Vaccine Safety

Human Papillomavirus (HPV) Vaccine

Every year in the United States, about 11,000 women are diagnosed with cervical cancer and almost 4,000 die from this disease. Most cases of cervical cancer and all cases of genital warts are caused by human papillomavirus (HPV). There are two HPV vaccines available to protect against the types of HPV that cause most cervical cancers. Both vaccines are usually given as a 3 shot series. Clinical trials and post-licensure monitoring data show that both vaccines are safe.

Based on information available today, CDC continues to recommend HPV vaccination for the prevention of most types of cervical cancer. As with all approved vaccines, CDC and Food and Drug Administration (FDA) will continue to closely monitor the safety of HPV vaccines. Any problems detected with these vaccines will be reported to health officials, health care providers, and the public. Needed action will be taken to ensure the public’s health and safety.

Currently, there are two licensed HPV vaccines in the United States available to protect against the types of HPV infection that cause most cervical cancers:

Cervarix: FDA licensed Cervarix in 2009. This vaccine is recommended for females 10 through 25 years of age. The safety of Cervarix was studied in clinical trials with over 30,000 females before it was licensed. Cervarix protects females against HPV types 16 and 18. To learn more about Cervarix, visit FDA.
Gardasil: FDA licensed Gardasil in 2006. Gardasil is recommended for 11- and 12 year-old girls, and also females 13 through 26-year-old who were not previously vaccinated. Gardasil is also recommended for 9- through 26- year-old males to protect against some genital warts. The safety of Gardasil was studied in clinical trials with over 29,000 females and males before it was licensed. This vaccine protects females against HPV types 6, 11, 16, and 18. To learn more about Gardasil, visit FDA.

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How CDC Monitors HPV Vaccine Safety

Vaccines continue to be monitored for safety after they are licensed. This is because pre-licensure trials are often too small to detect rare events and special populations may not be adequately represented. Since licensure, CDC and FDA have been closely checking the safety of HPV vaccines through 3 monitoring systems. These systems can monitor adverse events (health problems) already known to be caused by vaccines, as well as detect rare adverse events that were not identified during pre-licensure clinical trials. The 3 systems are:

The Vaccine Adverse Event Reporting System (VAERS)–an early warning public health system that helps CDC and FDA detect possible side effects or adverse events following vaccination.
The Vaccine Safety Datalink (VSD) –a collaboration between CDC and several health care organizations which monitors and evaluates adverse events following vaccination.
The Clinical Immunization Safety Assessment (CISA) Network– a collaboration between CDC and medical research centers in the U.S. which conduct research on adverse events that might be caused by vaccines.

A Closer Look at the Safety Data

VAERS
In 2009, a CDC-FDA report analyzed adverse events reported to VAERS following Gardasil vaccination from June 2006 through December 2008. This post-licensure study included clinical review of medical records associated with reports to VAERS. The findings were similar to what is seen in the safety reviews of other vaccines recommended for a similar age group, 9 to 26 years old.

The most common adverse events reported were:

Syncope (or fainting)–common after receiving shots, especially in pre-teens and teens
Local reactions at the site of immunization (pain and redness)
Dizziness
Nausea
Headache

There was increased reporting of syncope and venous thromboembolism (VTE), or blood clots, compared with what has been found for other vaccines given to females of the same age. Of the people who had blood clots, 90% had a known risk factor for them, such as smoking, obesity or taking oral contraceptives (birth control pills).

Post-licensure safety monitoring from June 2006 through March 2012 continues to show no new HPV vaccine safety concerns.

VSD
In 2011, VSD active surveillance (called Rapid Cycle Analysis) looked at specific adverse events following more than 600,000 doses of Gardasil, such as Guillain–Barré Syndrome (GBS), stroke, VTE, appendicitis, seizures, syncope, allergic reactions, and anaphylaxis. No statistically significant increased risk for any of these adverse events was detected after vaccination.

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