Dec. 13, 2010 - Only about one in seven girls who start the human papillomavirus (HPV) vaccine series finish the three-shot sequence on time, according to a new study.
But the study found that only 14% of girls aged 9 to 26 who started the HPV vaccine series completed it within seven months, and 28% received all three HPV shots within a year. The HPV vaccine is given in three doses, with two months between the first and second doses and six months between the first and third dose.
Researchers say those completion rates are much lower than previously reported from the CDC and suggest that many young women are unprotected or underprotected from the most dangerous strains of the sexually transmitted virus.
"Low vaccine completion rates and/or prolonged intervals between doses may be a problem," researcher Lea E. Widdice, MD, of Cincinnati Children's Research Foundation, and colleagues write in Pediatrics. "The duration of protection and efficacy offered by incomplete immunization or immunization at intervals different from that of the clinical trials are currently unknown."
Low Completion Rate May Affect Cervical Cancer Disparities
The study followed 3,297 females, 67% black and 29% white, who started the HPV vaccine series within two years after a vaccine became available from one medical center in Cincinnati, Ohio, from November 2006 to June 2008.
The results showed that less than 3% of the HPV shots were received earlier than recommended but more than 50% of doses were received late.
Fourteen percent completed the HPV vaccination series within a sevenmonth period, and 28% by 12 months.
Researchers say whites were twice as likely as blacks to complete the HPV vaccination series by seven months, which "raises concern that disparities in vaccine completion could exacerbate existing disparities in cervical cancer."
Other factors that increased the likelihood of HPV vaccine completion were having private vs. public health insurance and using contraception that required a shot every three months at a medical care provider.
The authors note that their findings may not represent other populations and that information about other factors that could influence vaccination such as adverse side effects were not available.