ATLANTA — Postlicensure safety data from the first year of widespread use of Gardasil show that serious adverse events from the quadrivalent human papillomavirus vaccine are rare.
Dr. John Iskander presented the postlicensure data at the June 2007 meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.
The safety data, which encompass the first 11 months of the U.S. experience with Gardasil, were from the United States Vaccine Adverse Event Reporting System (VAERS) and the Vaccine Safety Datalink (VSD), two vaccine surveillance mechanisms supported by the CDC.
The postlicensure data are likely to increase comfort levels for doctors when they talk to patients about the HPV4 vaccine, said Dr. Iskander of the CDC's Immunization Safety Office.
More than 5 million doses of Gardasil have been distributed as of the end of March 2007, according to the vaccine's manufacturer (Merck), although the exact number of doses that have been administered is uncertain at this time.
So far, the HPV4 overall vaccine adverse event reporting rate is 33 per 100,000 doses, and the serious adverse event reporting rate is 1.8 per 100,000 doses, based on VAERS data.
A total of 1,763 adverse events related to use of the HPV4 vaccine had been reported to the VAERS as of May 8, 2007. Of these, 87% involved the use of HPV4 alone. Nearly 70% of the reports involved girls and women aged 9–26 years (the age range used in prelicensure clinical trials).
“A substantial proportion of vaccine events began on the day of vaccination (39%), or in the days [immediately] following vaccination,” Dr. Iskander noted. Similarly, 42% of serious adverse events occurred on the day of vaccination, with an average onset time of 1 day afterward. A total of 857 vaccine events (49%) were reported after a single dose of HPV4.
The most common symptoms in reports of serious adverse events were vomiting (14%), syncope (12%), fever (11%), nausea (11%), and headache (11%). Similarly, the most commonly reported symptoms associated with vaccine use were dizziness (13%), injection site pain (10%), syncope (10%), and nausea (9%).
Although data on associations between HPV4 use and reports of Guillain-Barré syndrome are limited, the VAERS data included 13 reports of GBS in patients who received HPV4. Of these, 11 cases occurred in girls aged 13–16 years; one case occurred in a 50-year-old woman, and the age of the other patient is unknown. More than half of these cases involved coadministration of Menactra and Gardasil.
The VAERS data also included two nonfatal cases of thromboembolism in patients who received the HPV4 vaccine. In addition, 11 serious event reports from VAERS involved syncope, all of which occurred within 10 minutes of vaccination. “Current recommendations suggest a 15-minute waiting period after vaccination … to avoid syncope,” Dr. Iskander noted. Many of the frequently reported adverse events, such as syncope, are common in the general population and do not have a specific relationship to this vaccine or to vaccinations in general, he said.
Dr. Iskander presented details on four cases of death in patients who had been vaccinated with HPV4. None of the deaths appear to be causally related to vaccination, Dr. Iskander said. But the CDC will continue to collaborate with the Food and Drug Administration, the World Health Organization, and other organizations to monitor postlicensure surveillance and other communication related to HPV4.