Expert Interview

Elizabeth Rowley Discusses Latest Data on Vaccine Effectiveness Against the Delta Variant

September 10, 2021

In the summer of 2021, when the Delta variant became the predominant coronavirus strain sweeping the country, there was limited data regarding COVID-19 vaccine effectiveness to combat it. More data were needed and quickly. The Centers for Disease Control and Prevention (CDC) charged Westat with capturing, unpacking, and analyzing data supplied through the CDC-funded VISION Network of integrated care and health systems using data from a 2-month time period. The task of analyzing the data fell to Westat’s Elizabeth Rowley, Dr.P.H., a senior biostatistician. Here she discusses her work, key findings, and the forthcoming article on those discoveries.

Elizabeth Rowley

Q. Dr. Rowley, can you describe the process of collecting and analyzing the data?

A. In June and July, when the Delta variant became predominant, our VISION Network team at Westat collected data from 30,000 patient encounters at 187 hospitals and at 221 emergency departments and urgent care clinics in multiple states. The patients presented with COVID-like illnesses and ranged in age from 18 to 75+. Their vaccination status was documented in electronic health records (EHRs) and immunization registries. All of this information was supplied by the VISION Network. The odds of COVID-19 infection were compared between those fully vaccinated and those unvaccinated using a test-negative design.

Q. What were the key findings?

A. We found that the COVID-19 vaccines are still efficacious against the Delta variant. However, vaccine effectiveness against hospitalization was significantly higher among Moderna recipients (95%) compared to Pfizer recipients (80%) and Johnson & Johnson recipients (60%). In older, fully vaccinated adults, aged 75 and older, the effectiveness was less than in younger adults (89% vs. 76%). Similar trends by vaccine type were seen in vaccine effectiveness against emergency department and urgent care visits (Moderna 92%, Pfizer 77%, and Johnson & Johnson 65%).

Q. What was your role in this work?

A. This was a tremendous effort by many including our Westat VISION team and our CDC colleagues. I worked with a biostatistician at CDC who designed the study, and I was able to provide input in the beginning. With help from others on the Westat team, I designed the code and built the structure of the analysis so that I could rapidly rerun the analyses every 2 weeks, while also building in flexibility to extend to further analyses by using the same chunk of code. CDC wanted us to use a functionality particular to the R statistical analysis software—a program with which I am very experienced. This work used propensity scores to estimate vaccine effectiveness and to ensure the vaccinated and unvaccinated patients were comparable.

Q. How fast was this analysis conducted?

A. Very fast. I had to analyze a new batch of data from multiple sites every 2 weeks, and the data set kept growing. We are answering a critical public health question. The time pressure was enormous.

Q. You used EHRs to support this research. What were their benefits and drawbacks?

A. EHRs are essential to rapidly gathering and harmonizing patient data across diverse populations; these data also allow for the examination of rare outcomes. One issue in working with EHR data is that not all diagnoses are necessarily recorded in the same way, and sometimes different EHR systems follow different workflows for recording medical information in the EHR. Working closely with our network partners and CDC colleagues, we were able to determine a meaningful common set of information that could be provided to the CDC in a uniform and useable format.

Q. How helpful are these findings?

A. Our findings add one more important piece to the puzzle surrounding vaccine effectiveness and the Delta variant, but much more work needs to be done.


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