An Overview of the Moderna COVID-19 Vaccine

Moderna's vaccine is the second to receive U.S. approval

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As cases of novel coronavirus (COVID-19) rise in a predicted winter surge, a number of vaccines are in the pipeline to help bring an end to the pandemic. One of these is Moderna’s vaccine, called mRNA-1273. Moderna’s vaccine is the second vaccine to receive emergency use authorization from the U.S. Food and Drug Administration (FDA).

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Moderna, an American biotechnology company based in Cambridge, Mass., began developing its vaccine in January 2020. The company worked with the National Institutes of Health (NIH) to finalize gene sequencing for the virus and began working on developing the vaccine soon after.

The first batch of the vaccine was developed in early February—just 25 days after the gene was sequenced. The first dose of the vaccine was given by March 2020 in a Phase 1 clinical trial, and those early trials showed promising results. By mid-year, Moderna received funding and fast-track regulatory allowances to help move development along.

While a vaccine initially wasn’t expected for 18 months or more, the new developments meant Moderna could deliver millions of doses much sooner. In August 2020, the U.S. government ordered 100 million doses of the vaccine—even though it hadn’t even been approved for use yet, and in November, results of the Phase 1 clinical trial were published.

In December, results from Phase 3 clinical trials were published and the U.S. ordered an additional 100 million doses.

When Was Moderna's Vaccine Officially Approved?

American health officials granted Moderna’s vaccine an emergency use authorization on Dec. 18 for adults 18 and older, making it the second vaccine to receive the designation from U.S. health officials in one week.

How It Works

The Moderna vaccine is an mRNA vaccine, similar to the one developed by Pfizer. The technology behind these vaccines has been around for about three decades and shown promise in preventing notoriously difficult-to-prevent diseases—even cancer. Unlike conventional vaccines that use inactivated or live viruses, mRNA vaccines are non-infectious and contain no parts of the virus they fight. This makes mRNA vaccines safer for certain populations.

An mRNA (messenger ribonucleic acid) vaccine is a single-stranded molecule that complements a strand of your DNA. These strands have a special coating that can protect mRNA from chemicals in the body that can break it down, and help it enter muscle cells.

Rather than exposing the body to a small amount of virus to create an immune response, mRNA causes the vaccine recipient to make the protein of interest. This includes:

  • Helping the cell make part of the spiked protein that makes COVID-19 so potent
  • Teaching immune cells to recognize and fight similar spiked proteins

According to the Centers for Disease Control and Prevention (CDC), mRNA vaccines teach our cells how to make a protein—or even just a piece of a protein. This triggers an immune response.

Moderna’s vaccine was initially tested in adults aged 18 to 55. The Phase 1 trial investigated three different doses—25-, 100-, and 250-micrograms—given twice, 28 days apart. By the Phase 3 trial, Moderna zeroed in on a two-dose formula of 100-micrograms each, given in two doses about four weeks apart.

How Was Moderna's Vaccine Tested?

Moderna's Phase 3 trial tested a two-dose vaccine (100-micrograms each, given 28 days apart) in adults ages 18 and older. The trial had more than 30,000 participants, including about 7,500 adults ages 65 and older and more than 5,000 adults ages 18 to 64 with risk factors for severe illness from COVID-19.

How Effective Is It?

Researchers that conducted the trials were able to test how effective the vaccine is in creating antibodies and neutralizing responses with tests that use bodily fluids like blood or urine to see whether antibodies to a particular virus can be found. These tests include:

  • ELISA (enzyme-linked immunosorbent assay) test
  • PsVNA (pseudotype lentivirus reporter single-round-of-infection neutralization assay)
  • PRNT (plaque-reduction neutralization test)

Antibody levels from these tests were compared to those found in people who had recovered from COVID-19 infections. The study investigated responses by other immune cells, like T-cells, too.

After the first round of vaccinations in the 100-microgram and 250-microgram formulas in the Phase 1 trial, antibody responses were similar to the median level of immunity in those who had recovered from and had natural immunity after a COVID-19 infection.

Other immunity tests, like the PsVNA , showed little response after the first dose. However, after the second doses, antibody and other immune responses were strong among the vaccination group—reaching levels that were close to those with the highest immune responses in those who had recovered from COVID-19.

