The Moderna COVID-19 vaccine was the second COVID-19 vaccine to be authorized for emergency use in the United States. It received authorization from the Food and Drug Administration (FDA) on December 18, 2020, about a week after Pfizer got approval.

It’s an mRNA vaccine, which means it uses the same technology and mode of action as the Pfizer vaccine.

It works by giving your body instructions on how to create the spike protein unique to this virus. Your body then creates antibodies that will recognize and attack those proteins if they come into contact with the virus.

Since its authorization, it has been shown to be safe and effective for adults over the age of 18.

The Moderna vaccine requires two doses to be fully effective. It was found that up to 14 days after the first dose, the effectiveness was 50.8 percent. After that, it was about 92.1 percent. After the second dose, it takes about 2 weeks for your body to build full immunity. After that time period, the vaccine is approximately 94.1 percent effective.

You should get your second dose as close to the 4-week mark as possible. If need be, it’s OK to get it up to 6 weeks after your first injection. We don’t currently know the impact of delaying the second dose even longer.

Efficacy typically measures how well a vaccine works in a clinical trial, which is a controlled setting. Real-world effectiveness may be lower because of various reasons. At full immunization, the effectiveness of the mRNA vaccines (Pfizer and Moderna) at reducing SARS-CoV-2 infections, including asymptomatic infections, in the real world is 90 percent.

The trials are just a snapshot of the virus in the world at that given time. When the vaccine goes out into the general population, the prevalence of the virus might have changed, as well as any variants that may be circulating. This is another reason that real-world effectiveness might vary from clinical trial results.

None of the existing vaccines can completely prevent transmission, which is why it is still important to wash your hands regularly and follow distancing and mask guidelines based on the situation, space, and vaccination status of those around you.

As the novel coronavirus mutates, different variants emerge. Some of these variants are more easily transmissible, which is why it’s important to know whether the COVID-19 vaccines are effective against any of these variants.

In January 2021, Moderna released a statement mentioning that the vaccine did show protective effects against all key emerging variants they tested. This included the variants first discovered in the United Kingdom and South Africa.

In May 2021, Moderna released an update on study results of a booster with previously vaccinated individuals. The booster dose was found to be effective in providing protection against two variants:

  • the variant first identified in South Africa
  • the variant first identified in Brazil

Given that new variants may emerge over time, the research on the vaccine’s efficacy will continue to evolve.

There are three COVID-19 vaccines available in the United States that are authorized for emergency use: Moderna, Pfizer, and Johnson & Johnson. AstraZeneca has not yet been approved in the United States. All of the vaccines are effective, so medical professionals do not recommend one over the other.

Laboratory results of efficacy for each vaccine were found to be:

  • Pfizer: 95 percent effective at preventing infection in those with no prior infections
  • Moderna: 94.1 percent effective at preventing symptomatic infection in those with no previous infection
  • Johnson & Johnson: 72 percent overall efficacy and 86 percent efficacy against severe disease
  • AstraZeneca: 76 percent effective at reducing the risk of symptomatic disease after two doses, and 100 percent effective against severe disease. The company has also claimed an 86 percent effectiveness rate of preventing COVID-19 in those over age 65.

Comparing the vaccines can be difficult because each company and their trials may define terms in different ways. The demographics of the trials can vary, and the time periods relative to the viral variants at the time can vary.

If you have decided to get vaccinated, you might have some other questions about how effective the vaccine is based on other circumstances. Here are some common questions.

Is it OK to take a pain reliever?

If you’re nervous about side effects from the vaccine, especially the second dose, you might be tempted to take some pain relievers ahead of time. This might not be the best course of action, as research published in the Journal of Virology has found that taking a nonsteroidal anti-inflammatory drug like ibuprofen may impair antibody production and reduce other parts of the immune response to the vaccine.

It is not known how this affects immunity outside the laboratory. Taking pain relievers after receiving the vaccine may not be a problem. In the late-stage clinical trials of the Moderna vaccine, the protocols did not prevent participants from taking these drugs if they felt they were necessary.

If I don’t have a reaction, does that mean the vaccine isn’t working?

If you don’t have any side effects from the vaccine, you may see the reactions other people have and wonder if your vaccine was effective. The good news is, yes, your vaccine was still effective and you are protected. The side effects people experience are just reflective of each individual’s unique immune system, not of the vaccine itself.

If I am immunocompromised, is the vaccine still effective?

For those who are immunosuppressed, talk with your doctor before getting any COVID-19 vaccine. While these vaccines are safe for the immunosuppressed, it’s always good to speak with your doctor about your individual situation.

The vaccine may be less effective in some people with compromised immune systems. That being said, even if the vaccine produces a weaker response, it may still be worth the added protection. People with weakened immune systems are at significant risk for COVID-19, so even some protection may be beneficial.

Will I need a booster?

There has also been a lot of talk about boosters for the COVID-19 vaccines. This is a bit of a misnomer. Boosters are typically an additional dose of the original vaccine to remind the immune system about the infection and boost antibody protection.

With the COVID-19 vaccine, because of emerging variants, it will likely be a new version of the vaccine to protect against the mutated forms of the virus.

You should get the first COVID-19 vaccine that is available to you. Waiting for a specific brand is not advised, and the Centers for Disease Control and Prevention (CDC) does not recommend one vaccine over another.

The Moderna COVID-19 vaccine is safe, effective, and comparable to the other COVID-19 vaccines on the market.

If you are immunocompromised or have any underlying health issues, talk with a medical professional about whether you should get the vaccine and any questions you might have about it.