The COVID-19 vaccine made by Pfizer-BioNTech was granted approval for emergency use on December 11, 2020, for individuals ages 16 years and older. It was the first COVID-19 vaccine authorized for emergency use in the United States. It is an mRNA vaccine, similar to the Moderna vaccine.

The Pfizer vaccine requires two doses and works by providing your body with instructions on how to make the spike protein unique to this coronavirus. Your immune system processes this information and then builds an immune response, including antibodies.

To be fully effective, the Pfizer vaccine requires two doses, ideally 21 days apart. That being said, the vaccine has shown to have a high efficacy rate after a single dose, up to 85 percent, according to a 2021 study published in the Lancet.

Many transmissions occur after the first dose, within the first 10 days after the vaccination, before the body can produce enough antibodies.

Public Health England (PHE) conducted a study that reanalyzed a study previously published in the New England Journal of Medicine on the efficacy of the Pfizer vaccine.

The PHE reanalysis determined that this vaccine had an 89 percent efficacy rate for days 15 to 21 after dose one and before the second dose on day 21 as shown in Table 1. The range in this study was between 52 percent and 97 percent.

After the second dose, up to the first week afterward, protection from the first dose went up to 91 percent, with the range also going up from 74 percent to 97 percent.

Efficacy measures how well a vaccine works in a clinical trial, which is a controlled setting with a defined population.

Real-world effectiveness can be lower because of various reasons, but this is not a reflection on the vaccine. The vaccine was found to reduce transmissions, including those that were asymptomatic, by about 90 percent in a “real-world” setting.

Clinical trials only show what is going on with the virus at that specific time. By the time the vaccine is given to the general population, the prevalence of the virus might have changed, and new variants might be present. This is another reason why real-world effectiveness might be different from the clinical trial results. This is normal and is to be expected.

None of the existing vaccines can completely prevent transmission. This is why it is still important to wash your hands regularly, wear a mask, and practice social distancing.

No vaccine is 100 percent effective for everyone. This means there will still be COVID transmissions in vaccinated people. This is to be expected. Regarding the variants, the Pfizer vaccine has been found to significantly reduce the rate of transmission and serious illness.

A study in Qatar found that those who were vaccinated with the Pfizer vaccine were 75 percent less likely to develop COVID-19 caused by the variant first discovered in South Africa than unvaccinated individuals and were almost completely protected from severe disease from the infection.

Another study found that fully vaccinated individuals with the Pfizer vaccine were 90 percent less likely to develop COVID-19 from the variant first discovered in the United Kingdom. If they did, there were almost no severe cases. This is promising news for Pfizer’s efficacy against the variants.

There are three COVID-19 vaccines available in the United States that are authorized for emergency use:

  • Moderna
  • Pfizer
  • Johnson & Johnson

AstraZeneca has not yet been granted authorization in the United States.

All of the vaccines are effective and medical professionals do not recommend one over the other.

Laboratory results of efficacy for each vaccine include:

  • Pfizer: 95 percent efficacy in preventing an infection in people with no prior infections.
  • Moderna: 94.1 percent effective at preventing a symptomatic infection in people who have not previously contracted a coronavirus infection.
  • Johnson & Johnson: 72 percent overall efficacy and 86 percent efficacy against severe illness.
  • AstraZeneca: 76 percent effective at reducing the risk of symptomatic disease after both doses, and 100 percent effective against severe disease. The company has also claimed an 86 percent effectiveness rate of preventing a coronavirus infection in people over age 65 years.

Comparing the vaccines is difficult because each company may set up the terms of their clinical trials differently. This can include defining terms in different ways or how they measure things. The demographics of the trials can vary, and trials may be done at different times, which means the variants present at that time vary as well.

If you’ve been able to get an appointment to receive the vaccine, you may have a few other questions about what happens next. We’ve answered a few common questions.

Is it OK to take medication to relieve pain before or after the vaccine?

If you’re nervous about side effects from the vaccine, you might be considering taking medication to relieve potential pain before your shot.

Don’t do that just yet.

Research published in the Journal of Virology found that taking a nonsteroidal anti-inflammatory drug (NSAID) like ibuprofen, which is often recommended to help relieve pain, may impair antibody production and potentially weaken parts of the immune response to the vaccine.

Taking drugs that are used to relieve pain after receiving the vaccine may not be a problem. In the late-stage clinical trials of the Pfizer vaccine, the participants were not prevented from taking these medications.

If I don’t have side effects, does it mean the vaccine isn’t working?

If you do not have any side effects from the vaccine, it doesn’t mean your vaccine wasn’t effective. The side effects people experience are reflective of their individual immune systems, not of the efficacy of the vaccine.

Will I have to get a booster vaccine?

It is not known yet whether or when you will have to get a booster dose for the COVID-19 vaccine. Booster doses are an additional dose of the original vaccine.

This added dose to the vaccine regimen reminds the immune system about the infection and boosts antibody protection. The COVID-19 vaccine will likely be more like a flu vaccine, which changes every year. Because of new variants that might arise, you might have to get a new version of the vaccine that targets the mutations of the virus.

Is the vaccine less effective if you have a compromised immune system?

The vaccine may be less effective in some people with compromised immune systems. Even though it may produce a weaker immune response, any added protection against the coronavirus is beneficial.

Immunocompromised individuals are at higher risk for contracting the coronavirus and developing COVID-19, so the extra protection can help keep you healthy. If you are immunosuppressed, talk with your doctor before getting the vaccine.

The Centers for Disease Control and Prevention (CDC) does not recommend one vaccine over another. It is not advisable to wait for a certain brand. You should get the first COVID vaccine that is available to you.

The Pfizer COVID-19 vaccine is safe and effective, even against many variants of the virus. If you have any concerns or questions about it, talk with a medical professional.