Merck & Co. sells Zostavax, a shingles vaccine that contains about 14-times more live virus than Varivax, a chickenpox vaccine that is given to children.
The viruses are weakened (attenuated), usually causing a mild infection in healthy patients. This mild infection triggers the immune system to respond, fight off the virus, and develop immunity to prevent shingles.
Life-threatening infections occur when the immune system is too weak to fight off the virus. Zostavax is not safe for people who have weak immune systems or conditions like leukemia, lymphoma, AIDS, and cancer.
Zostavax is also not safe for people who are on medications that prevent activity of the immune system, such as steroids or anti-rejection drugs.
The Australian Therapeutic Goods Administration (TGA) said patients may not be able to get Zostavax if they have certain health problems or they are taking medicine that affects the immune system.
The TGA also reminded doctors not to give Zostavax to these patients:
Health professionals should carefully consider a patient’s immunological status prior to vaccination and not administer Zostavax in immunodeficient or immunosuppressed patients. If unsure, defer vaccination and seek specialist advice.”
The good news is that patients might soon have an alternative. Merck is in Phase III clinical trials for a new shingles vaccine that contains an inactivated virus rather than a live virus. It was developed specifically for adults over 18 with compromised immune systems.
Many people are surprised to learn that Zostavax can cause shingles or chickenpox, the exact same diseases it is supposed to prevent, although infections tend to be a lot less serious in people who get the vaccine.
Merck is facing lawsuits for failing to warn that Zostavax can cause chickenpox or shingles after the shot. Zostavax has been sold since 2006, but Merck did not add these side effects to the label until December 2014. Merck also strengthened warnings about “infections and infestations” with the virus in the vaccine.
Source: Zostavax Vaccine Safety Advisory