Does the Moderna vaccine require 2 doses?

Quick Answer

Yes, the Moderna COVID-19 vaccine requires 2 doses given 28 days apart to provide full protection against the SARS-CoV-2 virus that causes COVID-19. Both doses are necessary to develop high levels of neutralizing antibodies against the spike protein of the virus. The efficacy of the vaccine after just one dose is around 80-90%, while the efficacy after 2 doses is around 94-95%.

How many doses are required for the Moderna COVID-19 vaccine?

The Moderna COVID-19 vaccine requires 2 doses given 28 days apart to provide full protection against the SARS-CoV-2 virus. Both the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) recommend receiving 2 doses of the Moderna vaccine spaced 1 month (28 days) apart. The 2 dose series primes the immune system and provides optimal protection against COVID-19.

FDA guidelines

The U.S. FDA granted Emergency Use Authorization (EUA) for the Moderna COVID-19 vaccine requiring 2 doses given 28 days apart. The FDA EUA fact sheet states that the Moderna COVID-19 vaccine regimen is 2 doses (0.5 mL each) administered 1 month apart to individuals 18 years of age and older.

CDC recommendations

The U.S. CDC also recommends receiving 2 doses of the Moderna vaccine spaced 28 days apart. The CDC states that people must receive both doses of the vaccine to get the most protection the vaccine has to offer against the SARS-CoV-2 virus.

Efficacy after 1 dose vs. 2 doses

While the Moderna vaccine provides some protection after just 1 dose, the efficacy is significantly higher after the 2 dose series.

Efficacy after 1 dose

Studies found the efficacy of the Moderna vaccine against COVID-19 was around 80-90% after just one dose. However, experts say this level of efficacy is not enough for adequate protection, especially against new variants.

Efficacy after 2 doses

The efficacy of the Moderna vaccine rises to around 94-95% after the second dose. The high efficacy after the full 2-dose series provides robust protection against both the original SARS-CoV-2 virus and new emerging variants.

How the 2-dose series works

The first dose of the Moderna vaccine primes the immune system, while the second dose boosts the immune response. This prime-boost strategy provides strong, long-lasting protection.

Priming the immune system

The first dose introduces the body to the spike protein of the SARS-CoV-2 virus. This primes the immune system to recognize the virus and begin building antibodies against the spike protein. However, protection after one dose is still low.

Boosting the immune response

The second dose given 28 days later boosts the immune response. This allows the body to produce high levels of antibodies against the spike protein and generate immune memory. The boosted response provides robust, durable protection.

Duration of protection

While the duration of protection from the Moderna vaccine is still under investigation, studies so far indicate immunity lasts at least 6 months after the 2-dose series. Ongoing studies are monitoring antibody levels to determine the need for booster shots.

Protection up to 6 months

Clinical trial data showed the Moderna vaccine maintained an efficacy of over 90% for at least 6 months after the second dose. Real-world studies also found sustained antibody levels 6 months post vaccination.

Potential need for boosters

It is not yet known exactly how long protection will last. However, antibody levels do begin declining over time. Most experts predict booster shots will eventually be needed to maintain immunity, possibly within a year after getting vaccinated.

Strength of immune response

The immune response generated by the 2-dose Moderna series is robust and much stronger than the natural immunity from a COVID-19 infection.

Robust antibody levels

Studies found antibody levels against the SARS-CoV-2 virus spike protein were extremely high one month after the second Moderna dose. The potent immune response produces high concentrations of neutralizing antibodies.

Greater than natural immunity

The Moderna vaccine stimulates antibody levels that are up to 50 times higher than those developed after a natural COVID-19 infection. The vaccine provides a much stronger immune response compared to natural immunity.

Protection against variants

While the efficacy of the Moderna vaccine is slightly lower against variants like Delta and Omicron, studies show 2 doses still provide good protection, especially against severe disease.

Efficacy vs. Delta variant

Against the Delta variant, the efficacy of Moderna after 2 doses was around 95%. While slightly reduced, this indicates maintained strong protection.

Efficacy vs. Omicron variant

The efficacy of the Moderna vaccine was around 70% against Omicron infection after 2 doses. However, the vaccine still provided around 90% protection against hospitalization from Omicron.

Side effects

The Moderna vaccine can cause side effects after each dose, but these are typically mild to moderate and resolve within a few days. Side effects may be more pronounced after the second dose.

Common side effects

Common side effects after each Moderna dose include pain/swelling at injection site, fatigue, headache, muscle pain, joint pain, chills, nausea, fever. Side effects are more common after the second dose.

Rare side effects

In rare cases, the Moderna vaccine has been linked to severe allergic reactions (anaphylaxis) or heart inflammation (myocarditis, pericarditis), particularly in young men after the second dose. However, these reactions are very rare.

Reasons for 2-dose schedule

There are important scientific reasons supporting the 2-dose schedule for the Moderna COVID-19 vaccine.

Achieve high efficacy

The main reason for the 2-dose schedule is to achieve the high efficacy of around 95% demonstrated in clinical trials. The prime-boost regimen produces robust neutralizing antibodies.

Generate immune memory

The second dose helps generate strong immune memory. Immune memory provides long-lasting protection and rapid response to infection. Memory is critical for durable immunity.

Prepare for variants

Two doses help prepare the immune system to respond to SARS-CoV-2 variants that may evade antibodies from a single dose. The broad response from 2 doses gives better protection against new variants.

One dose vs. two doses

Getting only one dose of the Moderna vaccine provides insufficient protection, especially against variants of concern. Two doses are essential to achieve the intended efficacy.

Insufficient immune response

One dose only primes the immune system but does not generate robust neutralizing antibodies. The immune response from a single dose is minimal and not durable.

Weaker variant protection

Against variants like Delta and Omicron, protection from just one Moderna dose is significantly lower compared to two doses. Two doses are critical for protection versus variants.

Recommendation for full vaccination

Health authorities worldwide uniformly recommend receiving the full 2-dose series of the Moderna COVID-19 vaccine. Completing both doses provides the best protection against the SARS-CoV-2 virus and variants.


The U.S. FDA EUA specifies two doses of the Moderna vaccine spaced one month apart, stating this is the regimen proven to be safe and effective in clinical trials.

CDC guidance

The CDC advises completing the full Moderna vaccination schedule by receiving both required doses to get maximal protection. This provides the greatest individual and public health benefit.


In conclusion, the Moderna COVID-19 vaccine is designed and scientifically proven to require 2 doses administered 28 days apart to achieve its high efficacy of around 95%. Both doses work together to generate strong immune memory and high neutralizing antibody levels that provide optimal protection against the SARS-CoV-2 virus and circulating variants. All public health authorities strongly recommend receiving the full 2-dose series to get the greatest benefit from the Moderna vaccine.

Dose Efficacy Duration of Protection
1 dose 80-90% At least 6 weeks
2 doses 94-95% At least 6 months

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