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Moderna COVID-19 Vaccine

Last Updated: March 12, 2021

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Moderna’s COVID-19 vaccine is an mRNA vaccine that has been shown to be highly effective in preventing symptomatic COVID-19 disease. The vaccine, mRNA-1273, received emergency use authorization (EUA) from the U.S. Food and Drug Administration in December 2020 for use in individuals 18 years of age and older, making it the second COVID-19 vaccine authorized in the United States.

For information about U.S. COVID-19 vaccine availability and prioritization, refer to our page on vaccine distribution.

Key Literature

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine (Baden, December 2020).

Overall, in this phase 3 randomized, stratified, double-blind, placebo-controlled trial, mRNA-1273 was effective at preventing symptomatic COVID-19 disease and was safe at a median time to follow-up of 2 months.  

Study population: 

  • mRNA-1273 is an mRNA vaccine that is given in 2 doses, 29 days apart. 
  • mRNA-1273-P301 is a phase 3 ongoing randomized, stratified, double-blind, placebo-controlled trial. 
  • 30,420 participants over 18 years of age from 99 sites in the United States were randomized in a 1:1 manner to receive injections of either the mRNA-1273 (N=15,210) or a saline placebo (N=15,210) on day 1 and day 29. 
  • More than 96% of participants received both injections.
  • 66.3% of the study population was comprised of patients 18-64 years of age with risk for progression to severe COVID-19, and patients >=65 years of age.  
    • Patients were considered to have risk for severe disease if they had any of the following comorbidities: diabetes, chronic lung disease, severe obesity, significant cardiovascular disease, liver disease, or well-controlled HIV (persons with poorly controlled HIV were not included in the trial).
    • There were 179 patients living with HIV in the trial; data on this specific group has not yet been reported.  
  • The mean age of the participants was 51.4 years, 47.3% of the participants were female, 24.8% were >=65 years of age, and 16.7% were younger than 65 years of age and had predisposing medical conditions that put them at risk for severe COVID-19. 
  •  The majority of participants were white (79.2%)10.2% of participants were African American and 20.5% were Hispanic/Latinx. 
  • Patients had a negative SARS-CoV2-status at baseline (with a negative RT-PCR and negative serology against the SARS-CoV-2 nucleocapsid at day 1).  
    • 2.2% of study participants had serologic evidence of prior COVID-19. 
  • Participants were excluded if they were pregnant or breastfeeding, pediatric, immunocompromised, or had a known history of SARS-CoV-2. 
  • The interim primary efficacy analysis was based on the Per-Protocol Set, which consisted of 28,207 participants with negative baseline SARS-CoV-2 status and who received 2 doses of investigational product per schedule with no major protocol deviations.
    • The set included 14,134 patients in the vaccine group and 14,073 patients in the placebo group. 

Primary endpoints: 

  • EfficacyThe reduction of incidence of COVID-19 disease among participants without evidence of SARS-CoV-2 infection before the first dose of vaccine in the period after 14 days post-dose 2. 
  • The case definition of confirmed COVID-19 was: 
    • At least 2 of the following systemic symptoms: Fever (> 38C), chills, myalgia, headache, sore throat, new olfactory and taste disorder(s), or at least 1 of the following respiratory signs/symptoms: cough, shortness of breath or difficulty breathing, OR clinical or radiographic evidence of pneumonia; and 
    • Nasopharyngeal swab, nasal swab, or saliva sample (or respiratory sample, if hospitalized) positive for SARS-CoV-2 by RT-PCR. 
  • SafetyTo describe the safety of mRNA-1273 after 1 or 2 doses.  
    • Solicited events: participants recorded local reactions, systemic events, and antipyretic/pain medication usage from day 1 through day 7 after each dose. 
    • Unsolicited adverse events were collected from dose 1 to 28 days after the last dose.  
    • Medically attended adverse events and serious adverse events were also collected from dose 1 to the end of the study. 

