猴痘MVA-BN疫苗皮内给药部分剂量在疫苗供应紧张的疫情反应中的常见问题（FAQ）

19June2025 This document outlines keyconsiderations for the use offractional dosingwith intradermaladministrationof the MVA-BNmpoxvaccine in response to ongoing mpox outbreaks. In light ofthe limited availability of vaccineandcurrentWHO recommendations, national authoritiesmay, as a temporaryoutbreak responsemeasure, consider administering MVA-BNvaccineviaintradermal injection at a reduced dose to protect individuals at risk of exposure. 1.What are theWHO recommendationsonmpoxMVA-BNvaccineintradermalfractionaldosing? WHO has previouslyrecommendedthe “off-label”1useof a singlefulldoseof MVA-BNvaccine(0.5mL/dose)administeredsubcutaneously or fractionaldosing(0.1mL/dose)administeredintradermallyin supply-constrained outbreak situations2.In thisdocument,WHOfurtherprovidesguidance ontheoff-labeluse ofasingleor two-dosefractionalregimen.Thisapproachis intended to maximize the number of individuals who can be vaccinated usingthe availablevaccine supply. At the same time,WHO emphasizes the need to collect further data on vaccine safety,effectiveness,and duration of protectionin thesecircumstances. 2.Whatis anintradermalfractional doseof mpox MVA-BN vaccine? Onefull dose of MVA-BN vaccine is0.5 mLsuspensionprovidedin asingle-dosevial. A fractionaldose (0.1 mL) is a reduced dose of the same vaccine, equivalent to one-fifth of theusualdose(each single-dose vial provides 4-5 fractional doses).As the volume of the given dose is smaller,a fractional dose will be administered intradermally (given just below the top layer of the skin) usinga 0.1 mLauto disable(AD)syringewith a shorter needle (10-13 mm). A summary of MVA-BNvaccinecharacteristics is provided inTable1. 3.Is itsafeto administer a fractional dose of mpox MVA-BN vaccineintradermally? Yes,however,self-resolvingnon-severe side effects are more common following intradermalthan subcutaneous administration. A study conducted in the UnitedStates of Americareported that although the intradermalvaccination site displayed erythema/induration (>30 mm),this mode of administrationdid nothamper the ability of the person vaccinatedto perform routine activities.3 A studypublished in 2023analyzing data from Australia’s vaccine safety surveillance systemexamined adverse events following subcutaneous andintradermal administration of MVA-BN.Adverse events were highest after the first dose of intradermal vaccination (53%) and lowest afterthe second dose of subcutaneous vaccination (31%). The most common reported reactionsincluded local redness, itching,and swelling for intradermal vaccination, and local pain, swelling,and redness for subcutaneous vaccination4. Another studypublished in 2024reported thefrequency ofsystemic and local side effects followingintradermal and subcutaneous administration of MVA-BNvaccinein Italy. Systemic adverse events were more frequently observed after intradermal vaccination compared to subcutaneous (59%versus46%), as were local adverse events (94% versus80%)5. Finally, an analysis of the Bavarian Nordicglobal safety databasepublished in 2024, reported thatfainting episodeswere more common withintradermal administration6. 4.Isintradermalfractional doseasimmunogenic andeffectiveas asubcutaneousfull dose? Yes. Regarding immunogenicity, aclinical trial published in 2015 involving approximately 500 adultscompared intradermal fractional dosing with subcutaneous administration of the MVA-BN vaccineas two-dose schedules with a 28-day interval between doses. The study concluded that individualsreceiving the vaccine intradermally produced similar levels of antibodies as those who received thefull subcutaneous dose7.Similarly, other studies found no significant difference in neutralizingantibody titers between subcutaneous and intradermal administration8,9.One study even reportedthat intradermal administration resulted in higher neutralizing antibody levels one month after MVA-BN vaccination compared with subcutaneous administration10. With respect to vaccine effectiveness (VE),a case-control study conducted in theUnited Statesreported that VE did not significantly differ between subcutaneous and intradermal routes ofadministration. These VE estimates pertain to the global outbreak associated with the Clade IIbMPXV genetic lineage. Notably, the published VE data are based on studies conducted among gay,bisexual, and other men who have sex with men (MSM), aged 18–49 years, in North America andEurope, with a relatively short follow-up period after vaccination11. These results support the use of intradermal fractional dosing. 5.How manyintradermalfractionaldosesare recommended? Available data on intradermal administration of theMVA-BN vaccine are based on one or twofractional doses. A case-control study conducted in the United States showed that a single dose ortwo doses, whether administered subcutaneously or intradermally, provided similar vaccineeffectiveness13. Countries may consider the off-label use of one or two intradermal fractionaldose