Respiratory Syncytial Virus Vaccination Progress

As many parents, teachers, and those working with children could guess, there has been an increase in respiratory syncytial virus (RSV) infections this year causing many clinic and emergency room visits. RSV is one of the most common childhood illnesses. In fact, most people are infected by 2 years of age [1]. The CDC reports that in 2019, RSV accounted for 57,000 hospitalizations, 500,000 emergency department visits, and 1.5 million outpatient clinic visits among children under 5 years of age in the United States alone [2]. RSV globally accounted for 60,000 deaths in children under 5 from RSV in 2015 with infants in the first 6 months of life making up almost half of the deaths [3]. In addition, early childhood infection with RSV has been associated with long-term wheezing, asthma, and impaired lung function. If RSV is wrecking this much havoc, why has a vaccine not been created yet?

RSV has been a particularly difficult virus to create a vaccine for because the early age of infection, the virus’ ability to evade the innate immune system, adaptive immunity unable to prevent reinfection, and the history of vaccine-enhanced disease [4]. A previous trial in the 1960s tested the ability of a killed virus vaccine to produce immunity. The trial revealed an enhancement, or worsening, of the disease rather than prevention of it [5]. Recent studies have shown this enhancement was most likely due to the chemical used to make the vaccine, specifically, to kill the virus.  It caused production of an antibody that did not neutralize the virus, as well as, activation of T-cells that destroyed important cells in the lungs [1,5,6]. Research on a vaccine for RSV was halted for a while because of a fear of similar results. Recent vaccine development has been focused on promoting the production of specific antibodies using a surface protein from the virus rather than using the whole virus itself. Targeting antibody production against the specific surface protein, helps prevent the virus from entering cells and replicating [6]. Studies have also shifted to vaccinating pregnant individuals rather than infants. Since antibodies cross the placenta, babies can receive passive immunity from their mothers rather than having to encounter the vaccine in its entirety. These studies have been largely successful! In November 2022, Pfizer issued a press release indicating positive data from its phase 3 clinical trial testing a maternal RSV vaccine. This vaccine was given to mothers in their late 2nd or 3rd trimester and efficacy against severe medically attended lower respiratory tract illness was measured in the newborns from birth to 6 months. The vaccine was 81.8% efficacious in newborn’s first 90 days which decreased to 69.4% in first 6 months. Pfizer plans to apply for FDA approval before entering phase 4 of the trial [7]. Other clinical trials are exploring the use of mRNA vaccines [3].

This is exciting news! The success of this vaccine brings hope of a decrease in RSV infections, decrease in deaths caused by infection, decrease in long term side effects, and a decreased burden on families and the healthcare system. Hopefully in the future, protective effects of the vaccine will be extended further into childhood. Continue to look out for more vaccine updates!

Shailey is a third-year medical student at the University of Texas Medical Branch and is double majored in Biology and Chemistry at the University of Mary Hardin-Baylor. She is interested in working in pediatrics in the future. 









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