Understanding and Communicating Vaccine Efficacy and Effectiveness

Confusing messages about how well COVID-19 vaccines work pose a barrier to public understanding and broad vaccine uptake. When deciding whether to get vaccinated, members of the public may ask, “Should I take the currently available vaccine or wait for a ‘better’ one?” “Do the differences really matter?” “Is my community being treated fairly?” To answer these questions, public officials at all levels can use clear, consistent, and readily accessible communications to build a shared understanding of vaccine efficacy and promote uptake among vaccine-hesitant populations. 

This new guidance from the Societal Experts Action Network (SEAN) can help public officials prepare and evaluate their communications efforts around vaccination. For additional information on public engagement and communications strategies for building confidence in COVID-19 vaccines, view SEAN’s earlier guidance.

Vaccine Efficacy and Vaccine Effectiveness

To explain to a diverse public how well the COVID-19 vaccines work, public officials need to explain the concepts of vaccine efficacy and vaccine effectiveness.

  • Vaccine efficacy is a measure of how well a vaccine prevents a certain negative outcome (whether that is infection, severe symptoms, hospitalization, or death) in a clinical trial. For example, a vaccine with 95 percent efficacy means that in a population in which 100 in 10,000 unvaccinated people are hospitalized due to COVID-19 during a given period, only 5 in 10,000 vaccinated people, on average, would be hospitalized in the same period.
  • Unlike vaccine efficacy, vaccine effectiveness is measured in real-world settings with observational studies. Typically, a vaccine’s effectiveness is lower than its efficacy. A wide range of factors—including medications taken, general health status, and storage conditions of administered vaccines, among others—can alter a vaccine’s effect under real-world conditions and increase the variability in responses among those vaccinated.

Learn More

These rapid expert consultations were produced by SEAN (supported by the National Science Foundation and the Alfred P. Sloan Foundation) and the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats (supported by the Department of Health and Human Services and the Office of Science and Technology Policy).

Read the guidance online at https://www.nap.edu/resource/26154/interactive.

How can SEAN help?

Are you a policy maker? Do you have a question you need answered? SEAN will consider the most pressing questions and engage the nation’s experts to focus on your challenges. Contact us at SEAN@nas.edu or 202-334-3440.

SEAN is a network of experts in the social, behavioral, and economic sciences poised to assist decision makers at all levels as they respond to COVID-19. The network appreciates any and all feedback on its work. Please send comments to SEAN@nas.edu