Identification of Rare Adverse Events with Year-varying Reporting Rates for FLU4 Vaccine in VAERS.

In 2012, a new influenza vaccine - FLU4 was first licensed in the US. FLU4 is a quadrivalent flu vaccine, which can protect against four flu viruses. Compared to FLU and FLU3, FLU4 gives broader protection against the flu viruses. To our knowledge, few studies have focused on the FLU4 vaccine and its adverse events. Since safety signal detection is important in vaccination, it is necessary to launch such studies on FLU4. In this paper, we used the Vaccine Adverse Event Reporting System (VAERS), which is a national post-marketing vaccine safety surveillance program to identify rare adverse events with year-varying reporting rates for FLU4. The differences in the reporting rates over years are potential signals of vaccine safety issues caused by updates of FLU4 ingredients. We used a likelihood ratio test to simultaneously test the sparsity of events and the differences of event rates over years. We identified 4 adverse events that are rare and have significantly different reporting rates over years.