Categories: Vaccine

Serious side effects of Moderna’s Covid-19 vaccine

Discover the serious side effects of Moderna’s Covid-19 vaccine.

High fever and fainting are some of the side effects of this vaccine, which is still in clinical trials

Several people who have voluntarily participated in clinical trials of the vaccine being developed by the Moderna Therapeutic company against Covid-19, the disease caused by the new coronavirus, have warned that it causes high fever and fainting.

According to an article published in ‘Stat’, Ian Haydon, a 29-year-old from Seattle (United States) has participated in these studies and has even volunteered to expose himself to the new coronavirus if a group of scientists wants to test whether their vaccine is effective.


For now, Haydon has participated in the Modern company and, as he explained, within 12 hours of receiving the second dose he developed a high fever and, after being discharged from the emergency services, he fainted when he arrived at his house, although he recovered the next day.

That there is no “general antagonism towards vaccines”

«I understand that sharing the story is going to be scary for some people, but I hope it does not generate any kind of general antagonism towards vaccines or even this vaccine, although I hope that my story counteracts the desperation that some people have for launch a vaccine on the market, regardless of its consequences, “he explained.

And, as reported, the objective of the clinical trial, in phase 1, is to find the correct dose of the vaccine that allows the body to generate antibodies but without causing side effects. “Vaccines have to develop at the speed they require. Stories like the one that happened to me are important because they shape the approval process, “he said.

In Moderna’s study of 45 people, four participants experienced what is known as ‘Grade 3’ adverse events – side effects that are serious or medically significant but not immediately life-threatening.


Neither the company nor the National Institute of Allergy and Infectious Diseases, which is conducting the trial, have previously detailed the nature of those incidents, although the company has disclosed that three participants, likely including Haydon, received the highest dose of the vaccine that was tested and they experienced reactions that involved their entire body. A fourth volunteer received a lower dose and had a rash at the injection site.

A severe anaphylactic shock

Haydon, a communications manager for a university, first learned about the study, which was running in Seattle, from a friend who sent him a link. He, along with thousands of other people, applied to participate and was called 11 days after he applied.

To participate, she had to undergo a physical exam and fill out a 20-page consent form. In addition, they informed him that the vaccine could cause severe anaphylactic shock, and there was no way to predict exactly how his immune system would respond to the new vaccine.

Haydon had studied research on other Modern experimental vaccines, which work through an entirely new technology that uses messenger RNA, the body’s key envoy of genetic information inside cells, and though they appeared relatively safe. During the physical exam, the researchers drew blood from him, and a week later, he received his first dose.


They gave him a paper log to record any symptoms, a digital thermometer, and a small ruler to measure any reactions at the injection site. The next day, he felt pain in his arm, “like a punch” and had trouble lifting it for a few days. This pain was more pronounced in the second dose, with which his fever rose, he vomited and passed out.

Given the stakes with a Covid-19 vaccine, the side effects described in Moderna’s launch would likely be considered acceptable, even if they were seen in future studies. Severe effects were only seen in high doses that are not being carried forward. The other vaccine for which preliminary data is available caused fever in almost half of the recipients.

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