A pharmacist dilutes the Pfizer COVID-19 vaccine while preparing it to administer to staff and residents at the Goodwin House Bailey’s Crossroads, a senior living community in Falls Church, Virginia, on December 30, 2020.Brendan Smialowski | AFP | Getty ImagesThe Covid-19 vaccine appears to cause severe allergic reactions at a significantly higher rate than other vaccines among the first wave of Americans to receive the life-saving immunizations, the U.S. Centers for Disease Control and Prevention said Wednesday.Though still rare, the CDC said there were 21 cases of anaphylaxis — a severe and life-threatening allergic reaction that occurs rarely after vaccination — out of the nearly 1.9 million people who received their first shot of Pfizer’s Covid-19 vaccine in mid- to-late December, according to a study published in the CDC’s Morbidity and Mortality Weekly Report on Wednesday.That would mean roughly 11 people out of every million vaccinated would likely experience anaphylaxis, according to CDC data — roughly 10 times higher than the flu vaccine.Dr. Nancy Messonnier, the director of the CDC’s National Center for Immunization and Respiratory Diseases, told reporters on a conference call the inoculations were safe for public use and the severe allergic reactions — though higher — were still considered rare.”The anaphylaxis rate for Covid-19 vaccines may seem high compared to flu vaccines, but I want to reassure you that this is still a rare outcome,” Messonnier said in the call before the study was released. She added that the data applies to both Pfizer and Moderna’s vaccines, which use similar mRNA technology.Of the 21 people who experienced the severe allergic reactions, 17 of them had a documented history of allergies or allergic reactions. Seven of those people had a history of anaphylaxis, the study found.Most people experienced symptoms within 15 minutes after they were given the shot, although anaphylaxis can occur hours after someone is vaccinated, the CDC said. Among the 20 people with follow-up information available, all had recovered or been discharged home, the study found.Most people experienced symptoms within 15 minutes after they were given the shot, although anaphylaxis can occur hours after someone is vaccinated, the CDC said. Among the 20 people with follow-up information available, all had recovered or been discharged home, the study found.”Of course, we all would hope that any vaccine would have zero adverse events, but even at 11 cases per million doses administered, it’s a very safe vaccine,” Messonnier said. She added that there are “tremendous efforts” underway to try to determine exactly what is causing the severe allergic reactions.The coronavirus is killing an average of 2,670 people in the U.S. every day, according to a CNBC analysis of data compiled by Johns Hopkins University, making the vaccine a “good value proposition,” Messonnier said.According to interim guidance from the CDC’s Advisory Committee on Immunization Practices, last updated in December, everyone should be observed for 15 minutes following their vaccination to ensure they don’t develop symptoms. People with a history of anaphylaxis should be observed for 30 minutes, the committee advised.The committee also suggested that people who develop anaphylaxis following their first dose shouldn’t be given a second dose since both drugs require two shots spaced weeks apart for full effectiveness. The CDC’s study said that every vaccination site should have supplies like epinephrine ready to treat patients who might develop the severe reactions.”Fortunately, we know how to treat anaphylaxis, and we’ve put provisions in place to ensure that at immunization sites, the folks administering the vaccine are ready to treat anaphylaxis,” Messonnier said.