Immune responses developed within about two weeks of the first dose, according to the trial report, but were much stronger after the second dose.

Exactly How Effective Is It?

Moderna’s vaccine has been shown in trials to be very effective—preventing COVID-19 in 94.1% of the people enrolled in the Phase 3 clinical trial. Additionally, the vaccine seems to have broad efficacy, with success rates consistent across various age, race, ethnicity, and gender groups.

The lifespan of these vaccines isn't clear yet, but the leaders of the trial say they will keep collecting blood samples from the study group to check for immunity throughout the first year after vaccination. In the past, viruses in the same virus families don't generate long-lived immune responses, the trial report notes. 

When Will It Be Available?

Moderna received emergency use authorization from the FDA for its vaccine on December 18.

Distribution may be a bit easier for Moderna than Pfizer since it’s vaccine can be stored at standard refrigerator temperatures for 30 days, or frozen at about -20 degrees Celsius for six months. The Pfizer vaccine has to be stored at much colder temperatures.

As far as cost goes, Moderna announced during an internal conference call in August that the vaccine could cost between $32 and $37 per dose, but final prices may change when the worst of the pandemic has passed.

According to the CDC, however, doses of the vaccines that have been purchased by the U.S. government will be available to citizens free of charge.

In addition to the 200 million doses already ordered by the U.S. government, it has the option to purchase 300 million more.

As of Jan. 26, Moderna had supplied 30.4 million doses to the U.S. and 10.1 of these doses had been administered, according to the company. Moderna also announced that it is on track to deliver 100 million doses to the U.S. by the end of March and the additional 100 million doses by the end of June.

The company has also reached agreements to supply the vaccine to several other countries, including:

  • European Union: 80 million initial doses with an option for another 80 million doses
  • Japan: 50 million doses
  • Canada: 40 million doses with an option for an additional 16 million
  • Switzerland: 7.5 million doses
  • United Kingdom: 7 million doses
  • Israel: 6 million doses

A number of other countries have also placed orders with the company, according to Moderna, but the number of doses ordered was not disclosed.

While the vaccine itself will be free if purchased by the government, there could be fees charged by vaccine providers who administer the vaccine. Reimbursement programs for these administrative costs should be available through both public and private insurance plans, as well as through the Health Resources and Services Administration's Provider Relief Fund for people with no public or private health insurance.

Who Can Get the Moderna Vaccine?

Now that vaccines are on the way, the question becomes who will get them and when? The CDC anticipated limited supplies in the initial phase of the vaccination program, and recommendations for who should receive the vaccine first were made by CDC's Advisory Committee on Immunization Practices (ACIP) in December 2020 based on earlier guidance from the National Academies of Sciences, Engineering, and Medicine.

In terms of the order, federal health officials decided that healthcare workers and people living in long-term care facilities should be the first to receive the first of the vaccines, which have been limited at first as manufacturing ramps up.

According to the CDC, there are more than 18 million healthcare providers in the U.S., and about 1.3 million Americans living in long-term care facilities. Each of these people would need to receive two doses of the top vaccine contenders so far, totaling nearly 40 million doses needed for the initial phase of vaccination. The CDC estimates it will take several months before the supply of vaccines catches up to the demand.

Guidance on who will receive the vaccine and when will be decided as supplies become available. The U.S. alone has a population of about 330 million—meaning nearly 700 million vaccine doses will be needed to vaccinate all of America as other vaccines follow a two-vaccine dose.

Although little information is available yet on the specifics of when everyone will receive the vaccination, and where they can get it, state and local health departments will be coordinating efforts to distribute doses of the vaccines as they become available. The vaccine should be available both in physician offices and retail locations like pharmacies that administer other vaccines.

The Moderna vaccine is given in two doses that are 28 days apart. The CDC recommends that the second dose be given as close as possible to the 28 days, yet grants a four-day grace period when it can be given slightly earlier and allows the second dose to be given within 42 days of the first dose in cases where the 28-day window isn't feasible.

When Will Children Be Able to Get the Vaccine?

Children will not receive the vaccine at first, as trials have only been conducted in adults. Moderna began recruiting participants for a clinical trial in 12- to 17-year-olds in December. Trials for younger children are still in the planning stages. Children and teens may be able to receive the vaccine later in 2021.

