The Moderna COVID-19 Vaccine in Pregnancy

The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

Active ingredient

Nucleoside-modified mRNA encoding the viral spike (S) glycoprotein of SARS-CoV-2

Delivery vehicle

Ipid nanoparticles

Method of administration

Deltoid IM injection

Recommended schedule

2 injections 28 days (+/- 4 days) apart (CDC, as of Aug 12, 2021). The interval can be extended to 42 days, if necessary (WHO).

Dosage per shot

Adult: 0.5 mL (100 μg)


18 years and older (As of Aug 12, 2021)


Clinical trial data have demonstrated an efficacy 94.1% in preventing symptomatic, laboratory-confirmed infection with the SARS-CoV2 ancestral strain following two doses, administered with the 28-day interval protocol. Similar efficacy has been documented against the Alpha variant (B. and the Beta variant (501Y.V2). As of August 2021, studies from a handful of countries have suggested moderately decreasing immunity and decreasing antibody levels against the Delta variant (B.1.617.2) after several months in those receiving any of the approved COVID-19 vaccines. As of early August 2021, a pre-print paper post on medRxiv suggests that the immunity may be maintained better after the Moderna (mRNA-1273) vaccine than after the Pfizer/BioNTech (BNT162b2), but it should be emphasized that these are pre-print data; the study has yet to be peer-reviewed (as of August 12). Even several months beyond the second dose, efficacy remains extremely good against severe disease and death caused by the Delta variant.


Recommended “when the benefits of vaccination to the pregnant woman outweigh the potential risks” (WHO). Currently, the benefits of COVID-19 vaccination far outweigh potential risks both in pregnancy and lactation, other than in rare cases of people who previously have suffered allergic reactions to ingredients in the vaccine, such as polyethylene glycol. However, globally, there is an abundance of policies and philosophies surrounding to what degree potential vaccine recipients should be able to assess the risk vs benefits on their own. COVID- 19 testing of pregnant women prior is not necessary prior to vaccination, nor should women delay or terminate pregnancy or terminating pregnancy on account of COVID-19 vaccination (WHO). There is no plausible mechanism supporting notions that this vaccine might present a particular danger during pregnancy or lactation. Maternal vaccination against may possibly protect newborns and nursing infants

Relation to Pregnancy and Lactation

Against endemic variants of SARS-CoV2, including the delta variant, while pregnancy is a risk factor for the development of severe COVID-19 in unvaccinated women and for preterm birth.

Adverse effects

Injection site : pain, erythema, swelling at injection site

Systemic : fatigue, headache, myalgia, chills, fever, nausea.

There have been rare, anecdotal reports of myocarditis and pericarditis in adolescents and young adults (which may include women of reproductive age), but the benefits of the COVID-19 vaccination are considered to outweigh the risks in young age groups. As of August 12, 2021, on account of Delta variant, which affects younger people more than previous variants, the balance is shifting still more in favor of vaccination for young people.

Pregnancy and Lactation Positions by Country for the Moderna Vaccine (Spikevax)

FDA Fact Sheet for Recipients and Caregivers


Baden LR, El Sahly HM, Essink B et al. Efficacy and Safety of the mRNA-1273 SARS- CoV-2 Vaccine. N Engl J Med. 2021 Feb 4;384(5):403-416. doi: 10.1056/NEJMoa2035389. Epub 2020 Dec 30. PMID: 33378609

Centers for Disease Control and Prevention. Moderna COVID-19 Vaccine Information for Healthcare Professionals. Accessed August 12, 2021

World Health Organization Moderna: mRNA-1273 Tracker. Accessed August 12, 2021.

World Health Organization. Interim recommendations for use of the Moderna mRNA- 1273 vaccine against COVID-19. Accessed August 12, 2021

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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