How effective are the COVID-19 vaccines?

Assessing COVID-19 vaccine effectiveness under real-world conditions


With millions of cases of infections and hundreds of thousands of deaths in the U.S. alone, the public health burden of COVID-19 has been significant, impacting both lives and livelihoods. Understanding of the specific signs and symptoms, severe outcomes, and associated medical complications of COVID-19 is still evolving.

Numerous knowledge gaps still exist regarding how COVID-19 and, especially, severe manifestations of the disease impact different sociodemographic and high-risk groups. The recent availability of the much-needed vaccines is very promising. But, how effective are these vaccines on the population at large, and what type of illness will they prevent?

Westat is supporting the Centers for Disease Control and Prevention (CDC) in this research.


Westat has engaged 7 large health systems across the country to use a common protocol and rapidly contribute bi-weekly data from electronic health records (EHRs) and pharmacy outpatient and inpatient records related to COVID-19 testing, vaccinations, illness, and severe outcomes.

Using Amazon Web Services (AWS), we are capturing and harmonizing data in a central database and have instituted procedures for quality assurance and control.

Our statisticians will assist CDC with analyses by comparing groups of people who do and do not get vaccinated and people who do and do not get COVID-19 to assess how well COVID-19 vaccines are working to protect people.


Results from COVID-19 vaccine effectiveness analyses will help CDC learn more about vaccine effectiveness among different populations and over time. Results will further illuminate signs and symptoms associated with COVID-19 illness; who is receiving each vaccine (by age, race, ethnicity, underlying medical conditions); and how different groups respond to the vaccine.

These results will help inform CDC’s recommendations about how people can protect themselves from COVID-19.


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