Notes from the Field: Expired Influenza Vaccines
In what will undoubtedly be ammo for the antivaxxer movement, the latest issue of Morbidity Mortality Weekly Report from the CDC reports the ongoing surveillance of vaccine administration for seasonal influenza is not perfect. The seasonal influenza vaccine comes in two forms: an inactivated virus formulation that is injected, and a live, attenuated virus formulation that is administered nasally. Both forms of the vaccines are generally widely available in late summer/early fall, and are recommended for the general population of the US for everyone over the age of 6 months. The inactivated vaccine has an expiration date of June of the following year, and is contraindicated for use at that time, mainly because of the lack of protection that it will offer to novel influenza strains that will have arisen by that point. The live attenuated vaccine on the other hand has an expiration date of about 18 weeks (4.5 months), and should be disposed of at that point even if the flu season is still going on. Since the flu season generally runs from November through March, it generally should not expire during this time, however if the vaccine is produced but not administered earlier in the season, stockpiles of expired vaccine may accumulate.
Epidemiologists from the CDC analyzed data from the national Vaccine Adverse Event Reporting System (VAERS), from 2007 through 2014. Of reports using live virus vaccines, approximately 18% of those reports indicated that expired vaccine had been administered to patients, and the vast majority of those reports did not document any adverse health events. The most likely outcome due to administration of any expired vaccine is a lack of protection against season flu. Consequently, revaccination with a valid dose is recommended to maintain protection against flu. The CDC recommends that all health care providers be aware of the significantly shorter shelf life of the live vaccine, and to be aware of return and replacement options from vaccine manufacturers.