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Is Respiratory Syncytial Virus (RSV) vaccine effective?
In June 2024, the U.S. Centers for Disease Control and Prevention (CDC) reported vaccine effectiveness of Pfizer’s ABRYSVO and GlaxoSmithKline’s (GSK) AREXVY to be between 73 and 82 percent effective against RSV related hospitalizations in persons 60 years of age and older based on data collected through several U.S. based RSV monitoring systems. The data, however, was reported at 3-4 months post-vaccine administration and not considered sufficient to determine vaccine effectiveness past one season. No vaccine effectiveness data is available for Moderna’s MRESVIA RSV vaccine.
There is no vaccine effectiveness data on the use of Pfizer’s ABRYSVO RSV vaccine in pregnant women due to low vaccine uptake, the timing of RSV vaccine availability, and the early onset of the RSV season in 2023 – 2024.
Pre-licensing clinical trials of all RSV vaccines evaluated vaccine efficacy, not vaccine effectiveness. Vaccine effectiveness is based on real-world data of how the vaccine works in the general population, which is not available until after the product is widely used in the target population.
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%.”
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.
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 not considered to have any effectiveness by 24 months.
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.
According to Moderna, at 3.7 months following administration, MRESVIA RSV vaccine efficacy was reported to be 78.7 percent against RSV illness with two or more symptoms of lower respiratory tract disease (LRTD), and 80.9 percent against RSV illness with three or more symptoms of LRTD. At 8.6 months following administration, MRESVIA RSV vaccine efficacy was reported to be only 62.5 percent against RSV illness with two or more symptoms of LRTD, and 61.1 percent against RSV illness with three or more symptoms of LRTD.
At 8.6 months following vaccine administration, MRESVIA RSV vaccine was reported to have an efficacy of 58.8 percent in persons 60 through 69 years of age, and an efficacy of 78.0 percent in person 70 through 79 years of age. In persons 80 years of age and older, by 8.6 months, MRESVIA RSV vaccine was reported to have an efficacy of -20 percent. A negative efficacy means that individuals who received MRESVIA were more likely to develop RSV than those who received the placebo.