Getting children to comply with a three-dose series of vaccines is difficult, in both rich and poor countries.
A new study coauthored by University of New Mexico researchers suggests that a single dose of the vaccine Cervarix offers women as much protection as the recommended three-dose series from two types of human papillomavirus, or HPV, that cause 70 percent of deaths from cervical cancer.
The finding could have important implications because vaccinating children with a single dose of HPV vaccine is easier than getting them to comply with a three-dose series, said Cosette Wheeler, lead author of the study published in the June 8 online edition of the journal Lancet Oncology.
HPV is a common virus spread by sexual activity. The U.S. Centers of Disease Control and Prevention recommends that boys and girls receive HPV vaccinations at age 11 or 12, allowing them to develop immunity before they become sexually active.
Women can get the HPV vaccine through age 26 and men through age 21. The vaccine now is given in a series of three shots over six months.
Two types of human papillomavirus – HPV types 16 and 18 – cause 70 percent of cervical cancer deaths.
Cervical cancer is the leading cause of cancer deaths among women worldwide. HPV-related cancers strike about 17,000 women and 9,000 men each year in the United States.
Many of those cancers could be prevented with the HPV vaccine. The vaccine Cervarix protects women from both HPV 16 and 18.
“The single dose (of Cervarix) demonstrated equivalent protection to two or three doses,” said Wheeler, a UNM School of Medicine professor and UNM Cancer Center researcher.
“In low-resource countries, giving a single dose of any vaccine is very doable,” Wheeler said. “It’s the logistics of giving two and three doses that creates problems with vaccines that might not be effective.”
The HPV vaccine costs about $120 a dose in the United States. In New Mexico, children 18 and younger can get a free HPV vaccine under the state’s Vaccines for Children program.
The study also found that women who received two doses of Cervarix spaced six months apart were protected against three other types of cancer-causing viruses – HPV 31, 33 and 45 – at rates similar to those who received three doses.
Gardasil, the HPV vaccine most commonly used in the U.S., also is recommended as a three-dose series. The study did not examine Gardasil, but it calls for additional studies with a single dose of Gardasil.
Compliance with multidose vaccines is a problem even in wealthy nations.
In the United States, about 57 percent of adolescent girls had received at least one dose of HPV vaccine in 2013, but compliance with the complete three-dose series was about 38 percent, according to the CDC.
Coverage for a three-dose vaccine has climbed both in New Mexico and the U.S. in recent years. In New Mexico, 44 percent of girls and 38 percent of boys had received a three-dose series in 2013, the state Department of Health reported.
“If one-dose HPV vaccine administration provides strong protection against HPV-16/18 for the long term,” the study concludes, “this approach might be what is necessary to overcome the barriers prohibiting vaccine uptake in many world regions.”