In a vaccine safety study, routine administration of the quadrivalent HPV vaccine was associated with only two minor short-term adverse events: syncope on the day of vaccination and skin infection during the 2 weeks thereafter, according to a report published online Oct. 1 in Archives of Pediatric and Adolescent Research.
"No other safety signals or potential signals following HPV4 were identified, including hospitalization/ED visits associated with autoimmune conditions" or any of the other categories of adverse outcomes they examined, said Dr. Nicola P. Klein of the Kaiser Permanente Vaccine Study Center, Oakland, Calif., and her associates.
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Researchers say that routine administration of the quadrivalent HPV vaccine was associated with only two minor short-term adverse events—syncope and skin infection.
"These findings support the general safety of routine vaccination with HPV4 to prevent cancer," they noted.
In the retrospective, observational study funded and largely designed by Merck, manufacturer of the Gardasil vaccine, Dr. Klein and her colleagues assessed the short-term safety of HPV4 administered to girls, adolescents, and young women during the course of routine clinical care at two large California HMOs from August 2006 through March 2008. This included all 189,629 females aged 9-26 years who received at least 1 dose of the vaccine during that time, with an additional detailed analysis of the 44,001 females who received all three doses.
All of the study subjects’ hospital and emergency department visits during the 60 days following vaccination were assessed, and the reasons for the visits were categorized according to the Healthcare Cost and Utilization Project’s (HCUP) list of 265 adverse health outcomes. The results for three risk intervals – the day of the vaccine, the 2 weeks following vaccination, and the 60 days following vaccination – were compared with those of a control interval remote from the vaccination date.
In an initial analysis of the data, 50 of these categories showed significantly elevated odds of an association with the vaccine during one or more of these risk intervals. But a detailed review of subjects’ medical records revealed that most of the diagnoses in these categories were present before the vaccine was administered; in other words, they were preexisting conditions. Only syncope and skin infections remained significantly associated with the vaccine after adjustment for these factors.
When the data were further analyzed by vaccine dose, only syncope on the day of vaccination and skin infection during the 2 weeks after vaccination remained significant.
"The association between HPV4 and syncope was not unexpected. Immunization and injections in general have a known association with syncope (particularly in this age group)," Dr. Klein and her associates said (Arch. Pediatr. Adolesc. Med. 2012 Oct. 1 [doi:10.1001/archpediatrics.2012.1451]).
Likewise, some illnesses categorized as "skin infections" may have been local injection-site reactions. But a more detailed review of the subjects’ medical records suggested that there was also a "real" increase in their seeking of medical care for skin conditions following vaccination. The reason for this association remains unknown, but it may be related to the fact that clinical visits in general tend to increase immediately following any injection, the researchers said.
Of note, there were no associations between vaccination and any serious adverse effects such as autoimmune disorders, venous embolism, thromboembolic events, clotting dysfunction, or anaphylaxis, they added.
This study did not address longer-term adverse responses to HPV4 vaccination. Even though the study population was quite large, the study also may have been underpowered to detect extremely rare reactions to the vaccine. "Ongoing monitoring of spontaneous reports and other sources such as the Vaccine Safety Datalink will further contribute to HPV4’s safety profile," Dr. Klein and her associates said.
This study was funded by Merck, which also "provided substantial input into the study design and analytic plan." Dr. Klein reported ties to Merck, GlaxoSmithKline, Pfizer, Novartis, and Sanofi-Pasteur, and a number of the other researchers reported ties to Merck.