The controversial Gardasil vaccine from Merck & Co. that prevents cervical cancer in girls has been met with fainting and complaints of prolonged pain, already gaining a reputation as the most painful childhood shot, experts say.

Gardasil, produced by Merck & Co., targets the human papilloma virus (HPV), a sexually transmitted virus which causes cervical and vaginal cancer. Health officials have promoted the product as an important new protection against the diseases.

The Food and Drug Administration approved it for girls ages 9 to 26 in the summer of 2006.

During its first year of use, the Gardasil vaccine was frequently associated with fainting, particularly among teenagers, however it is not yet clear whether the pain of the cervical cancer vaccine was the reason for the reaction.

“This vaccine stings a lot,” Patsy Stinchfield, an infectious disease expert at Children's Hospitals and Clinics of Minnesota, was quoted by the Associated Press as saying during a recent meeting of vaccination experts in Atlanta.

Stinchfield seems to mirror the feelings of numerous girls who have taken the shot. There have been complaints that the pain of this particular vaccine, which comes in a three-dose package, is prolonged. While other shots tend to hurt only as the needle pricks the skin, the cervical cancer vaccine can cause pain in the arm for up to a day after getting the shot.

Reactions when receiving the vaccine are mixed, according to reports. Some girls only wince, others complain of extended discomfort while others have even fainted.

Merck & Co. officials explain that the pain may be due to the virus-like particles in the shot, reports the AP. Pre-marketing studies showed more reports of pain from Gardasil than from dummy shots; shots containing more of the particles were associated with reports of more pain.

As to the passing out, U.S. health officials say there has been a rise in reports of vaccine-associated fainting in girls.

While some 50 reports of fainting were reported between 2002 and 2004, from 2005 until July 2007 there were about 230. More than half of these cases occurred after a shot of Gardasil.

There is no evidence yet that the pain associated with a Gardasil shot is related to the fainting.

Dr. Barbara Slade, an immunization safety specialist at the U.S. Centers for Disease Control and Prevention, was quoted by the AP as explaining that fainting seems to have a greater frequency among teenagers, quite inexplicably. Scientists speculate that one reason could be the characteristic nervousness of this age group.

While Merck & Co.’s Gardasil is at the moment the only vaccine approved specifically to target the human papilloma virus, a competitor is soon to be released on the market: GlaxoSmithKline's Cervarix, currently under FDA review and possibly available sometime in 2008.