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Serious Adverse Events After Updated COVID-19 Booster Shots Are Rare


Reports of serious adverse events after administration of the updated COVID-19 booster shots were rare, according to a new study from experts at the Centers for Disease Control and Prevention and the Food and Drug Administration.

The agencies found “no unusual or unexpected patterns of adverse events” after vaccination with the shots from Moderna and Pfizer, which are authorized for children as young as 5 years old, according to a summary of the study.

The research, which was published by the CDC on Thursday, looked at data collected during the seven weeks after the updated shots were authorized in August. More than 22 million booster shots were administered in that timeframe, which is equivalent to about 6% of the U.S. population.

Researchers at the agencies looked at reports to two post-vaccination monitoring systems and found that the vast majority of the reports were not serious.

The Vaccine Adverse Event Reporting System received over 5,500 reports of adverse events after vaccination with the updated shot. Of those, more than 95% were not serious and over 4% were serious events.

Serious events included five cases of myocarditis, which is inflammation of the heart muscle and has been associated with messenger RNA COVID-19 vaccine in rare cases. The age range of those who reportedly experienced myocarditis was 12-78 years old.

Health care providers and patients “can be reassured” that the safety data is similar to what was seen after the original COVID-19 shots, according to the report. Common mild reactions included reports of headaches, fever, fatigue, injection-site pain and chills.

The findings are also “generally consistent with those from safety data from preauthorization clinical trials of a BA.1 Omicron bivalent booster vaccination,” which was the data that federal authorities used to authorize the updated shots that target omicron subvariants BA.4 and BA.5.

“CDC and FDA will continue to monitor vaccine safety and will provide updates as needed to help guide COVID-19 vaccination recommendations,” the study stated.

The report comes after a pair of studies raised questions about whether the updated COVID-19 booster shots will be more effective than another dose of the original vaccine.

The first study concluded that there was “no significant difference” in the neutralization of any coronavirus variants in people who got a fourth dose of the original vaccine compared to the updated shot. The other study found a “modest and nonsignificant” improvement in BA.5-fighting antibodies from the updated booster shot compared to the original formula.

Further, amid waning immunity and incoming colder weather, experts are concerned that not enough Americans will get the updated shots to make a substantial difference in the potential COVID-19 wave expected in the fall and into the winter.



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