Side Effects and Adverse Events

People who took part in the study were asked to record any reactions to the vaccine, either to the area where the vaccine was injected or that they experienced overall. Pain at the site where the vaccine was injected and overall tiredness were the most common side effects in the Phase 3 trial.

Systemic effects are reactions that affect the entire body, and headache and fatigue topped that list and were most common in the vaccine group. Less than 20% of the people who were vaccinated report a fever after the second dose.

Local effects, on the other hand, affect only a small, limited area. The most common effect in this category was pain at the injection site.

The severity of reactions increased with the second dose of the vaccine. Few reactions were rated as severe with the first dose of the vaccine, but several were rated as severe after the second dose. The most common reactions reported by participants after the second dose of the vaccine were:

  • Pain at the injection site
  • Fatigue
  • Headache
  • Muscle aches
  • Chills
  • Joint pain

Nausea or vomiting, fever, red or swollen areas at the injection site, and swollen or enlarged lymph nodes were also reported. 

The percentage of serious adverse reactions was the same for the placebo and vaccine groups (.6%) and did not indicate any safety concerns. There was also no evidence of vaccine-associated enhanced respiratory disease in the trials. Previous vaccines for coronavirus in veterinary use and animal models have led to respiratory problems related to vaccination.

More observation will be done on the study groups as time goes on, and more studies are planned on special populations, like children.

Funding and Development

Moderna worked with the National Institutes of Health and the U.S. Department of Health and Human Services to develop its vaccine. The company received about $1.6 billion in federal funding through the Biomedical Advanced Research and Development Authority (BARDA)—a U.S. government program working to speed up the manufacture and distribution of vaccines to fight COVID-19. The U.S. government exercised its option for an additional 100 million doses from Moderna for around $1.68 billion.


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  1. Moderna. Time is of the essence to provide a vaccine against this pandemic virus.

  2. Jackson LA, et al. An mRNA vaccine against SARA-CoV-2—preliminary report. N Engl J Med 2020; 383:1920-1931. doi:10.1056/NEJMoa2022483

  3. Pardi, N., Hogan, M., Porter, F. et al. mRNA vaccines — a new era in vaccinologyNat Rev Drug Discov 17261–279 (2018). doi:10.1038/nrd.2017.243

  4. Centers for Disease Control and Prevention. Understanding mRNA COVID-19 vaccines. December 18, 2020.

  5. Baden LR, El Sahly HM, Essink B, et al. Efficacy and safety of the mrna-1273 sars-cov-2 vaccineN Engl J Med. Published online December 30, 2020:NEJMoa2035389. doi:10.1056/NEJMoa2035389

  6. Moderna. Moderna announces primary efficacy analysis in phase 3 COVE study for its COVID-19 vaccine candidate and filing today with U.S. FDA for emergency use authorization. Updated November 30, 2020.

  7. U.S. Food & Drug Administration. FDA takes additional action in fight against COVID-19 by issuing emergency use authorization for second COVID-19 vaccine. Updated December 18, 2020.

  8. Centers for Disease Control and Prevention. Frequently asked questions about the COVID-19 vaccine. Updated December 13, 2020.

  9. Moderna. U.S. government exercises 1st option for additional 100 million doses of Moderna’s COVID-19 vaccine candidate. Updated December 11, 2020.

  10. Moderna. Moderna provides U.S. COVID-19 vaccine supply update. Updated January 26, 2021.

  11. Dooling K, Marin M, Wallace M, et al. The Advisory Committee on Immunization Practices’ updated interim recommendation for allocation of COVID-19 vaccine — United States, December 2020MMWR Morb Mortal Wkly Rep 2021;69:1657-1660. doi:10.15585/mmwr.mm695152e2

  12. Centers for Disease Control and Prevention. Healthcare workers. Updated January 13, 2017.

  13. Centers for Disease Control and Prevention. 8 things to know about the U.S. COVID-19 vaccination program. Updated January 5, 2021.

  14. Centers for Disease Control and Prevention. Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. Updated January 21, 2021.

  15. U.S. Department of Health and Human Services. BARDA’s rapidly expanding COVID-19 medical countermeasure portfolio.

  16. Kansteiner F. With Pfizer shot spoken for, U.S. snaps up 100M more Moderna COVID-19 vaccine doses. Fierce Pharma. Updated December 14, 2020.