Women and people age 80 years and older are more likely to report side effects after a third, or booster, dose of the Pfizer-BioNTech COVID-19 vaccine than other older adults, a study published Monday found.

However, side effects among adults age 60 years and older in the study were "generally mild" and "usually did not require medical care," the data, published Monday by JAMA Network Open, showed.

The percentage of booster-dose recipients who reported side effects was "similar or lower" than those seen following administration of the second vaccine dose in several previous studies, the researchers said.

"Individuals older than 60 receiving the third dose do not experience additional discomfort or adverse effects compared to previous doses," study co-author Dr. Shay Ben-Shachar told UPI in an email.

"Actually, they may even feel a slight better," said Ben-Shachar, director of precision medicine and genomics at Clalit Innovation, an Israel-based health research firm.

The findings are based on side effect reports from more than 82,000 Israelis age 60 years and older who received a third, booster dose of the Pfizer-BioNTech COVID-19 vaccine, Ben-Shachar and his colleagues said.

The two-dose Pfizer-BioNTech shot, which like the Moderna product uses mRNA technology, is the primary one available in Israel, the researchers said.

The Moderna and Pfizer-BioNTech vaccines, both of which require two initial doses, are the recommended inoculations against COVID-19 in the United States, according to the Centers for Disease Control and Prevention.

The agency recommends booster doses for people age 12 years and older and a fourth shot for those age 50 years and older or those with compromised immune systems due to cancer or other health problems.

Previous studies have reported "low-severity" side effects with booster doses of the Pfizer-BioNTech vaccine.

The company recently indicated it will apply for clearance to provide booster doses of the vaccine to children ages 5 to 11 years.

In this study, 30% of the participants reported at least one side effect following receipt of the third dose, with pain at the injection site, fatigue and malaise the most common, the data showed.

Among the participants, 39% of women reported at least one booster-dose side effect, compared with 23% of men, the researchers said.

Muscle aches, reported by 6% of participants, and headache, experienced by 5%, were also common, according to the researchers.

Just over 1% of the reported side effects among participants required medical attention, they said.

More than three-fourths of the participants said they did not experience side effects after the second dose of the vaccine, the data showed.

However, 68% indicated they "felt similar" after the third dose compared with the second, while 19% said they "felt better" following the booster, the researchers said.

Among participants age 80 years and older, 37% reported at least one side effect, compared with 33% of those ages 60 to 69 years and 25% of those ages 70 to 79 years, according to the researchers.

More than half of participants who reported side effects said their symptoms lasted three or more days, the data showed.

"We have tested only the third dose but it is unlikely that while adverse events were so similar in the first two doses and the third one that a different situation may characterize the fourth dose," Ben-Shachar said.

"We'd expect that the population will benefit from that dose without increased adverse events, as well," he said.

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