LJUBLJANA, SLOVENIA – Vladimir Gilca, MD, PhD, reported at the annual meeting of the European Society for Paediatric Infectious Diseases.
This novel observation from a post hoc analysis of two clinical trials conducted by the same research team has important potential implications for both clinical practice and public health, according to Dr. Gilca of the Quebec National Institute of Public Health and Laval University, Quebec City.
“A less rigid immunization schedule might facilitate the coadministration of HPV vaccine with other vaccines, such as meningococcal or Tdap, and reduce the number of vaccination visits. Also, our data support the decision to offer only one dose in cases of vaccine shortage, like we have presently in many countries around the world, with the possibility of giving the second dose several years later when the shortage is resolved,” he said.
He presented a comparison of anti-HPV geometric mean IgG antibody titers and their distribution in two clinical trials with serologic assays performed in the same lab using the same enzyme-linked immunosorbent assay procedures. In the first study, 173 boys and girls aged 9-10 years received two doses of a 9-valent HPV vaccine 6 months apart. In the second trial, 31 girls were vaccinated with one dose of a quadrivalent HPV vaccine at age 9-14 years and then received a dose of the 9-valent vaccine at a mean of 5.4 years and maximum of 8 years later. Blood samples were obtained before and 1 month after the second dose in both trials.
Despite the enormous differences in the time between the first and second doses in the two studies, 100% of subjects in both trials were seropositive to HPV 6, 11, 16, and 18, with similar geometric mean titers and titer distributions before dose number two. Moreover, 1 month after the second dose, the geometric mean titers jumped 40-91 times in study participants with a 6-month dosing interval, and similarly by 60-82 times in those with the far lengthier interval. Titer distributions after the second dose were equivalent in the two studies.
Dr. Gilca and coinvestigators looked at subgroups who received their second dose 3-4 years, 6, or 7-8 years after the first. The time difference didn’t affect the distribution of antibodies.
“We conclude that delayed administration of the second dose has no negative impact on the magnitude of the immune response,” he declared.
There are abundant precedents for this phenomenon of high immunogenicity of delayed doses of vaccine. Rabies, anthrax, hepatitis A and B, and tick-borne encephalitis vaccines have all been shown to elicit at least a similar magnitude of immune response after delayed administration of a second or third dose, compared with dosing at the guideline-recommended intervals, he noted.
Asked about the possible approach of giving just one dose of HPV vaccine, as was supported based upon retrospective data in a high-profile presentation earlier at ESPID 2019, Dr. Gilca replied, “The data we’ve seen so far show clinical noninferiority between one, two, and three doses. An approach that might be used by at least some countries is to give, for example, one dose of HPV vaccine in grade 4 and to then wait for confirmatory data about the efficacy of one dose, which we expect in the next 4-5 years. At least five or six clinical trials are ongoing on one dose versus two or three doses.”
He reported having no financial conflicts of interest regarding his presentation.
SOURCE: Gilca V et al. ESPID 2019, .