Key Findings: 


  • Risk and demographics at baseline was reported in N=15,181 individuals receiving the vaccine and N=15,170 receiving placebo.  
  • At least one high-risk condition for severe COVID-19 was present in 27.1% of participants.  
  • There were no differences in demographics in the vaccines and placebo groups.  
  • As of November 25, 2020, the participants had a median follow-up duration of 64 days (range, 0-97) after the second dose, with 61% of participants having more than 56 days of follow-up. 
  • After day 1 and through November 25, 2020, a total of 269 COVID-19 cases were identified, with an incidence of 79.8 cases per 1000 person-years (95% confidence interval [CI], 70.5 to 89.9) among participants in the placebo group with no evidence of previous SARS-CoV-2 infection. Subgroup analyses of the primary efficacy endpoint showed similar efficacy across age groups, genders, racial and ethnic groups, and participants with medical comorbidities associated with high risk of severe COVID-19.  
  • For the primary analysis, 196 cases of COVID-19 were diagnosed: 11 cases in the vaccine group (3.3 per 1000 person-years; 95% CI, 1.7 to 6.0) and 185 cases in the placebo group (56.5 per 1000 person-years; 95% CI, 48.7 to 65.3), indicating 94.1% efficacy of the mRNA-1273 vaccine (95% CI, 89.3 to 96.8%; P<0.001) for the prevention of symptomatic SARS-CoV-2 infection as compared with placebo.  
  • Findings were similar across key secondary analyses including assessment starting 14 days after dose 1 (225 cases with placebo, vs. 11 with mRNA-1273, indicating a vaccine efficacy of 95.2% [95% CI, 91.2 to 97.4]), and assessment including participants who were SARS-CoV-2 seropositive at baseline in the per-protocol analysis (187 cases with placebo, vs. 12 with mRNA-1273; one volunteer assigned to receive mRNA-1273 was inadvertently given placebo], indicating a vaccine efficacy of 93.6% [95% CI, 88.6 to 96.5]).  
  • Between days 1 and 42, 7 cases of COVID-19 were identified in the mRNA-1273 group, as compared with 65 cases in the placebo group. 
  • A key secondary end point evaluated the efficacy of mRNA-1273 at preventing severe COVID-19.  
    • 30 participants in the trial had severe COVID-19; all 30 were in the placebo group (indicating vaccine efficacy of 100% [95% CI, could not be estimated to 1.0]), and one death among these participants was attributed to COVID-19. 
  • Among participants who were positive for SARS-CoV-2, by serologic or virologic testing, at baseline (337 in the placebo group and 343 in the mRNA-1273 group), 1 case of COVID-19 was diagnosed by RT-PCR testing in a placebo recipient and no cases were diagnosed in mRNA-1273 recipients 
  • Among participants who were negative for SARS-CoV-2 at baseline (by RT-PCR or antibody testing), in addition to symptomatic COVID-19 cases 39 (0.3%) in the placebo group and 15 (0.1%) in the mRNA-1273 group had nasopharyngeal swabs that were positive for SARS-CoV-2 by RT-PCR at the second dose visit (surveillance swab) but had no evidence of COVID-19 symptoms. 


