|Articles|September 16, 2021

Vaccines Remain Effective Against Delta

Recent data shows that all three COVID-19 vaccines being administered in the United States are showing high rates of vaccine effectiveness (VE).

The Centers for Disease Control and Prevention (CDC) has released data showing the three vaccines (Pfizer-BioNTech, Moderna, and Janssen [Johnson & Johnson]) being administered in the United States are demonstrating a high level of VE, especially against severe infection.

“VE of all three authorized COVID-19 vaccines combined remained high against hospitalization (86%) and ED/UC encounters (82%),” The CDC wrote in its Morbidity and Mortality Weekly Report.

The data comes from reporting done using 32,867 medical encounters in 187 hospitals and 221 emergency departments (ED) and urgent care clinics (UC) in 9 states from June through August. This began on the date the Delta variant accounted for 50% of sequenced isolates in each medical facility’s state.

The study demonstrates the value of vaccination during the Delta surge this summer.

“Among adults with ED/UC encounters for COVID-19–like illness (18,231; median patient age = 43 years, IQR = 29–62 years), laboratory-confirmed SARS-CoV-2 infections were identified among 28.9% (3,145 of 10,872) of unvaccinated and 7.0% (512 of 7,359) of fully vaccinated patients,” the CDC wrote.

Interestingly, there was some significant statistical differences in the effectiveness of the different vaccines. “VE was highest among Moderna vaccine recipients (92%), followed by Pfizer-BioNTech vaccine recipients (77%), and was lowest (65%) for Janssen vaccine recipients.”

The authors did report 3 limitations in their study, specifically, VE by time since vaccination was not examined; VE for partial vaccination was not assessed; and the findings might not be generalizable to the US population.

“These findings reaffirm the high protection of COVID-19 vaccines against moderate and severe COVID-19 resulting in ED, UC, and hospital visits and underscore the importance of full COVID-19 vaccination and continued benefits of COVID-19 vaccination during Delta variant predominance,” the CDC concluded in its report.


Related to this article

Measles Update: October 30, 2026
The latest CDC numbers show a 5.8% increase in measles cases from week-to-week, bringing the 2026 US total to more than double the amount seen in all of 2025 with 2 months left in the year.
Cefiderocol Continues to Show Activity Against Resistant Gram-Negative Infections
Shionogi data presented at IDWeek 2026 demonstrated a 76.7% clinical response with cefiderocol in carbapenem-resistant respiratory infections and high in vitro activity against resistant P aeruginosa VAP isolates. Christine Slover, PharmD, vice president, Infectious Diseases US Medical Affairs, Shionogi, offers insights on the data as well as clinical considerations for providers when weighing the antibiotic for patients.
FAQ: Shamonda Virus
As France confirms the first documented human Shamonda virus infection, a fatal encephalitis in a stem cell transplant recipient, this FAQ explains what the virus is, where it has spread, how the case was diagnosed, how the patient was likely infected and what clinicians should watch for.
ID Week Highlights Part 1
In this first IDWeek 2026 roundup, oral olorofim matched AmBisome in invasive aspergillosis, aztreonam-avibactam held activity as MBL-producing CRE rose, pritelivir cut hospitalizations in refractory HSV, and zelicapavir shortened RSV symptoms in high-risk adults.