Is RSV a new virus? How serious is RSV?
The respiratory syncytial virus has been known for decades to cause serious disease in very young children. Most children will have had a RSV infection in their first few years of life. Most of the time an RSV infection will result in mild illness - often resembling a bad cold. The percentage of RSV infections that result in hospitalizations is very low. However since almost all children will get RSV, the virus causes a significant number of hospitalizations and deaths in children.
In the United States annually there are an estimated 58,000-80,000 hospitalizations among children younger than 5 years old. RSV kills about 100–300 children younger than 5 years old each year. Children with chronic health problems are more likely to be hospitalized with RSV infections. However the majority of kids that are hospitalized were previously healthy (as is the case with young children hospitalized with COVID-19). Stated in another way chronic health problems such as diabetes and heart problems place a child at higher risk for being hospitalized with RSV infections, however previously healthy young children are at significant risk from being hospitalized with an RSV infection or with COVID-19.
RSV has increasingly been recognized as a cause of serious illness in older adults. This may be because the tests used to detect RSV have become more widely used. An estimated 60,000-160,000 hospitalizations occur annually in the US among adults 65 years and older with 6,000-10,000 deaths each year.
Why did it take so long to develop a vaccine against RSV?
Attempts to make a vaccine against RSV started way back in the 1960’s. A major roadblock to the development of RSV vaccines has to do with the structure of the vaccine’s target. The target of the RSV vaccines is a viral surface protein referred to as the fusion protein (F protein). This protein is involved with the entry of the virus into our cells. The problem had been that the protein was not stable and would change configuration. In 2013 a process was developed to “freeze” the protein into it’s pre-fusion configuration. To learn more about this science watch this video (fast forward to about the 11 minute mark).
In the video researcher Barney Graham discusses how the protein changes and that causes an important epitope to be lost. The concept of an “epitope” is extremely important to understanding how our immune system works and how vaccines are developed. An epitope is a small portion of the virus (or other pathogen) that the immune system recognizes. The body does not recognize the whole virus, just small pieces of viral proteins. Click here for a short video describing an epitope visually.
What are the RSV vaccines approved for older adults?
There are two RSV vaccines approved for adults ages 60 years and older Arexvy (GSK) and Abrysvo (Pfizer). Both vaccines are recombinant protein vaccines that cause the immune system to produce antibodies and cellular responses to the viral cell surface protein that is key to the virus entering our cells. Both are currently approved as a single dose and were shown in clinical trials to protect against symptomatic lower respiratory tract disease caused by RSV in adults ages 60 and older, with more than 80% percent efficacy in the first RSV season after vaccination. GSK’s vaccine includes an adjuvant (the same adjuvant used in GSK’s recombinant zoster vaccine [Shingrix]), which is a component that is intended to enhance the immune response to vaccination. Pfizer’s vaccine does not contain an adjuvant. There are no head to head trials to compare these vaccines.
How does vaccination during pregnancy help protect babies during their first months of life?
The RSV vaccine Abrysvo given as a single injection sometime between the 32nd and 36th week of pregnancy will stimulate an antibody response against the virus. These antibodies (and others) pass through the placenta to the baby. After birth the antibodies will persist for a few months providing the baby with a head start on the virus when infected. This is considered to be a form of “passive immunization”.
How does the RSV immunizations for children 19 months and younger work?
Nirsevimab (Beyfortus) is an immunization recommended for infants younger than 8 months of age who are born during—or who are entering—their first Respiratory Syncytial Virus (RSV) season. Nirsevimab is also recommended for some children aged 8 through 19 months who are at increased risk for severe RSV disease and entering their second RSV season. This is a “passive immunization” in that the baby’s immune system is not directly stimulated. The injection is of already formed antibodies against the virus. The antibodies last around 5 months from a single injection providing a level of protection against severe disease during the peak of the RSV season. This immunization is currently in short supply therefore use is being restricted to those at highest risk in areas where the product is in short supply. Visit with your child’s primary care provider for more details. Children younger than age 24 months of age with certain conditions that place them at increased risk for severe RSV disease may receive another monoclonal antibody product: palivizumab (Synagis). It must be given once a month during RSV season.
References for “Tis the Season for Respiratory Illnesses”: RSV
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