  • Safety data at the time of the interim analysis was available for 30,347 participants, with a median follow-up of 2 months.
  • Solicited adverse events at the injection site occurred more frequently in the mRNA-1273 group than in the placebo group after both the first dose (84.2%, vs. 19.8%) and the second dose (88.6%, vs. 18.8%).
  • In the mRNA-1273 group, injection-site events were mainly grade 1 or 2 in severity and lasted a mean of 2.6 and 3.2 days after the first and second doses, respectively.
    • The most common injection-site event was pain after injection (86.0%).
    • Delayed injection-site reactions (those with onset on or after day 8) were noted in 244 participants (0.8%) after the first dose and in 68 participants (0.2%) after the second dose.
    • Reactions were characterized by erythema, induration, and tenderness, and they resolved over the following 4 to 5 days.
  • Solicited systemic adverse events occurred more often in the mRNA-1273 group than in the placebo group after both the first dose (54.9%, vs. 42.2%) and the second dose (79.4%, vs. 36.5%).
    • The severity of the solicited systemic events increased after the second dose in the mRNA-1273 group, with an increase in proportions of grade 2 events (from 16.5% after the first dose to 38.1% after the second dose) and grade 3 events (from 2.9% to 15.8%).
    • Solicited systemic adverse events in the mRNA-1273 group lasted a mean of 2.6 days and 3.1 days after the first and second doses, respectively.
    • Both solicited injection-site and systemic adverse events were more common among younger participants (18 to <65 years of age) than among older participants (≥65 years of age).
    • Solicited adverse events were less common in participants who were positive for SARS-CoV-2 infection at baseline than in those who were negative at baseline.
    • The frequency of unsolicited adverse events, unsolicited severe adverse events, and serious adverse events reported during the 28 days after injection was generally similar among participants in the two groups.
  • 3 deaths occurred in the placebo group (one from intraabdominal perforation, one from cardiopulmonary arrest, and one from severe systemic inflammatory syndrome in a participant with chronic lymphocytic leukemia and diffuse bullous rash) and 2 in the vaccine group (one from cardiopulmonary arrest and one by suicide).
  • The frequency of grade 3 adverse events in the placebo group (1.3%) was similar to that in the vaccine group (1.5%), as were the frequencies of medically attended adverse events (9.7% vs. 9.0%) and serious adverse events (0.6% in both groups).
  • Hypersensitivity reactions were reported in 1.5% and 1.1% of participants in the vaccine and placebo groups, respectively.
  • Bell’s palsy occurred in the vaccine group (3 participants [<0.1%]) and the placebo group (1 participant [<0.1%]) during the observation period of the trial (more than 28 days after injection).
  • No evidence of vaccine-associated enhanced respiratory disease was noted, and fewer cases of severe COVID-19 or any COVID-19 were observed among participants who received mRNA-1273 than among those who received placebo.
  • Adverse events that were deemed by the trial team to be related to the vaccine or placebo were reported among 4.5% of participants in the placebo group and 8.2% in the mRNA-1273 group.
    • The most common treatment-related adverse events (those reported in at least 1% of participants) in the placebo group and the mRNA-1273 group were fatigue (1.2% and 1.5%) and headache (0.9% and 1.4%).
  • In the overall population, the incidence of treatment-related severe adverse events was higher in the mRNA-1273 group (71 participants [0.5%]) than in the placebo group (28 participants [0.2%]).
    • The relative incidence of these adverse events according to vaccine group was not affected by age. 


  • The primary efficacy endpoint was clinical disease; asymptomatic infection was not assessed, although additional data utilizing a serologic endpoint is being collected. 
  • The trial did not include children, immunocompromised people, or pregnant women, but trials are being developed to assess mRNA-1273 in these groups.  
  • While there was a small group of people with evidence of prior COVID-19 infection at the time of analysis, the number of cases in this group was too small to draw any conclusions about the efficacy of the vaccine in individuals with prior infection; this may change as the trial continues. 
  • Serial RT-PCR testing was not performed, and so the efficacy of the vaccine in potentially preventing spread of SARS-CoV-2 could not be determined. 


Additional Literature

Safety and Immunogenicity of SARS-CoV-2 mRNA-1273 Vaccine in Older Adults (Anderson, December 2020): In this phase 1 open-label trial of mRNA-1273 in 40 older adults, who were stratified according to age (56 to 70 years or ≥71 years), participants were assigned sequentially to receive two doses of either 25 μg or 100 μg of vaccine administered 28 days apart. Solicited adverse events were predominantly mild or moderate in severity and most frequently included fatigue, chills, headache, myalgia, and pain at the injection site. Such adverse events were dose-dependent and were more common after the second immunization. By day 57, among the participants who received the 25-μg dose, the anti–S-2P geometric mean titer (GMT) was 323,945 among those between the ages of 56-70 years and 1,128,391 among those who were >=71 years of age; among the participants who received the 100-μg dose, the GMT in the two age subgroups was 1,183,066 and 3,638,522, respectively. Binding- and neutralizing-antibody responses appeared to be similar to those previously reported among vaccine recipients between the ages of 18-55 years.

