Phase 3 Study Initiated for Pfizer mRNA-Based Influenza Vaccine


Quadrivalent mRNA influenza vaccine candidate to be evaluated in approximately 25,000 healthy US adults.

The first participants have been dosed in a pivotal phase 3 clinical trial to evaluate the efficacy, safety, tolerability, and immunogenicity of Pfizer’s quadrivalent modified RNA (mRNA) influenza vaccine candidate in approximately 25,000 healthy US adults. The phase 3 study is updated by previously shared data from the ongoing phase 2 trial.

The phase 2 trial has demonstrated a safety and immunogenicity profile supportive of program advancement and focuses on using mRNA technology to help protect against the flu. Further, Pfizer has ongoing studies exploring other novel mRNA technology, such as self-amplifying RNA, which has the potential to provide more benefits.

“For years, there has been a need to better address the burden of influenza, despite the use of existing seasonal flu vaccines. Our experience with RNA viruses and mRNA technology has given us an even deeper understanding of the opportunity to potentially provide more efficacious vaccines that could further reduce the yearly rates of the severe outcomes of viral disease like flu, including hospitalization and death,” said Annaliesa Anderson, PhD, senior vice president and chief scientific officer, Vaccine Research and Development at Pfizer, in a press release. “We are excited to start the first phase 3 efficacy study of an mRNA-based influenza vaccine that could potentially deliver an improved flu vaccine to help address the significant burden of this disease.”

Although currently available vaccine strains are similar to circulating influenza viral strains, the vaccines typically only provide 40% to 60% protection, with lower protection observed in recent years because of poor matching of strains, according to Pfizer. The flexibility of mRNA technology and rapid manufacturing could improve strain matches in the future, because mRNA-based influenza vaccines require only the genetic sequence of the virus.

The flu causes between 140,000 and 710,000 hospitalizations, 12,000 and 52,000 deaths and approximately $25 billion in economic loss in the United States each year. The virus has been found to have an even greater impact on racial and ethnic minority groups in the United States.

According to Pfizer, Black Americans have a 1.8 times greater risk of hospitalization from the flu vs white counterparts, whereas Latino and Indigenous Americans have a 1.2- and 1.3-times greater risk of hospitalization, respectively. Vaccination for the flu is among the most effective ways of preventing infection and serious illness; however, racial and ethnic minority communities in the country continue to be immunized at lower rates.

Pfizer noted that clinical trial enrollment for new or improved vaccines typically lack diversity. As such, the manufacturer announced a commitment to help lower health disparities via clinical trials with study populations that are representative of the racial and ethnic diversity of the regions in which the trials are conducted.


Pfizer Initiates Phase 3 Study of mRNA-Based Influenza Vaccine. Pfizer. September 14, 2022. Accessed September 16, 2022.

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