The answer to the third question is both easy and complicated. The most straightforward answer: “Get the one available to you first.” But for those who want to know more about the differences between the Pfizer-BioNTech and Moderna mRNA vaccines, let’s dive in.

Pfizer-BioNTech Versus Moderna

The differences between these two vaccines can be summarized as follows: differences in age indications, storage temperatures, dosing schedule, efficacy at preventing COVID-19 in persons ≥65 years of age, and frequency of systemic side effects and injection site reactions. (For more granular information, visit ACEPNow.com to view the table accompanying this article).

Both vaccines appear remarkably efficacious at preventing COVID-19 disease in general, and severe COVID-19 specifically.^3-6 The second dose of both the Pfizer-BioNTech and Moderna vaccines appears to induce a strong immune response resulting in a higher frequency of influenza-like illnesses than experienced after the first dose.^4,6 Health care workers should be aware of the potential to feel ill for a day or two after receiving either vaccine (especially after the second dose) and should be familiar with their hospital policy regarding post-vaccine symptoms that warrant work restrictions and testing for SARS-CoV-2.

Data are currently limited regarding vaccine safety and efficacy in demographics not included in the clinical trials, such as persons who are immunocompromised, have an autoimmune disorder, are pregnant or currently lactating, or are under the ages of either 16 or 18 years. Nevertheless, at the time of this writing, the Centers for Disease Control and Prevention (CDC) recommends the mRNA vaccine for persons who are immunocompromised, are living with HIV, have been diagnosed with an autoimmune disorder, have a history of Guillain-Barré syndrome stemming from a prior vaccination, or have a history of Bell’s palsy, provided that they have no contraindications to vaccination such as a history of anaphylaxis to any of the ingredients in the formulations.⁷

At the time of this writing, children younger than 16 or 18 years of age are not authorized to receive the Pfizer-BioNTech or Moderna vaccine, respectively.^4,6,7 We expect further recommendations from the American Academy of Pediatrics in the coming months.

Pregnancy and Lactation Concerns

Data are limited regarding safety of the mRNA vaccine among persons who are pregnant or lactating. The CDC and FDA state that pregnant persons in any demographic otherwise recommended to receive the vaccine, such as health care workers, may choose to be vaccinated.^7,8 Both the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) recommend routine vaccination with the mRNA COVID-19 vaccine in those who are pregnant or lactating if they are in one of the priority groups identified by the Advisory Committee on Immunization Practices (a committee within the CDC).^9,10 Notably, ACOG does not recommend routine pregnancy testing before receiving the COVID-19 vaccine.⁹