NEW YORK (Reuters Health) – A challenge to broadly implementing human papillomavirus (HPV) vaccination programs in developing countries is delivering all 3 recommended doses of vaccine to adolescents within 6 months.
A new study shows that it’s possible to adopt a more flexible dosing schedule, giving the 3 shots over a longer period of time, and still achieve antibody concentration levels that are comparable to the standard vaccine schedule.
Dr. Kathleen M. Neuzil, of the nonprofit group PATH in Seattle, Washington, and colleagues report their findings in the April 13 issue of JAMA, a theme issue on infectious disease and immunology.
“As with most vaccines, initial testing for licensure is done according to strict schedule guidelines,” Dr. Neuzil told Reuters Health. “Our study adds to a growing body of evidence that girls who receive 3 doses of HPV vaccine within a year, even if there are long delays between doses, have strong immune (antibody) responses,” she noted.
“This should be reassuring to physicians when girls present late for their second or third dose of vaccine. These data may also contribute to country-specific policy decisions on more flexible or alternative scheduling,” Dr. Neuzil said.
The study team tested the immunogenicity and reactogenicity of 4 alternative schedules of quadrivalent HPV vaccine in an open-label, cluster randomized, noninferiority trial in northwestern Vietnam. Twenty-one schools and 903 adolescent girls between 11 and 13 years old at enrollment participated.
Intramuscular injection of 3 doses of quadrivalent HPV vaccine was delivered on a standard dosing schedule (at 0, 2, and 6 months) or 1 of 3 alternative dosing schedules: 0, 3, and 9 months; 0, 6, and 12 months; or 0, 12, and 24 months). Of the 903 girls, 809 (89.6%) received all 3 doses of vaccine and had a serum sample available for testing after the final dose of the HPV vaccine.
For all 4 vaccination schedule groups and vaccine types, the anti-HPV antibody concentrations were low at the beginning of the study and increased significantly after receipt of 3 doses of the vaccine.
Compared with standard dosing, the alternative dosing schedule of 0, 3, and 9 months and 0, 6, and 12 months met noninferiority criteria (as determined by the level of antibody concentrations) for the anti-HPV-16 and anti-HPV-18 responses at 1 month after receipt of the third dose.
Compared with standard dosing, the alternative schedule of 0, 12, and 24 months met noninferiority criteria for HPV-18 but not for HPV-16.
The alternative dosing schedules were well tolerated and the safety profiles were comparable with the standard dosing schedule, the study team notes.
They also note that the results are consistent with those of a study conducted last year among college-aged women in the United States. In this study, the HPV vaccine given on a 0, 2, and 12 month schedule yielded comparable immune responses to that of the standard schedule.
“The similarity of the immunogenicity and reactogenicity profiles of the HPV vaccine reported from this predominantly ethnic minority population in a low-resource area of Vietnam and other populations throughout the world is reassuring and supports more widespread introduction of the vaccine,” Dr. Neuzil and colleagues conclude.
“The option of delivering HPV vaccine on flexible schedules will allow countries to minimize costs and maximize feasibility according to local vaccination practices,” they add.