The study, published in the journal JAMA Network Open on Thursday, found that third doses did not result in an increase in serious side effects compared to previous doses, but led to an increase in low-severity side effects such as fatigue and nausea. .
“The results of this cohort study suggest that a third dose of the same type of vaccine following a primary BNT162b2 or mRNA-1273 series is associated with safe results,” the study said.
The COVID-19 vaccines produced by Pfizer-BioNTech and Moderna were originally designed as two-dose regimens, supported by extensive clinical trials. As studies showed signs of reduced vaccine immunity, health experts began to suggest booster vaccines, which were found to be safe and effective. However, there is still less data on these third doses than on the first and second doses, a knowledge gap that the researchers hoped to close in this new study.
The researchers had access to electronic medical records provided by 47,999 adults at the Mayo Clinic Enterprise, a nonprofit hospital system in the United States, who were all vaccinated with three doses of the same COVID-19 mRNA vaccine between December 2020 and October 17, 2021.
About 38,000 participants received the Pfizer-BioNtech vaccine for their three doses, while about 9,900 received the Moderna vaccine.
There were more than twice as many immunosuppressed people in the Moderna group as in the Pfizer group. No brand-specific adverse reactions were reported in the study.
The most common side effects after taking the third dose were fatigue, temporary swollen lymph nodes, nausea and headache, with these symptoms being reported by about two to five percent of participants.
Less than two percent of participants reported other common side effects such as joint pain, muscle aches, diarrhea and fever.
These numbers, although still small, represented a significant increase in how often the participants themselves reported these side effects after their first or second dose.
After the third dose, two patients had anaphylaxis, four patients developed tissue swelling around the heart called pericarditis, and one patient reported myocarditis, meaning that only 0.01 percent of participants reported one of these serious side effects.
“Reporting of serious adverse reactions was rare after the third dose and did not increase significantly compared with the reporting frequency after the second dose,” the study said.
The researchers also monitored participants’ emergency department visits within two days of receiving each dose of the vaccine and found that there was an increase in emergency visits after a third dose of the Pfizer vaccine compared to the second. Overall, 0.29 percent of people visited the emergency department after a third dose versus 0.2 percent after the second dose.
There was no difference in ER visits for different doses for those receiving Moderna.
The overall results show that the third dose is indeed safe, as it is not accompanied by an increase in serious side effects, the researchers said. They added that third doses had a better safety profile in this study than a single dose.
“People who just received it [one] The dose of a mRNA-based COVID-19 vaccine had higher increases in the incidence of adverse reactions [one]compared to the original value, than observed in [three]”dose dose”, the study stated.
The researchers noted that there were limitations to the study, such as the fact that mixed doses of mixed doses were not included and that those taking third doses were more likely to be older and immunosuppressed, resulting in a potentially reduced immune response to the vaccine. show fewer negative effects.
Further studies in third doses hope to further enhance the safety profile of vaccine brands in order to further reduce the incidence of rare side effects, the study said.