CDC Interim Estimates Find Moderna Vaccines Most Effective Against Delta Breakthroughs

WASHINGTON — Data collected by the Centers for Disease Control and Prevention on COVID-19’s delta variant found that vaccine efficacy was higher among recipients of the Moderna vaccination at 95%, higher than both the Pfizer-BioNTech and the Johnson & Johnson vaccines.

The CDC collected data in a multistate interim analysis of 32,867 medical encounters from a wide range of adults between June and August. In its findings, the CDC found that recipients of the Pfizer vaccine demonstrated 80% effectiveness at preventing breakthrough infection while the J&J vaccine showed 60% effectiveness.

Patients who had not received any COVID-19 vaccine doses were considered unvaccinated, and those who had received one mRNA dose only or their second dose fewer than 14 days before testing or the encounter date were excluded from the study. Out of the adults in the study who experienced emergency department or urgent care visits for “COVID-19–like [illnesses],” positive cases were identified among 7% of fully vaccinated patients and 28.9% of unvaccinated patients.

“[Vaccine effectiveness] was adjusted for age, geographic region, calendar time, and virus circulation, and weighted for inverse propensity to be vaccinated or unvaccinated,” CDC officials said in the report. “[Vaccine effectiveness] estimates with 95% confidence intervals that did not overlap were considered statistically different. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.”

The CDC utilized the “VISION Network” to examine medical encounters from 187 hospitals and 221 emergency departments and urgent care clinics across nine states starting on the date when the delta variant accounted for over 50% of COVID-19 cases in each medical facility’s respective state. Vaccination status of the patients in the study was documented in electronic health records and immunization registries.

The VISION Network is comprised of Columbia University Irving Medical Center in New York, HealthPartners in Minnesota and Wisconsin, Intermountain Healthcare in Utah, Kaiser Permanente Northern California, Kaiser Permanente Northwest in Oregon and Washington, Regenstrief Institute in Indiana and the University of Colorado. The median age of patients in the study was 43 years, and the interquartile range was between 29 and 62 years old.

“The findings in this report are subject to at least three limitations,” CDC officials said in the report. “First, [vaccine effectiveness] by time since vaccination was not examined; further evaluation of possible waning of vaccine protection is currently underway. Second, [vaccine effectiveness] for partial vaccination was not assessed. Finally, although the facilities in this study serve heterogeneous populations in nine states, the findings might not be generalizable to the U.S. population.”

Overall vaccine effectiveness estimates were roughly equivalent to those during the months before the delta variant became predominant in the country, although their effectiveness among adults older than 75 years was lower than adults younger than 75 years. This discrepancy in effectiveness by age “should be interpreted with caution” and could be related to mutations of the virus, waning immunity over the course of time or a combination of factors.

Vaccine effectiveness against emergency department and urgent care clinic encounters overall was 82%, and effectiveness against COVID-19 hospitalization was 86%, according to the CDC’s report. The CDC concluded in its report that further examination of the “magnitude and sources of product-specific” differences in vaccine effectiveness is warranted.

“These findings reaffirm the high protection of COVID-19 vaccines against moderate and severe COVID-19 resulting in [emergency department], [urgent care], and hospital visits and underscore the importance of full COVID-19 vaccination and continued benefits of COVID-19 vaccination during Delta variant predominance,” CDC officials said in the report.