Tracking vaccine lot lifecycles using reports to the vaccine adverse event reporting system (VAERS)

There is currently no systematically available information available on how rapidly a specific lot of vaccine is used once distributed. We used data from reports to the Vaccine Adverse Event Reporting System (VAERS) to develop a proxy means of surveillance for the lifecycle of selected vaccine lots.

A convenience sample, consisting of selected lots of: diphtheria, tetanus, and acellular pertussis (DTaP), Haemophilus influenzae type b (Hib), Hepatitis B, and varicella vaccines, was selected for lifecycle analysis. Assuming that circulation of a vaccine lot is proportional to vaccine-specific adverse event (AE) reporting for that vaccine type, we constructed Gamma distributed usage models and compared them with lot-specific VAERS reports to estimate the actual lifecycle of lots in the system.

Evidence of lot circulation was detected within 1-2 months, and a peak was observed 3-4 months after the vaccine release date for most of the study vaccines. Ninety percent of the vaccine doses in each lot were estimated to be used within 5-9 months of distribution. The length of time a vaccine lot was in use ranged from 5 to 17 months from earliest vaccination date.

Our modeled and inferred administration of the selected lots of different vaccines were concordant. This method may be useful for spatial and temporal tracking of vaccine lot utilization.