With the administration of COVID-19 vaccines, concerns have arisen about the side effects that tend to come along with receiving the vaccine.

Scientists have identified patterns about the severity of side effects that are based on factors such as age, sex, and health. Previous studies do show support for this; for example, one study found that women tend to have stronger immune reactions to pathogens (Mauvais-Jarvis, Klein, and Levin 2020). Another preprint study, which is loosely related, investigated whether or not seropositive (meaning the individual already has the COVID-19 antibodies) individuals need a second vaccine dose, or if they were adequately protected against COVID-19 after the first vaccination (Krammer, Srivastava, and Simon 2021). The preprint article led to an interest in whether seropositivity is associated with severity of side effects of the vaccine. The most widely administered vaccines, and the ones that require two doses, are made by Pfizer and Moderna. The Pfizer and Moderna vaccines are mRNA vaccines, meaning that they inject mRNA from the COVID-19 virus. This mRNA contains the code to make spike proteins, or S proteins, that are located on all coronaviruses. After injection, the human cells will use this mRNA to create a harmless S protein that the immune system will then respond to. This allows the immune system to create antibodies before a “real” COVID-19 infection. This mechanism is what makes vaccines effective; they preemptively introduce the pathogen so that the body is ready to defend itself once the virus actually infects the host. Despite this rather consistent cellular response to vaccines, there have still been some observed discrepancies in the side effects. In this observational study, I set out to investigate whether or not sex, age, and previously having COVID-19 affect the severity of side effects after receiving the vaccine.

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