Increasing vaccine availability in the U.S. and additional data on the safety and efficacy of booster shots has granted many Americans access to a third dose of the Pfizer and Moderna Covid-19 vaccines. Studies have shown that shots after the first dose improve immunity to the virus – one study found that the second dose increased the presence of a type of immune cell by up to 100-fold when compared to the first dose alone.1 Yet this benefit does not come without consequences. Many patients experience adverse side effects as a result of the immune system activation instigated by the Covid booster shot.
Side effects from the Covid-19 booster shot are common. A study of 12,591 patients who received their third mRNA Covid booster shot reported that 79.4 percent experienced local side effects and 74.1 percent experienced systemic reactions.2 While these numbers are comparable to the frequency of adverse symptoms for the second booster dose, the authors of the study noted slightly increased frequency of local symptoms and decreased frequency of systemic symptoms in patients who received the third dose. Commonly experienced local symptoms included pain/swelling near the site of injection, whereas systemic symptoms included fever, headache, fatigue/myalgia/arthralgia, nausea, vomiting, and chills. These are all considered to be mild symptoms and subside for most patients within several days following the injection.
More severe side effects from the Covid-19 booster shot have been reported, but at extremely low rates. Individuals who are most at risk for severe side effects are those with allergies to any of the compounds which make up the vaccine. For these individuals, receiving any dose of the vaccine is contraindicated, and other methods of infection prevention – including mask wearing, avoiding large social gatherings, and maintaining six feet of distance from other individuals – are strongly recommended. Instances of severe side effects should be reported directly to the CDC via the Vaccine Adverse Event Reporting System (VAERS).3 However, the vast majority of individuals may receive the vaccine safely.
Despite the commonality of adverse side effects from the mRNA Covid-19 booster shots, severe side effects have been shown to be extremely uncommon. The vast majority of side effects are temporary and do not pose serious hazards to vaccine recipients. Moreover, studies have shown that up to 97 percent of individuals hospitalized from Covid-19 are unvaccinated. Four-hundred and thirty-one unvaccinated individuals are hospitalized per 100,000, compared to 26 per 100,000 for individuals who are vaccinated. In other words, unvaccinated individuals are hospitalized at roughly 17 times the rate of those who have been vaccinated.
In sum, while one might expect to experience side effects from the booster dose of the Covid-19 vaccine, these symptoms are not cause for alarm and certainly should not deter one from receiving the vaccine. For more answers concerning potential vaccine side effects, efficacy, and other pertinent questions, the Centers for Disease Control and Prevention maintains a website (link here).
References
1 Arunachalam, P. S., Scott, M., Hagan, T., et al. (2021). Systems vaccinology of the BNT162b2 mRNA vaccine in humans. Nature, 10.1038/s41586-021-03791-x. Advance online publication. https://doi.org/10.1038/s41586-021-03791-x
2 Pfizer-BioNTech COVID-19 Vaccine Reactions & Adverse Events. (2021, October 12). Retrieved from https://www.cdc.gov/vaccines/covid-19/info-by-product/pfizer/reactogenicity.html
3 Understanding Adverse Events and Side Effects. (2021, March 30). Retrieved from https://www.cdc.gov/vaccinesafety/ensuringsafety/sideeffects/index.html