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Is Respiratory Syncytial Virus (RSV) vaccine effective?
At this time RSV vaccine effectiveness is unknown, as effectiveness is based on real-world data of how the vaccine works in the general population and RSV have just been recently licensed and recommended for use in the general population.
However, vaccine efficacy for RSV vaccines is known and based on ideal situations like well-designed clinical trials. Notably, vaccine efficacy can differ from vaccine effectiveness because a vaccine may not work as well in the real world. Understanding what efficacy and effectiveness mean is also important. Below is an example from Yale Medicine.
An example: Imagine there were 100 people in the vaccine group, and 100 people in the placebo group. If 10 people in the placebo group became infected, but only 2 in the vaccine group got sick, that means the vaccine has reduced the chances of illness by 80%; thus, it is considered to have an efficacy of 80%.
Pfizer’s ABRYSVO RSV Vaccine Efficacy
In the pre-licensing clinical trial, Pfizer reported vaccine efficacy to be 66.7 percent against the first episode of RSV-related lower respiratory tract infection with two or more symptoms, and had 85.7 percent efficacy against the first episode of RSV related lower respiratory tract infection with three or more symptoms. The vaccine, however, was reported to have an efficacy of only 33.3 percent in persons with more than one chronic cardiopulmonary condition. Only two RSV related hospitalizations occurred in the clinical trial, both among placebo recipients. A formal evaluation of the vaccine’s efficacy against severe RSV illness was not conducted due to the small number of cases. No RSV-related deaths were reported among trial participants in both the vaccinated and placebo groups.
Preliminary data also reported ABRYSVO’ efficacy to be 62.1 percent against acute respiratory illness. Pfizer, however, failed to complete the analysis of 25.6 percent of swabs submitted for clinical trial participants with acute respiratory symptoms and as a result, the reported vaccine efficacy may be inaccurate.
There is a lack of data on the vaccine’s efficacy against severe lower respiratory tract infection and in persons with immunocompromising conditions and among individuals considered elderly and frail. Data is also lacking on the vaccine efficacy when administrated with other vaccines.
ABRYSVO pre-licensing clinical trials were conducted during the COVID-19 pandemic when rates of RSV illness had significantly decreased, and result in differences between reported efficacy and effectiveness of the vaccine when in use during a season when RSV is circulating at a higher rate.
This vaccine is assumed to offer persistent protection for 7 months but is no longer effective by 24 months.
RSV Vaccine Efficacy in Preventing RSV in Infants
Pfizer reports that the vaccine efficacy in infants born from mothers who received the RSV vaccine during the third trimester of pregnancy was 57.1 percent at 90 days after birth, but waned to 51.3 percent at 180 days and 41 percent at 360 days. Vaccine efficacy for severe RSV was reported at 81.8 percent at 90 days after birth, but waned to 69.4 percent at 180 days. Vaccine efficacy related to hospitalizations were reported to be 67.7 percent at 90 days after birth, but waned to 33.3 percent at 360 days.
GlaxoSmithKline(GSK) AREXVY RSV Vaccine Efficacy
According to GSK, AREXVY RSV vaccine efficacy was reported to be 82.6 percent against the first occurrence of RSV related lower respiratory tract infection in persons 60 through 79 years of age. Data was not sufficient to determine the efficacy of the vaccine in persons 80 years of age and older. Vaccine efficacy in persons with immunocompromising conditions is also unknown.
Based on available data presented during the February 2023 ACIP meeting, vaccine efficacy for the GSK vaccine peaked at two months post-vaccination and by one year, offered no vaccine acquired protection. Additional data provided by the manufacturer during the June 2023 ACIP meeting showed that giving another dose of the vaccine one year later had no impact on boosting the immune response.
RSV Monoclonal Antibody Efficacy
On July 17, 2023, the FDA approved the drug nirsevimab under the trade name Beyfortus, a monoclonal antibody, for the prevention of RSV in infants and children up to 24 months of age. Though the CDC has determined that it can define nirsevimab as a vaccine for their purposes, nirsevimab is not classified as a vaccine by the FDA, American Medical Association or the World Health Organization. To learn about nirsevimab, visit NVIC’s RSV Prevention and Treatment page.
IMPORTANT NOTE: NVIC encourages you to become fully informed about Respiratory Syncytial Virus (RSV) and the Respiratory Syncytial Virus (RSV) vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.