Durability of Responses after SARS-CoV-2 mRNA-1273 Vaccination (Widge, December 2020): In this phase 1 open-label trial of mRNA-1273 in 34 healthy adults who received two injections of the vaccine 28 days apart , at a 119 day time point, geometric mean titers were: 235,228 (95% CI 177,236 to 312,195) in participants 18 to 55 years of age; 151,761 (95% CI, 88,571 to 260,033) in those 56 to 70 years of age; and 157,946 (95% CI, 94,345 to 264,420) in those 71 years of age or older. Serum neutralizing antibodies continued to be detected in all the participants at day 119. On a pseudovirus neutralization assay, the 50% inhibitory dilution geometric mean titer was 182 (95% CI, 112 to 296) in participants who were 18 to 55 years of age, 167 (95% CI, 88 to 318) in those 56 to 70 years of age, and 109 (95% CI, 68 to 175) in those 71 years of age or older.

An mRNA Vaccine against SARS-CoV-2 — Preliminary Report (Jackson, November 2020): In this phase 1 dose-escalation, open-label trial of mRNA-1273 in 45 healthy adults who received 2 doses of the vaccine 28 days apart, after 1 dose of the vaccine antibody responses were higher with higher dose (day 29 enzyme-linked immunosorbent assay anti–S-2P antibody geometric mean titer [GMT], 40,227 in the 25-μg group, 109,209 in the 100-μg group, and 213,526 in the 250-μg group). After the second vaccination, the titers increased (day 57 GMT, 299,751, 782,719, and 1,192,154, respectively). After the second vaccination, serum-neutralizing activity was detected in all participants. Systemic adverse events were more common after the second vaccination, particularly with the highest dose, and three participants (21%) in the 250-μg dose group reported one or more severe adverse events.

Dosing & Administration

The Moderna COVID-19 vaccination series consists of 2 intramuscular doses, 0.5 mL each, given 4 weeks apart. 

Second doses administered within a grace period of ≤4 days from the recommended date for the second dose are considered valid; however, doses administered earlier do not need to be repeated. The second dose should be administered as close to the recommended interval as possible. However, there is no maximum interval between the first and second dose for either vaccine. 

The Moderna COVID-19 vaccine is not interchangeable with other COVID-19 vaccines to complete the vaccination series. The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the Moderna COVID-19 vaccine. However, if two doses of different mRNA COVID-19 vaccine products are inadvertently administered, no additional doses of either product are recommended at this time.

Overall vaccine efficacy after one dose has not been studied. While there were patients in phase 3 trialwho received one dose and vaccine efficacy was reported in these patients, the overall number of such patients was small and they were only followed for a short time period. The duration and degree of their immune responses to the single dose of the vaccine is not known; until such data is available and the efficacy of one dose has been studied, FDA recommends that all COVID-19 vaccine recipients receive two doses of vaccine. 

Dose Preparation

  • The Moderna COVID-19 Vaccine multiple-dose vial contains a frozen suspension that does not contain a preservative and must be thawed prior to administration.
  • Remove the required number of vial(s) from storage and thaw each vial before use.
  • Thaw in refrigerated conditions between 2° to 8°C (36° to 46°F) for 2 hours and 30 minutes. After thawing, let vial stand at room temperature for 15 minutes before administering.
  • Alternatively, thaw at room temperature between 15° to 25°C (59° to 77°F) for 1 hour.
  • After thawing, do not refreeze.


  • Visually inspect each dose of the Moderna COVID-19 Vaccine in the dosing syringe prior to administration. The white to off-white suspension may contain white or translucent product-related particulates.
  • During the visual inspection:
    • Verify the final dosing volume of 0.5 mL.
    • Confirm there are no other particulates and that no discoloration is observed.
    • Do not administer if vaccine is discolored or contains other particulate matter.

