Vaccination with the Jynneos smallpox vaccine was found to offer strong protection against mpox infection after one or two doses, according to a study conducted by the Centers for Disease Control and Prevention (CDC), providing some of the first clinical evidence on the efficacy of the shot used to fight back against the mpox outbreak this year.
New data released in the CDC’s Morbidity and Mortality Weekly Report found that the incidence of mpox infections among unvaccinated people was nearly 10 times higher when compared to the incidence rate among fully vaccinated individuals, and 7.4 times higher when compared to those who had received only one dose.
This data was specific to vaccine-eligible men between the ages of 18 and 49, who accounted for the bulk of mpox cases in the U.S.
The CDC acknowledged that more data was still needed to fully determine the impact of Jynneos against mpox, which was formerly known as monkeypox, but stated that this study indicated the drug’s efficacy.
The worst of the mpox outbreak, which surged among communities of gay and bisexual men this year, appears to have passed. The seven-day moving average now stands at six cases per day according to the most recent federal data.
This outcome has been largely attributed to quick changes in behavior among gay and bisexual men, many of whom reported taking more precautions in response to the outbreak, such as reducing their number of sexual partners and encounters.
There are currently no vaccines or treatments specifically designed to treat mpox. With the onset of the outbreak among nonendemic countries this year, health officials turned to using treatments for smallpox, as it falls within the same family of viruses that mpox belongs to. This included the vaccines Jynneos and ACAM2000, as well as the antiviral treatment TPOXX.
The vaccine campaign had a rocky start, with thousands of eligible individuals unable to access the shots and many left only partially vaccinated due to the uncertainty over when more doses would be available.
In order to stretch the supply of Jynneos vaccines, the federal government implemented a strategy of administering one-fifth doses of the drug intradermally, appearing to base this decision on a 2015 study specifically looking into this form of administration.
The CDC noted in its weekly report that the analysis of cases did not suggest a difference in protection between intradermal shots and subcutaneous ones, which are administered into the muscle and include a full dose of the vaccine like most other immunization injections.
Citing the low number of mpox cases currently being reported, the Department of Health and Human Services (HHS) announced last week that it does not expect to renew the public health emergency for the mpox outbreak when it expires at the end of January.
“Over the next 60 days we will focus on supporting jurisdictions and the Department to ensure the expiration of the PHE will not hinder response efforts,” HHS said. ““Mpox continues to be a priority for HHS and the Administration more broadly, and we do not expect the expiration of the PHE to impact the Administration’s ability to get vaccinations, tests, and treatments to affected individuals.”