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-- Immunogenicity of the Bivalent HPV Vaccine among Partially Vaccinated Young girls in Uganda

Monday, 28th of January 2013

Abstract Title: Immunogenicity of the bivalent HPV vaccine among partially vaccinated young girls in Uganda

 

Presenter: Mahboobeh Safaeian, PhD

Investigators / Collaborators: Mahboobeh Safaeian, Emmanuel Mugisha, Yuanji Pan, Edward Kumakech, Troy Kemp, Jane Cover, Ligia Pinto, D. Scott LaMontagne

 

Country: United States

 

Objectives

Recent experience with HPV vaccine implementation in Uganda suggests that high vaccine coverage for all three doses could be achieved; however, maintaining a three dose delivery schedule in low resource settings can be challenging. Previous investigations of vaccine efficacy and immunogenicity for female populations receiving less than 3 doses suggest that two doses may be sufficient for protection. Our primary objective was to assess non-inferiority of <3 doses to 3 doses; a second objective was to compare antibody levels of 3 and <3 doses to natural infection levels measured amongst young women participants in the Costa Rica HPV Vaccine Trial (CVT).

 

Method

Young girls who participated in an HPV vaccine demonstration project implemented by the government of Uganda in partnership with PATH (2008-2009) in Nakasongola district in Uganda were eligible for this study. We invited all girls who had received one or two HPV vaccine doses, and selected from those who had received all three doses. We further required at least 24 months post receipt of their last vaccine dose (n1 dose=37; n2 doses=144, n3 doses=195). HPV16 and HPV18 specific antibody levels were measured using an enzyme linked immunoassay (ELISA). We defined non-inferiority as lower bound of the multiplicity-adjusted confidence interval (CI) of the type-specific geometric mean titers (GMT) ratio of greater than 0.5.

 

Results

Ratio of HPV16 and HPV18 GMTs comparing 2 dose to 3 dose groups were 0.51 (97.5%CI=0.37-0.69), and 0.69 (97.5%CI=0.50-0.96).

Due to small sample size, the primary hypothesis for one dose could not be confirmed. In secondary analysis, HPV16 and HPV18 antibody GMTs were higher in all dose groups in our study compared to naturally infected women from CVT (HPV16natural infection=37 vs. HPV161 dose=234, HPV162 doses=812, HPV163 doses=1608; p-value<0.001). Anti-HPV18 GMTs for 1, 2, 3, dose groups were 85, 274, and 396, respectively, compared to 19 among naturally infected (p-value Uganda 1 dose vs. CVT<0.001).

 

Implications and Impact

These data suggest that girls who miss one dose of the 3-dose bivalent HPV vaccine developed a strong immune response that should afford protection against infection despite the lower GMT titers compared to three dose recipients. Programmatic efforts should always focus on delivery of all three doses; however, in challenging environments like Uganda, two doses might be easier and less costly to implement. If this regimen is sufficient to adequately protect vaccinated girls from future infections with vaccine-type HPV, low-resource setting may elect to adopt a two-dose schedule, as has been done in British Columbia, Canada, and is being considered by Mexico and Quebec, Canada.