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According to FDA guidance, individuals should not get the Moderna COVID-19 vaccine if they have:

  • A known history of a severe allergic reaction (e.g., anaphylaxis) to any component of the Moderna COVID-19 Vaccine:
    • A total lipid content of 1.93 mg (SM-102, polyethylene glycol [PEG] 2000 dimyristoyl glycerol [DMG], cholesterol, and 1,2-distearoyl-sn-glycero-3-phosphocholine [DSPC]);
    • 31 mg tromethamine;
    • 18 mg tromethamine hydrochloride;
    • 043 mg acetic acid;
    • 12 mg sodium acetate; and
    • 5 mg sucrose.
  • Of note, an immediate allergic reaction to a vaccine or medication is defined as any hypersensitivity-related signs or symptoms such as urticaria, angioedema, respiratory distress (e.g., wheezing, stridor), or anaphylaxis that occur within four hours following administration. 
  • CDC considers a history of the following to be a contraindication to vaccination with the Moderna COVID-19 vaccine: 
    • Severe allergic reaction (e.g., anaphylaxis) after a previous dose of an mRNA COVID-19 vaccine or any of its components 
    • Immediate allergic reaction of any severity to a previous dose of an mRNA COVID-19 vaccine or any of its components (including polyethylene glycol [PEG])*. 
    • Immediate allergic reaction of any severity to polysorbate (due to potential cross-reactive hypersensitivity with the vaccine ingredient PEG)*.
      • * These persons should not receive mRNA COVID-19 vaccination at this time unless they have been evaluated by an allergist-immunologist and it is determined that the person can safely receive the vaccine (e.g., under observation, in a setting with advanced medical care available). 
  • People with a history of anaphylaxis to any other vaccine or injectable therapy can still receive the Moderna COVID-19 vaccine, but should be counseled about the unknown risks of developing a severe allergic reaction, according to a December 2020 CDC presentation.
  • The following groups do not have a contraindication:
    • People who have a history of food, pet, insect, venom, environmental, latex, or other allergies not related to injectable therapies;
    • People with an allergy to an oral medication;
    • People with a non-serious allergy to other vaccines or injectables;
    • People with a family history of anaphylaxis; and
    • People any other history of anaphylaxis unrelated to a vaccine or injectable.
  • The vial stoppers of these mRNA vaccines are not made with natural rubber latex, and there is no contraindication or precaution to vaccination for persons with a latex allergy. In addition, as the mRNA COVID-19 vaccines do not contain eggs or gelatin, persons with allergies to these substances do not have a contraindication or precaution to vaccination.
  • People with no history of anaphylaxis should be monitored for 15 minutes after vaccination; people with a history of anaphylaxis should be monitored for 30 minutes.

CDC has provided considerations after administration of mRNA vaccines in health care personnel with systemic signs and symptoms following COVID-19 vaccination.

Post-Market Safety Monitoring

The Moderna COVID-19 Vaccine EUA Letter of Authorization includes specific instructions on continuous safety monitoring (see “Conditions of Authorization” on pages 5-9) in accordance with its requirement that all EUA sponsors “plan for active follow-up for safety, including deaths, hospitalizations, and other serious or clinically significant adverse events, among individuals who receive the vaccine under an EUA, to inform ongoing benefit-risk determinations to support continuation of the EUA.”

The federal government uses multiple vaccine safety monitoring systems to monitor COVID-19 vaccines in the post-authorization/approval period, including the Vaccine Adverse Event Reporting System, the Vaccine Safety Datalink, the Biologics Effectiveness and Safety Initiative, and Medicare claims data.

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Special Patient Populations/Settings

Previous SARS-CoV-2 Infection
At study enrollment in the phase 3 clinical trial, 2.2% of participants had serologic evidence of prior infection. Among this population, the attack rate of infection was low over the course of the study (no cases of symptomatic COVID-19 in 341 participants with serologic evidence of prior COVID-19 in the vaccinated group; 1 in 334 participants in the placebo group), according to a briefing document presented to the FDA. The number of events is too small to draw conclusions. The trial did collect serum and notes it will be reporting on the efficacy of the vaccine in people who became seropositive over the course of the study.

