No COVID-19 Vaccines Safety Surprises
January 27, 2021 – The United States is almost 6 weeks into its historic campaign to vaccinate Americans against the virus that causes COVID-19, and so far the two vaccines in use appear remarkably low risk, according to new data presented today at a meeting of vaccine experts advising the CDC.
With 23.5 million doses of Pfizer and Moderna vaccines now administered, there have been very few serious side effects. Additionally, deaths reported after people received the vaccine do not appear to be related.
The most common symptoms reported after vaccination were pain at the point of vaccination, fatigue, headache and muscle pain. These were more frequent after the second dose. Additionally, around 1 in 4 people reported fever and chills after the second injection.
“Overall, I found it to be very reassuring,” said William Schaffner, MD, an infectious disease expert at Vanderbilt University School of Medicine in Nashville who listened to the presentations.
The CDC collects safety information through several channels. These include a new smartphone-based app called V-Safe, which collects daily information about people who have been vaccinated; the Federal Vaccine Adverse Event Reporting System, or VAERS, which accepts reports from anyone; and Vaccine Safety Datalink, which is a collaboration between the CDC and nine major hospital systems. There’s also CISA, the Clinical Immunization Safety Assessment Project, a collaboration between CDC and vaccine safety experts.
After studying these systems, experts at the head of the safety committee of the CDC Advisory Committee on Immunization Practices say few serious side effects have been reported.
Very rarely, severe allergic reactions – called anaphylaxis – have occurred after vaccination. To date, 50 of these cases have been reported after the Pfizer vaccine and 21 cases after the Moderna vaccine. Almost all – 94% of cases of anaphylaxis after Pfizer vaccines and 100% of those after Moderna’s vaccine – have been in women, although it is not known why.
This translates into a rate of about five cases of anaphylaxis for every million doses of Pfizer vaccine and about three for every million doses of Moderna vaccine. Most of these occur within 15 minutes of receiving a dose of the vaccine, with a report as long as 20 hours after the injection.
The CDC suspects that these may be related to an ingredient called polyethylene glycol or PEG. PEG is part of the particles that slip vaccine mRNA into cells with instructions to make the virus spike protein. The cells then express these peaks on their surfaces so that the immune system can learn to recognize them and defend against them. PEG is a common ingredient in many drugs and sometimes triggers anaphylaxis.
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