As of January 20, 2021, a total of 24,135,690 cases of coronavirus disease 2019 (COVID-19) and 400,306 associated deaths had been reported in the United States. (

The Centers for Disease Control and Prevention said in its Morbidity and Mortality Weekly Report that 0.03%, or 1,266, of the more than 4 million people who have received the first dose of Moderna's COVID-19 vaccine experienced adverse events. Of the recipients with side effects, 108 were identified for further review as severe allergic reactions, including anaphylaxis – a life-threatening allergic reaction that the CDC says can occur after a vaccination, although rarely. It typically occurs within minutes to hours.

LESS THAN 1% OF PEOPLE who have received Moderna's coronavirus vaccine have experienced adverse side effects.

Among the 108 instances of allergic reaction, 10 were determined to be anaphylaxis, amounting to a rate of 2.5 anaphylaxis cases per 1 million vaccine doses administered. Of the 10, it included nine people who had a previous history of anaphylaxis. Follow-up information was available for eight people, all of whom had recovered from their reactions and been sent home. Of the remaining people who experienced adverse side effects, 47 were determined to be non-anaphylaxis allergic reactions, another 47 were considered to be non-allergic adverse events and four cases were undetermined.

The two-dose COVID-19 vaccine developed by Moderna received emergency use authorization in the U.S. in December and has been deemed 94.1% effective in preventing COVID-19, which has infected more than 24.6 million people in the country and killed more than 411,400.

An earlier analysis of the incidence rate of anaphylaxis after receiving the first dose of the coronavirus vaccine developed by Pfizer and BioNTech revealed it was at a rate of 11.1 cases per 1 million doses.

The CDC and FDA identified reports of suspected anaphylaxis in VAERS, the national passive surveillance (i.e., spontaneous reporting) system for monitoring adverse events after immunization. CDC physicians screened VAERS reports describing suspected severe allergic reactions and anaphylaxis and applied Brighton Collaboration case definition criteria for anaphylaxis*. After initial screening, reports with sufficient evidence to suggest anaphylaxis were followed up by collecting information from medical records and through direct outreach to health care facilities and treating health care providers, and, in some cases, vaccine recipients. Physician reviewers classified all initially identified case reports as anaphylaxis or not anaphylaxis and used clinical judgment to further categorize reports that were considered not anaphylaxis as nonanaphylaxis allergic reactions or nonallergic adverse events.

Nonallergic adverse events, mostly vasovagal (e.g., fainting or the sensation of fainting) or suspected anxiety-related, were excluded from the final analyses. Anaphylaxis and nonanaphylaxis allergic reaction cases with symptom onset occurring later than the day after vaccination (i.e., outside the 0–1-day risk window) were also excluded because of the difficulty in clearly attributing allergic reactions with onset later than this to vaccination.

In nine of 10 cases of anaphylaxis after receipt of Moderna COVID-19 vaccine, patients had symptom onset within 30 minutes of vaccination, and nine anaphylaxis patients also had a history of allergies or allergic reactions, including some with previous anaphylaxis events; up to 30% of persons in the general population might have some type of allergy or history of allergic reactions.

The clinical and epidemiologic characteristics of anaphylaxis case reports after receipt of Moderna COVID-19 vaccine are similar to those reported after receipt of the Pfizer-BioNTech COVID-19 vaccine. For both vaccines, symptom onset after vaccination occurred quickly, usually within minutes. A strong female predominance of anaphylaxis case reports exists for both vaccines. Finally, many persons experiencing anaphylaxis after receiving either vaccine had a history of allergies or allergic reactions, with several having experienced an anaphylaxis episode in the past. Similar patient characteristics in case reports of nonanaphylaxis allergic reactions were observed among the two vaccines.

FACT: We have COVID-19 vaccines available now because science and health experts responded swiftly to a deadly public health crisis

Myths and fears: Many people have voiced concerns about how quickly the vaccines have become available, how short the testing process was, or how political the whole vaccine production effort has gotten because of the national election.

There are claims that it was rushed, or that “corners were cut” in the clinical trials or the government’s safety review and approval process.

The bottom line: The entire process went faster than usual for explainable reasons, but still followed the usual steps for testing and review. The most important reasons for speed: modern scientific tools are faster than old ones, and there was a worldwide effort to reduce or remove the usual barriers and delays in vaccine research, production and distribution. A large number of ordinary people volunteered for clinical trials of the vaccines, which meant we got the answers to key questions about safety and protection quickly.

The vaccines still received independent review and approval, under emergency rules put in place before this pandemic for situations where the public’s health is at serious and immediate risk, as it is now.

The effort started with rapid research on the genetics of the coronavirus, starting in January. Scientific tools have made it possible to “read” the genetic material of a virus in mere days, where it once took months. Meanwhile, scientists and vaccine makers had already been working for years to develop a “platform” approach to making vaccines against new viruses. This “platform” uses messenger RNA (mRNA) as the delivery agent to teach the body how to recognize and fight a new virus.

The first vaccines to reach the market use this “platform” strategy. The other vaccines that are still being studied are based on vaccine strategies that have been used in the past, but these take longer. Part of the delay in studying a new vaccine is the time it takes to design a high quality and safe clinical trial. For COVID-19, international organizations came together to agree on a study outline and goals.

Another big difference is that governments agreed to pay companies to produce large amounts of their vaccines in advance, even while trials were testing how well the vaccine actually worked in people. If those clinical trials showed a vaccine didn’t work, or had unacceptable side effects, it would be thrown out – but the company wouldn’t lose money. On the other hand, if the trials showed a vaccine worked and was safe, the companies would be ready to ship it out – which is what’s happening now.

Another source of speed: The fact that the pandemic was so out of control in the U.S. and other countries this summer and fall, when the clinical trials were going on. Because the people who volunteered to get the vaccine had a high chance of being exposed to the virus in their everyday lives, researchers could see within months how many of the ones who got actual vaccines got sick with COVID-19, compared with the people in the groups that got the placebos.

The approval process through the FDA had an independent panel of experts look at the data from the studies, and ask tough questions of the vaccine makers before voting to approve it on an emergency basis. The FDA is also requiring the companies to track what happens to people who took part in its studies, and the CDC will monitor what happens to people who get the vaccine outside the studies.

FACT: The mRNA-based vaccines do not change a person’s DNA