RSV Vaccine: Not Just for Kids?

[[{"type":"media","view_mode":"media_crop","fid":"49729","attributes":{"alt":"","class":"media-image media-image-right","id":"media_crop_5126144715685","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"6041","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"height: 180px; width: 265px; float: right;","title":"©chrupka/Shutterstock.com","typeof":"foaf:Image"}}]]For decades after its discovery in 1956, respiratory syncytial virus (RSV) was thought to be a problem only for children. Over the last several decades it has become apparent that RSV is a major problem in the adult population as well, particularity among the elderly and immunocompromised. RSV is now thought to be responsible for 2-5% of adult community acquired pneumonias. Adult nursing homes, like child day care facilities, are good set ups for disease transmission.

How do you think the estimated annual attack rate of RSV disease in nursing homes compare with the annual attack rate for non-pandemic influenza?

A. About the same, 5-10% in most years

B. About twice as much flu as RSV 

C. About 3 times more flu than RSV

D. About twice as much RSV as flu

Click here for answer and discussion.

Answer: A. About the same, 5-10% in most years

Some researchers feel the impact of RSV on the elderly is comparable to the havoc wrought by non-pandemic influenza with attack rates of 5-10% a year in nursing home settings setting the stage for a  10-20% pneumonia rate and a 2-5%  death rate. Symptoms of adult RSV and influenza infections are similar: runny nose, cough, fever, and wheezing.

While reinfection is common throughout life, there is evidence that at least partial immunity can be induced through both the humoral and cellular component of the immune system. Several live vaccines against RSV are being tested; one is about to begin phase 3 testing. Live vaccines are much more likely to induce both humoral and cellular immune responses. Inactivated vaccines tend to work only through antibody production. In addition, a previous inactivated vaccine tried in 1966 in children not only didn't work, but actually caused increased severity of disease in RSV-infected infants.

Since a single natural infection does not induce great immunity, multiple doses of an RSV vaccine will likely be needed.

The pediatric age group most likely to be hospitalized with RSV infection is infants younger than 6 months of age. Since a single natural infection does not induce great immunity, multiple doses of an RSV vaccine will likely be needed. A better approach might be to do what we are now doing to protect young infants against pertussis and influenza: maternal immunization. The CDC recommends Tdap and inactivated flu vaccine for all pregnant women, preferably in the third trimester. Two potential hurdles for the maternal-immunization-to-protect-the-newborn approach:  no live vaccine is currently approved for use in pregnancy and maternal transmission of antibodies to the fetus takes place later in pregnancy, leaving babies born very premature relatively unprotected due to lack of maternal antibodies.

What does the future hold? I suspect we will need several vaccines. A live attenuated one can be given to infants like we do with the attenuated live rotavirus vaccines. By inducing both IgA and IgG production, it may work better than an inactivated vaccine. I doubt that big pharma will want to test live vaccines in pregnant females since any birth defect (with a natural background rate of about 1%) will likely lead to law suits even though RSV infections in pregnant females have not been shown to cause an increased rate of malformations in the fetus. A non-live vaccine would be needed for pregnant moms as well as the immunosuppressed.

Like the “silly wabbit” of television commerical fame who would love to get his hands on someTrix cereal, I can't wait for the development of one or more RSV vaccines including at least one that is not “just for kids.”

Resources

A look at RSV infections in adults:

Falsey AR, Walsh EE. Respiratory Syncytial Virus Infection in Adults. Clin Microbiol Rev. 2000;13: 371–384.

 An overview and listing of the 51 RSV vaccines being researched:Status of vaccine research and development of vaccines for RSV. Prepared for WHO PD-VAC. Date submitted: June 30, 2014.