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Trial supports use of novel IPV during outbreak response
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A novel, monovalent high-dose inactivated vaccine for poliovirus type 2 may be a viable option during an outbreak or for primary protection in areas at risk for the re-emergence of that serotype, according to the results of a randomized controlled trial published in The Lancet Infectious Diseases.
The global switch from trivalent oral poliovirus vaccine (tOPV), which protects against poliovirus types 1, 2 and 3, to the bivalent oral poliovirus vaccine (bOPV), which protects against types 1 and 3, is expected to occur in April. To mitigate risk for poliovirus type 2, the switch has been preceded by the introduction of at least one dose of inactivated poliovirus vaccine (IPV) in routine immunization schedules.
However, researchers said the immune response from standard IPV to poliovirus type 2 is low.
“Achieving better protection against poliovirus type 2 from a single dose of inactivated vaccine could have substantial public health benefit, particularly during the period when tOPV will be replaced by bOPV worldwide, putting type 2 protection at some risk,” they wrote. “With the aim of improving type 2 immunogenicity with a single dose, monovalent high-dose inactivated poliovirus type 2 vaccine (mIPV2HD) was formulated, containing 32 [D-antigen] units of poliovirus type 2, which is four times the content in IPV.”
In an observer-masked, comparative, randomized controlled trial conducted in Panama in 2014, the researchers assigned 233 healthy infants aged 5 to 8 weeks to a single dose of either mIPV2HD or a standard trivalent IPV administered concurrently with a third dose of bOPV at 14 weeks of age.
At 18 weeks of age, infants in both groups were challenged with one dose of monovalent type 2 OPV. Primary endpoints included seroconversion and median antibody titers to type 2 poliovirus 4 weeks after vaccination, and safety.
The researchers recorded seroconversion to poliovirus type 2 in 107 of the 115 infants in the mIPV2HD group (93%; 95% CI, 86.8-96.9) and in 86 of the 115 assigned the standard IPV (74.8%; 95% CI, 65.8-82.4). Median antibody titers against poliovirus type 2 were 181 (95% CI, 72-362) in the mIPV2HD group and 36 (95% CI, 18-113.8) in the IPV group. During the 8 weeks after vaccination, the researchers reported serious adverse events for six infants in the mIPV2HD group and seven in the standard IPV group; none was vaccine-related. No important medical events were reported.
“One dose of mIPV2HD was well-tolerated in infants and induced a superior humoral immune response, both in terms of magnitude as well as kinetics of the response, compared with a single dose of currently available IPV,” the researchers wrote. “On the basis of the promising humoral immunogenicity and safety data from this study, mIPV2HD could be considered an important addition to the options of the polio endgame plan.”
In a related editorial, Roland W. Sutter, MD, MPHTM, of WHO’s polio eradication department, and Olen M. Kew, PhD, of the CDC’s National Center for Infectious Diseases, said the study provides important immunogenicity data for the first use of a novel monovalent polio vaccine.
“Further information about mIPV2HD is being generated in clinical trials in Pakistan, and if they confirm the trial data reported by Sáez-Llorens and colleagues, the Global Polio Eradication Initiative needs to quickly decide whether mIPV2HD should be added to the options for outbreak response, for example, as stockpile vaccine,” Sutter and Kew wrote. “The days of OPV (based on Sabin strains) are limited, because its continued use is not compatible with eradication. IPV, irrespective of seed strains, will remain as the only vaccine for poliomyelitis prevention after removal of bOPV.” – by Jason Laday
Reference:
WHO. The switch from tOPV to bOPV. Implementation guidelines. A handbook for national decision makers, programme managers, logisticians, and consultants 2015. http://www.who.int/immunization/diseases/poliomyelitis/endgame_objective2/oral_polio_vaccine/OPV-Switch-Guidelines-Aug2015.pdf. Accessed January 5, 2016.
Disclosures: Sáez-Llorens and another researcher report personal fees from VaxTrials. Sutter and Kew report no relevant financial disclosures.
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