Public Health Watch: Moderna Vaccine May Cause More Reactions, Higher Antibody Response


Study comparing mRNA shots finds variability in response, though both generally safe and effective.

moderna vaccine

All mRNA COVID-19 vaccines are not created equal—at least according to an analysis published on August 16 in JAMA Internal Medicine.

If the assessment of vaccine response in 954 health care workers in the Johns Hopkins Health System is accurate, those given the Moderna shot are nearly 150% more likely to develop “clinically significant symptoms” following receipt of the second dose compared with recipients of the Pfizer jab. Clinically significant symptoms, as defined by the authors, included fatigue, fever, and chills. Moderna recipients were also 83% more likely to develop these symptoms following their first dose, compared with those given the Pfizer vaccine.

Still, overall, less than half of participating health care workers (43%) developed these symptoms after receiving the second dose of either vaccine. Only 5% had them following their first shot, according to the researchers.

Conversely, those given the Moderna vaccine may also have more robust antibody responses, the researchers said.

“These vaccines can elicit greater local and systemic reactions in persons with prior SARS-CoV-2 infection,” they wrote. “Whether symptoms following vaccination are associated with effectiveness is unknown, and, therefore, anxiety can arise in persons who did not develop a reaction following vaccination.”

Indeed, prior history of SARS-CoV-2 infection was associated with a nearly five-fold higher risk for clinically significant symptoms following their first dose of either vaccine—but not the second. However, those with a prior infection who received the vaccine generally had a more robust antibody response after getting the shot, according to the researchers.

In addition, although 953 of 954 study participants developed spike IgG antibodies 14 or more days following dose 2—with the lone exception being 1 who was taking immunosuppressant medication at the time—reporting clinically significant symptoms was associated with higher median IgG measurements. Indeed, vaccine recipients reporting clinically significant symptoms following inoculation were about 5% more likely to have higher IgG levels, while those given the Moderna shot were nearly 10% more likely to do so, the researchers noted.

“Spike IgG antibody measurements were higher in health care workers who received the Moderna vaccine, had prior SARS-CoV-2 infection, and reported clinically significant reactions,” they wrote. “The role of higher antibody levels in preventing COVID-19 and providing lasting immunity remains unknown, however. Overall, the findings suggest that regardless of vaccine reactions or prior SARS-CoV-2 infection, either spike mRNA vaccine will provide a robust spike antibody response.”

Which, in the end, is all that really matters.

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