Vaccination should be offered to persons regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection. Viral testing to assess for acute SARS-CoV-2 infection or serologic testing to assess for prior infection solely for the purposes of vaccine decision-making is not recommended. 

Vaccination of persons with known current SARS-CoV-2 infection should be deferred until the person has recovered from the acute illness (if the person had symptoms) and criteria have been met for them to discontinue isolation. This recommendation applies to persons who develop SARS-CoV-2 infection before receiving any vaccine doses as well as those who develop SARS-CoV-2 infection after the first dose but before receipt of the second dose. 

As current evidence suggests that reinfection is uncommon in the 90 days after initial infection, the CDC states that individuals with documented acute SARS-CoV-2 infection in the preceding 90 days may delay vaccination until near the end of this period, if desired.

Passive Antibody Therapy Recipients
Currently, there are no data on the safety and efficacy of mRNA COVID-19 vaccines in persons who received monoclonal antibodies or convalescent plasma as part of COVID-19 treatment. Based on the estimated half-life of such therapies as well as evidence suggesting that reinfection is uncommon in the 90 days after initial infection, vaccination should be deferred for at least 90 days, as a precautionary measure until additional information becomes available, to avoid interference of the antibody treatment with vaccine-induced immune responses. 

For persons receiving antibody therapies not specific to COVID-19 treatment (e.g., intravenous immunoglobulin, RhoGAM), administration of mRNA COVID-19 vaccines either simultaneously with or at any interval before or after receipt of an antibody-containing product is unlikely to substantially impair development of a protective antibody response. Thus, there is no recommended minimum interval between other antibody therapies (i.e., those that are not specific to COVID-19 treatment) and mRNA COVID-19 vaccination. 

People Living with HIV/Immunocompromised
179 individuals with stable HIV disease were included in the phase 3 trial of the vaccine, but the safety data on this group has not yet been separately reported. People with significant immunocompromise were not included in the trial. As such, there is currently no data on vaccine efficacy or safety in these groups.

Persons with HIV infection or other immunocompromising conditions, or who take immunosuppressive medications or therapies might be at increased risk for severe COVID-19. Data are not currently available to establish vaccine safety and efficacy in these groups. Persons with stable HIV infection were included in mRNA COVID-19 vaccine clinical trials, though data remain limited. Immunocompromised individuals may receive COVID-19 vaccination if they have no contraindications to vaccination. However, they should be counseled about the unknown vaccine safety profile and effectiveness in immunocompromised populations, as well as the potential for reduced immune responses and the need to continue to follow all current guidance to protect themselves against COVID-19. Antibody testing is not recommended to assess for immunity to COVID-19 following mRNA COVID-19 vaccination. 

At this time, re-vaccination is not recommended after immune competence is regained in persons who received mRNA COVID-19 vaccines during chemotherapy or treatment with other immunosuppressive drugs. Recommendations on re-vaccination or additional doses of mRNA COVID-19 vaccines may be updated as additional information is available.

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All pregnancies have a risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically. recognized pregnancies is 2% to 4% and 15% to 20%, respectively. Pregnant people and children were excluded from Moderna’s COVID-19 clinical trial - additional evaluation of the vaccine in these groups is planned. 

Study participants of childbearing potential were screened for pregnancy prior to each vaccination, with a positive test resulting in exclusion or discontinuation from study vaccination. The study is collecting outcomes for all reported pregnancies that occur after vaccination, or before vaccination and not detected by pre-vaccination screening tests. Thirteen pregnancies were reported through December 2, 2020 (6 vaccine, 7 placebo). Study vaccination occurred prior to the last menstrual period (LMP) in 5 participants (2 vaccine, 3 placebo), within 30 days after LMP in 5 participants (2 vaccine, 3 placebo), >30 days after LMP in 2 participants (1 vaccine, 1 placebo), and date of LMP not known in 1 participant (1 vaccine, 0 placebo). Unsolicited AEs related to pregnancy include a case of spontaneous abortion and a case of elective abortion, both in the placebo group. One participant in the placebo group is lost to follow-up. Pregnancy outcomes are otherwise unknown at this time.

