makers to scale up manufacturing. And because each vaccine requires the administration of two doses, the existing agreements will cover less than half the U.S. population.

For now, the vaccines will continue to be used primarily in two groups most at risk of getting infected or developing severe disease: health care providers and residents and staff of long-term care facilities. Moderna’s vaccine was authorized for individuals 18 and older, while the Pfizer/BioNTech vaccine was authorized for individuals 16 and older.

In clinical trials, Moderna’s vaccine was 94% effective in decreasing symptomatic Covid-19 infections, while also preventing more severe forms of the disease. Its effectiveness was roughly in line with the Pfizer/BioNTech vaccine.

The vaccine caused side effects including pain at the injection site, tiredness, headache, muscle pain, chills, joint pain, swollen lymph nodes in the same arm as the injection, nausea and vomiting, and fever. Side effects typically lasted several days.

Marks said that the side effect profiles of the two vaccines are “reasonably similar” and that he did not expect side effects to slow the use of the Moderna vaccine.

“I think that ultimately, if these [side effects] are managed well, if we communicate the expectations well, I think particularly among those who are eager to get back to a normal life, which I think that includes many of us, there will be reasonable uptake of this [vaccine] and we’ll continue to communicate about these side effects to help people be prepared to know what to expect,” he said.

The Moderna vaccine may also be easier to distribute, because it can be transported for longer in normal freezers, and kept longer at normal refrigerator temperatures.

The FDA’s decision marks the first authorization for Moderna’s vaccine in any country, though the company has submitted its data to regulators in the U.K. and Europe. It also marks the first clearance of any drug or vaccine developed by Moderna, which was founded in 2010 to develop drugs and vaccines based on mRNA technology.

A number of other Covid-19 vaccine candidates are still in clinical trials, including those being developed by Johnson & Johnson, which is developing the only single-dose vaccine, AstraZeneca, and Novavax.

Helen Branswell contributed reporting.

This story has been updated with details from an FDA media briefing.

Comments are closed.