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The Moderna Covid-19 vaccine, like the one made by Pfizer and BioNTech, appears to induce rare anaphylactic reactions in a small number of people who receive the vaccine, new data from the Centers for Disease Control and Prevention suggest.

As of Jan. 19, there have been 15 confirmed cases of anaphylaxis after receipt of Moderna’s vaccine and 45 confirmed cases of anaphylaxis after receipt of the Pfizer vaccine, the CDC said in a statement to STAT. That works out to a rate of 2.1 cases per million doses of the Moderna vaccine and 6.2 cases per million doses of the Pfizer, according to the agency.

Anaphylaxis is a severe allergic reaction that can be life-threatening if not treated quickly.

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“Early monitoring of both the Moderna and the Pfizer-BioNTech Covid-19 vaccines indicate that anaphylaxis following vaccination is a rare event, and although anaphylaxis is serious, it occurs shortly after vaccination (usually within minutes), is readily diagnosed, and effective treatments are available,” the agency said via email.

It noted that the rates at which anaphylaxis is reported following vaccination is likely to change as more vaccine doses are given. In fact, they already have. The first report on U.S. cases of anaphylaxis following administration of the Pfizer vaccine suggested it occurred at a rate of 11.1 cases per million doses given.

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In a report published Friday on anaphylaxis cases among people who received the Moderna vaccine between Dec. 21 and Jan. 10, the CDC detailed 10 cases, all of which occurred in women. During the period of study, more than 4 million doses of the Moderna vaccine were administered.

In Friday’s report, six of the 10 people who developed anaphylaxis were hospitalized and four of them needed to be intubated to assist their breathing. None of the people died, the CDC reported. To date there have been no reports of fatal cases of anaphylaxis associated with Covid vaccines in the United States.

All 10 of the people who developed anaphylaxis were given epinephrine, the drug in EpiPens that is used to combat severe allergic reactions. The CDC has said that those administering Covid vaccines need to be equipped to treat anaphylaxis, including having epinephrine injections on hand.

Anaphylaxis occurred quickly in the people affected, with the median time to the start of symptoms being 7.5 minutes. People who receive Covid-19 vaccines are supposed to be monitored for 15 minutes after the injection, with that period extended to 30 minutes for people with a history of severe allergies or anaphylaxis.

Nine of the 10 people had a history of allergies and five of them had previously experienced an anaphylactic reaction.

This story has been updated with additional data and comment from the CDC. 

  • How does this rate of anaphylaxis compare to other routine vaccinations? If higher than say Shingrex or Pneumococall, could it be related to mRNA technology or an ingredient in the vaccine

  • I had my Moderna Covid-19 vaccine shot Jan 14th with very few side effects immediately following the shot aside from some pain in my arm and a little fatigue.
    A week later, the following Friday morning I developed an itchy, hot, red spot on my arm at the inject site. I took a Benadryl Friday night and put some Cortisone cream and Neosporin pain relief on the spot. Saturday morning I took a Claritin and continued to apply the ointments to the spot throughout the day. By Sunday the spot was clearing up. Today (Monday) it is only very very faintly visible and does not itch and is not hot anymore. It sounds like this is more common than reported, why is that?

  • I had same thing, on day 7 after my shot my entire upper arm was hot and swollen and RED. I went to doctor and they told me to take Benadryl and put ice on it.
    Now on day 10 after and its still red, but not hot anymore. Benadryl seems to be trying to help. I am in Alabama and several cases like this have happened after apparently.

    • The CDC and News should be all over these types of results with a reporting center that collects info for at least 30 days. Where is the transparency ? Especially bc these vaccines were developed without regard to normal guidelines and trails with most health conditions represented.

    • I had the exact same delayed reaction. It happened on day 9 after my first dose of the Pfizer vaccine. I developed a hot itchy swollen rash just below the vaccine injection site on my right upper arm. I took an antihistamine, iced it, and used cortisone cream and it seems to be dissipating but is still hot to the touch. They were sending check ins through vsafe for the first week but now at day 9, nobody is asking about side effects and I don’t know how to report it. I am a healthcare professional. They need to be following people for much longer than one week.

  • I had the first Moderna vaccine on 1/12. Since then I have developed a rash on the vaccine site that is spreading.

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