A combined developmental and perinatal/postnatal reproductive toxicity study of the Moderna COVID-19 vaccine in rats was submitted to FDA on December 4, 2020. FDA review of this study concluded that a dose of 100 μg given prior to mating and during gestation periods did not have any adverse effects on female reproduction, fetal/embryonal development, or postnatal developmental except for skeletal variations which are common and typically resolve postnatally without intervention.

The EUA does not exclude pregnant people; providers who wish to offer the Moderna COVID-19 vaccine to pregnant women may do so. Based on current knowledge, experts believe that mRNA vaccines are unlikely to pose a risk to the pregnant person or the fetus because mRNA vaccines are not live vaccines. The mRNA in the vaccine is degraded quickly by normal cellular processes and does not enter the nucleus of the cell. However, the potential risks of mRNA vaccines to the pregnant person and the fetus are unknown because these vaccines have not been studied in pregnant people. 

If pregnant people are part of a group that is recommended to receive a COVID-19 vaccine (e.g., healthcare personnel), they may choose to be vaccinated. A conversation between the patient and their clinical team may assist with decisions regarding the use of a mRNA COVID-19 vaccine, though a conversation with a healthcare provider is not required prior to vaccination. When making a decision, pregnant people and their healthcare providers should consider the level of COVID-19 community transmission, the patient’s personal risk of contracting COVID-19, the risks of COVID-19 to the patient and potential risks to the fetus, the efficacy of the vaccine, the side effects of the vaccine, and the lack of data about the vaccine during pregnancy. 

Side effects can occur with COVID-19 vaccine use in pregnant people, similar to those expected among non-pregnant people. Pregnant people who experience fever following vaccination may be counseled to take acetaminophen as fever has been associated with adverse pregnancy outcomes. Acetaminophen may be offered as an option for pregnant people experiencing other post-vaccination symptoms as well. 

The American College of Obstetricians and Gynecologists (ACOG) recommends that COVID-19 vaccines should not be withheld from pregnant individuals who meet ACIP criteria for vaccination. The Society of Maternal Fetal Medicine (SMFM) strongly recommends that pregnant and lactating people have access to COVID-19 vaccines and that they engage in a discussion with their health care providers about potential risks and unknown risks regarding receiving the vaccine. 

There are no data on the safety of Moderna’s COVID-19 vaccine in lactating people or the effects of mRNA COVID-19 vaccines on the breastfed infant or milk production/excretion. mRNA vaccines are not thought to be a risk to the breastfeeding infant. A lactating person who is part of a group recommended to receive a COVID-19 vaccine (e.g., healthcare personnel) may choose to be vaccinated.

According to the December 2020 CDC presentation noted above, mRNA vaccines are not considered live virus vaccines and are not thought to be a risk to a breastfeeding infant. If a lactating person is part of a group (e.g., healthcare personnel) who is recommended for COVID-19 vaccination, they may choose to be vaccinated.

ACOG recommends COVID-19 vaccines be offered to lactating individuals similarly to non-lactating individuals - when they meet criteria for receipt of the vaccine based on prioritization groups outlined by the ACIP. While lactating individuals were not included in most clinical trials, ACOG recommends that COVID-19 vaccines not be withheld from lactating individuals who otherwise meet criteria for vaccination.

Pediatric Use
Safety and effectiveness have not been assessed in people less than 18 years of age. Emergency Use Authorization of Moderna COVID-19 Vaccine does not include use in individuals younger than 18 years of age. However, Moderna has started trials for 12- to 17-year-olds.

Geriatric Use
Clinical studies of Moderna COVID-19 Vaccine included participants 65 years of age and older receiving vaccine or placebo, and their data contribute to the overall assessment of safety and efficacy. See Key Literature above.

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