A Potential Breakthrough in the Fight Against RSV? Pfizer’s Vaccine Candidate Enters Phase 3 Trials

Every fall, the classic symptoms appear as the temperature drops. A runny nose. Coughing. Sneezing. A fever.1

By the time spring arrives, millions of Americans will have been sickened by illness caused by Respiratory Syncytial Virus (RSV). Most people get over a mild illness in a week or two. But each year, approximately 177,000 adults 65 years and older go to the hospital after contracting the virus, and it is estimated that14,000 die, according to the U.S. Centers for Disease Control and Prevention.2

There is no approved vaccine to prevent RSV today. But, in early September, Pfizer began a Phase 3 clinical trial to evaluate the efficacy, immunogenicity and safety of a single-dose of its investigational vaccine candidate, known as RSVpreF, in adults 60 and older.

Around 30,000 people around the world will participate in the trial to see if the investigational vaccine can help to prevent moderate to severe lower respiratory tract illness.

Dr. Albert Bourla, Pfizer’s chairman and CEO, said the company’s goal is “to build upon [past] successes by continuing to follow the science, trust in our people and remain focused on delivering breakthroughs for the patients we serve.”

Data from a Phase 2a challenge study

Results from an earlier trial of the RSVpreF investigational vaccine candidate in healthy adults 18 to 50 years were “overwhelmingly positive”, according to Mikael Dolsten, the company’s chief scientific officer.3

In the Phase 2a challenge study, the investigational candidate was 100% effective against mild-to-moderate symptomatic infection in the 62 participants, Dolsten said. Most study participants experienced minimal to no side effects. Importantly, the investigational candidate was also very good at neutralizing both of the virus subtypes that infect humans.

An opportunity to protect infants

A separate Phase 3 trial of the RSVpreF vaccine in pregnant women aged 18 to 49 started in June 2020, with the goal of helping to protect their babies in the first weeks of life.4

Research has shown maternal vaccination can result in the transfer of antibodies through the placenta, which then helps protect the baby.

“[You vaccinate] the mom to boost her immunity, and as a result, you’re actually helping to protect the infant too,” said Dr. Iona Munjal, director of Pfizer’s Vaccine Research Unit.5

RSV is the leading reason infants less than a year old go to the hospital.<sup6 In a single year, researchers estimated that RSV caused more than 33 million acute lower respiratory infection cases globally, 3.2 million hospital admissions, and nearly 60,000 hospital deaths in children five years and younger, according to a review published in The Lancet.7

Taken together, the RSV vaccine studies in pregnant women and older adults address an important unmet medical need.

“The start of this Phase 3 study is an important step forward towards our goal of comprehensive immunization against RSV disease, which includes developing a potential first vaccine to help prevent RSV disease in adults as well as the ongoing efforts to help protect infants through maternal immunization,” said Kathrin Jansen, Pfizer’s Senior Vice President and Head of Vaccine Research & Development.

[1] CDC.gov. Respiratory Syncytial Virus Infection, Symptoms and Care. Available here.
[2] CDC.gov. Respiratory Syncytial Virus Infection, Trends and Surveillance. Available here.
[3] Q2 2021 Pfizer Inc. Earnings Call. Available here.
[4] Pfizer Announces the Start of Four Phase 3 Clinical Trials for Investigational Vaccines. Available here.
[5] Ozy. The Next Frontier in Vaccines: Maternal Immunization. Available here.
[6] Journal of Perinatology. Respiratory syncytial virus hospitalization outcomes and costs of full-term and preterm infants. Available here.
[7] Global, regional, and national disease burden estimates of acute lower respiratory infections due to respiratory syncytial virus in young children in 2015: a systematic review and modelling study. Available here.

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