How effective are the COVID-19 vaccines — and what does that mean?

A doctor's hand with a syringe of covid-19 coronavirus vaccine.

Many people want to know how effective a vaccine is before getting one. In fact, nearly 30% of people we polled on BlueCross BlueShield of Tennessee social channels wanted to know more about COVID-19 vaccine effectiveness. But the word “effective” can mean different things, depending on what the goal is.

Overall vaccine effectiveness is how well a vaccine works to prevent disease for the general population.

So what does that mean specifically for COVID-19 vaccines? Here’s what you need to know.

What the clinical trials showed

Vaccine effectiveness begins by looking at its efficacy (how well it works). Experts measure how much a vaccine lowers the risk of an outcome (such as getting a disease). It’s tracked among tens of thousands of volunteers, under controlled circumstances.

The most common measure experts look for during trials is how well a vaccine prevents disease for people vaccinated, compared to those who received a placebo. So, the efficacy percentage reported by each manufacturer is the difference in that reduced risk among the two groups.

Think of it this way:

  • 0% = vaccine didn’t eliminate any risk
  • 50% = vaccine cuts the risk by half
  • 100% = vaccine eliminated the risk entirely

The World Health Organization, the FDA and other medical experts wanted COVID-19 vaccines to be at least 50% effective before recommending them for public use. So far, each authorized COVID-19 vaccine has far exceeded 50% efficacy in preventing infection.

Here are the results of each trial based on its objectives:

  • Pfizer-BioNTech: 95% effective against positive COVID-19 test results or symptomatic infection
  • Moderna: 94.1% effective against positive COVID-19 test results or symptomatic infection
  • Johnson & Johnson / Janssen: 72% effective against COVID-19-related moderate to severe illness and 85% against severe cases

Some trials have also taken a closer look at outcomes at specific trial sites around the world. Others have also looked at how well these vaccines have worked to reduce severe COVID-19 cases (keeping people out of the hospital or dying from the disease). These other outcomes were also above the threshold.

Dr. Andrea Willis explains what you need to know about the clinical trials in this Q&A.

What we’re learning in the “real world”

While efficacy is a strong indicator for how a vaccine will perform in the “real world,” it’s not completely accurate to suggest one vaccine is better than another based on the different outcomes observed during clinical trials.

A vaccine’s overall effectiveness casts a wider net beyond that.

For example, the latest COVID-19 vaccines were effective during trials, but experts are already seeing them work for the general population by:

  1. Ensuring those infected don’t experience severe illness,
  2. Decreasing the likelihood of transmission, and
  3. Reducing the risk for long-term effects and complications from natural exposure to COVID-19.

Once a vaccine reaches the public, we begin to see how effective it is in other ways besides simply preventing disease for those vaccinated. In fact:

3 things you should know about your own immunity and COVID-19 vaccines

To understand how vaccines work and what to expect when you get one, we first need to know how immunity works. Our immune system is sophisticated, but if this system stops running smoothly because it’s weak or doesn’t have enough time to respond adequately, we can get severely ill or die, as we’ve seen with COVID-19. This is when vaccines can help.

Here are 3 things to keep in mind when it comes to your own immunity and vaccines:

  1. Natural infection by many viruses can be serious and often deadly, but vaccines imitate infection so our immune system can learn how to better fight these germs.
  2. Each type of vaccine is specific to what it’s helping us build immunity against, and our immune systems need some time to create this protection after getting vaccinated.
  3. Variables such as medications you take, underlying health conditions, age and other factors could influence your specific level of immunity.

No one is exempt when it comes to dealing with the burden of infectious diseases like COVID-19. COVID-19 can continue to spread if not enough people get vaccinated which means everyone should get one if they can.

Need more advice?

First, get to know exactly how vaccines work and what to expect when you get one. If you have questions or concerns about vaccines based on your health status, speak to a provider who knows your medical history. Your friends and family may have good intentions, but they may not know your body like you and your doctor, so it’s important to speak to a provider who knows you well.

If you do decide to go online to learn more about vaccines, do seek reputable sources like the CDCFDA or World Health Organization (WHO). You can also visit BCBSTupdates.com to get the latest facts on and support for COVID-19 and vaccines, along with information on how BlueCross BlueShield of Tennessee is supporting its members and communities through the COVID-19 pandemic.

More COVID-19 vaccine stories from WellTuned

Suzanne Corrington, M.D.

Suzanne Corrington, M.D.

Dr. Corrington serves as medical director of care management services for BlueCross BlueShield of Tennessee where she directs teams and programs related to medical management and quality care initiatives. Before joining BlueCross in 2016, Dr. Corrington worked in emergency medicine, internal medicine for a private practice, and in clinic and hospital services.

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Filed under: Health Topics, Mind & Body

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Suzanne Corrington, M.D.

Dr. Corrington serves as medical director of care management services for BlueCross BlueShield of Tennessee where she directs teams and programs related to medical management and quality care initiatives. Before joining BlueCross in 2016, Dr. Corrington worked in emergency medicine, internal medicine for a private practice, and in clinic and hospital services.