Supply shortage expected for ProQuad vaccine

Following up on this post from March regarding possible shortages of varicella-containing vaccines, this announcement in MMWR last week alerted readers that Merck's ProQuad (a measles, mumps, rubella, and varicella combination vaccine) would be unavailable beginning in July through at least the end of 2007.

With varicella vaccine limited in supply, Merck is prioritizing production of its stand-alone chickenpox vaccine for children and its new shingles vaccine for adults -- both of which are varicella vaccines -- ahead of ProQuad. With its MMR vaccine still available, no children should go unprotected as a result of this temporary shortage, but an additional injection will be needed to provide full protection against the four infections, as this AP story on the announcement explains.

While this news is more of an inconvenience than a serious concern for physicians or patients, it does illustrate the vulnerability of a system in which a vaccine is produced by a single manufacturer, as is the case for many in the United States.

Potential supply issues for varicella-containing vaccines

Late last month, the CDC's MMWR included a "Notice to Readers" titled "Supply of Vaccines Containing Varicella-Zoster Virus." What are those vaccines? Varivax (against chickenpox), Zostavax (against shingles), and Proquad (a combination of MMR and chickenpox). All are manufactured by Merck, and no other U.S. companies manufacture vaccines providing protection against VZV.

There's no shortage to report, only news from Merck that the yield produced from early stages of the vaccine manufacturing process are less than expected (the reasons for which are not yet known). In the meantime, the plan is to prioritize production of the chickenpox and shingles vaccines, creating the potential for a limited supply of the combination ProQuad by late 2007. Again, not a major issue, as children can receive the same protection by receiving MMR and Varivax separately.

However, this announcement does remind us of the potential fragility of the U.S. vaccine supply. In addition to varicella-containing vaccines, those against measles, mumps, rubella, HPV, and rotavirus, among others, are all produced by a single manufacturer in the U.S. While the economic reasons behind this single-supplier market have been discussed by many, minor hiccups such as this announcement raise the attention of those who worry that the system is not sufficiently insulated against the risk, however small, of major production problems affecting a recommended vaccine.