Editors’ Note: This article was accepted on Dec. 28, 2020, and was accurate at that time. Because information about SARS-CoV-2 and COVID-19 is evolving rapidly, please verify these recommendations and information.

After witnessing more than 300,000 patients perish from COVID-19, including thousands of our health care colleagues, and despite record-setting hospitalizations in December, 2020 ended with a glimmer of hope: On Dec. 11, 2020, the Food and Drug Administration (FDA) granted emergency use authorization (EUA) for the Pfizer-BioNTech mRNA coronavirus vaccine, followed one week later by an EUA for Moderna’s version of the vaccine. At the time of this writing (Dec. 28), the Oxford-AstraZeneca adenovirus-based coronavirus vaccine had not yet received EUA from the FDA, though published data suggested efficacy ranging from 62 to 90 percent, with recent reports claiming even higher numbers.^1,2 When the pandemic began, very few experts believed that an effective vaccine would be available so soon, making vaccines the high point of an otherwise dismal year for science and public health.

In the United States, the first wave of individuals to receive the Pfizer and Moderna vaccines outside of clinical trials has mainly been composed of health care workers. The “vaccine selfie” quickly became the meme of the moment, with many emergency physicians posting pictures and videos of themselves getting their first dose on social media for all to see. Naturally, the media covered a few instances of systemic allergic reactions requiring epinephrine, but so far, among the nearly 2 million doses given here, the safety reports have been encouraging. Many people experienced pain at the injection site, and a sizeable number, perhaps 3 percent, experienced symptoms bothersome enough to temporarily inhibit usual activities of daily life and work. But all of that pales in comparison to the more than 3,000 Americans currently dying daily of COVID-19 among those who have not yet been vaccinated.

Three Big Questions Answered

Over the next few months, we can expect three common questions: 1) Should I get the vaccine when it is available to me? 2) Should I be vaccinated if I was already infected with the coronavirus and I recovered? 3) Which vaccine is best?

The answer to the first question is easy in most cases: yes. Compared to getting COVID-19, which has killed 1 in 1,000 Americans already, the side effects associated with these “reactogenic” vaccines are minor. The answer to the second question is that those with suspected or confirmed previous infections should be vaccinated, though only after symptoms have ceased. (Note: It is possible that immunity from the vaccines will be stronger and longer-lasting than that from natural infection, though research is ongoing.)

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

Moreover, SMFM states that for breastfeeding mothers, the biological plausibility of harm to the child is essentially nil.11 Even if the mRNA or lipid packaging of the vaccine made its way into breastmilk (unlikely), the child’s own digestive tract would metabolize it such that even if such substances were somehow dangerous (though they are not believed to be), the exposure risk actually approaches zero. Currently, only smallpox and yellow fever vaccines are contraindicated for breastfeeding mothers, as they are based on live-attenuated viruses.

For more information regarding COVID-19 vaccines, follow the CDC and Infectious Diseases Society of America.

References

1. Voysey M, Clemens SAC, Madhi SA, et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK [published online ahead of print Dec. 8, 2020]. Lancet. doi: 10.1016/S0140-6736(20)32661-1.
2. AFP. AstraZeneca: ‘Winning’ vaccine formula is 100% effective against severe COVID-19. The Times of Israel website. Available at: https://www.timesofisrael.com/astrazeneca-winning-vaccine-formula-is-100-effective-against-severe-covid-19. Accessed Dec. 28, 2020.
3. Moderna COVID-19 vaccine. CDC website. Available at: https://www.cdc.gov/vaccines/covid-19/info-by-product/moderna/index.html. Accessed Dec. 28, 2020.
4. FDA briefing document: Moderna COVID-19 vaccine. FDA website. Available at: https://www.fda.gov/media/144434/download. Accessed Dec. 28, 2020.
5. Pfizer-BioNTech COVID-19 vaccine. CDC website. Available at: https://www.cdc.gov/vaccines/covid-19/info-by-product/pfizer/index.html. Accessed Dec. 28, 2020.
6. Review of efficacy and safety of ​Pfizer-BioNTech COVID-19 vaccine ​emergency use authorization request. FDA website. Available at: https://www.fda.gov/media/144337/download. Accessed Dec. 28, 2020.
7. Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. CDC website. Available at: https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html. Accessed Dec. 28, 2020.
8. COVID-19 ACIP vaccine recommendations. CDC website. Available at: https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/covid-19.html. Accessed Dec. 28, 2020.
9. Vaccinating pregnant and lactating patients against COVID-19. American College of Obstetricians and Gynecologists website. Available at: https://www.acog.org/Clinical/Clinical%20Guidance/Practice%20Advisory/Articles/2020/12/Vaccinating%20Pregnant%20and%20Lactating%20Patients%20Against%20COVID%2019. Accessed Dec. 28, 2020.
10. Coronavirus (COVID-19). Society for Maternal-Fetal Medicine website. Available at: https://www.smfm.org/covid19. Accessed Dec. 28, 2020.
11. Considerations for COVID-19 vaccination in lactation. Academy of Breastfeeding Medicine website. Available at: https://abm.memberclicks.net/abm-statement-considerations-for-covid-19-vaccination-in-lactation. Accessed Dec. 28, 2020.

Dr. Niforatos is an emergency medicine resident at the Johns Hopkins School of Medicine in Baltimore and research editor of Brief19.com. Follow him on Twitter @ReverendofDoubt and follow Brief19 @Brief_19.