Production of vaccine is down

Young children needing immunization against chickenpox and three other diseases probably will have to get an extra shot because of manufacturing problems that have cut production of a four-disease combo vaccine made by Merck & Co.

Merck said that its ProQuad vaccine, which protects against measles, mumps and rubella as well as chickenpox, won’t be available from about July until at least year’s end.

However, the drug maker expects to have plenty of two separate vaccines that cover the same diseases: Varivax, for chickenpox, and M-M-R II, for measles, mumps and rubella.

The federal government recommends children get each of those shots twice, once at age 12 months to 15 months and again between ages four and six years old, or -- when available -- they can receive the ProQuad vaccine twice.