Now that the U.S. has shifted its focus onto the rollout of the booster shots, many people are wary of the possible side effects of the additional doses, considering that the main series of vaccines caused some form of discomfort to their bodies upon administration. Clinical trials showed that the common side effects of Pfizer’s and Moderna’s boosters are actually almost the same, with most of them ranging from mild to moderate and all of them being self-limiting.

Side Effects Of Pfizer’s Third Dose

Prior to gaining the approval of the U.S. Food and Drug Administration for its booster’s public release in September, Pfizer and BioNTech conducted clinical trials on the effects of their booster shot to the human body. Based on the analysis of data from participants who enrolled in the trials, the most common side effect of the booster was pain at the injection site. This side effect was reported by about 83% of the participants.

Another very common side effect in Pfizer booster recipients was fatigue, which was reported by 63.7% of the participants. This was followed by headache at 48.4%. The other side effects that were reported by fewer participants were muscle pain and chills. Meanwhile, the least common side effects reported in the trials were joint pain, diarrhea, vomiting and fever.

Pfizer’s trials also found that adults aged 65 and beyond were less likely to experience the flu-like symptoms and side effects after receiving the booster shot compared to individuals aged 18 to 55. However, Mayo Clinic’s COVID-19 Vaccine Allocation and Distribution Workgroup cochair Melanie Swift, MD, told AARP that this is not at all surprising since the side effects serve as an indication of the immune system’s reaction to the vaccine. Older adults have weaker and less robust immune systems, so their bodies tend to not elicit an immune response.

Side Effects Of Moderna’s Third Dose

Just like Pfizer, Moderna also conducted trials to determine the common side effects of its booster shot prior to its authorization for public rollout by the FDA in October. And based on the data it forwarded to the federal agency, Moderna’s third dose also causes similar side effects or symptoms to its recipients, with pain at the injection site being the most commonly reported by participants at 76%.

The second and third most common symptoms in Moderna booster recipients were fatigue and muscle pain at 47.4% each. They were followed by headache at 42.1% and joint pain at 39.5%. Other side effects reported by participants were chills, fever and nausea. No safety concerns were reported during the trials and older adults (aged 65 and above) also experienced less symptoms compared to people aged 18 to 64.

What The CDC Is Saying

The side effects of the mRNA COVID-19 vaccines are typically mild to moderate. Some of them may affect an individual’s ability to carry out their daily activities, but they should go away in a few days, according to the Centers for Disease Control and Prevention (CDC). There are instances when recipients do not experience side effects at all, while allergic reactions to the booster shots are very rare.

Just like the first two doses of the vaccines, the public health agency also warned that one should contact a doctor or a healthcare provider right away if the redness or tenderness of the site of injection gets worse after 24 hours of administration. Professional help is also needed if the symptoms do not go away or diminish in severity after a few days.

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