Atlanta—Vaccination appeared to provide protection against mpox—previously called monkeypox—helping to curb the spread of the sometimes-painful infection.

“Among Jynneos vaccine–eligible men aged 18-49 years in 43 U.S. jurisdictions, mpox incidence among unvaccinated persons was 9.6 times as high as that among persons who had received 2 vaccine doses and 7.4 times as high as that among persons who had received only the first dose,” according to a recent article in the Morbidity & Mortality Weekly Report.

Furthermore, preliminary evidence indicated no difference in protection between SC and intradermal administration routes, CDC authors advised.

The researchers call for further study on the magnitude and durability of protection and continue to recommend that vaccine-eligible persons should complete the two-dose vaccination series.

As of the end of October, more than 28,000 mpox cases had been reported in the United States, with the outbreak primarily affecting gay, bisexual, and other men who have sex with men.

The FDA issued an Emergency Use Authorization for intradermal administration of 0.1 mL per dose, increasing the number of at-risk Americans who could be vaccinated with the available supply of Jynneos. The vaccine was originally approved by the FDA in 2019; the approval was for Jynneos to be administered SC as a two-dose (0.5 mL per dose) series (with doses administered 4 weeks apart for prevention of smallpox and what is now called mpox disease).

A previous comparison of mpox incidence from July 31, 2022, through September 2022, among unvaccinated, but vaccine-eligible, men aged 18 to 49 years and those who had received a Jynneos vaccine dose in 32 U.S. jurisdictions found that incidence among the unvaccinated was 14 times that among those who had been vaccinated (95% CI: 5.0-41.0).

From July 31, 2022, to October 1, 2022, the most recent study period, mpox incidence (cases per 100,000 population at risk) among unvaccinated persons was 7.4 (95% CI: 6.0-9.1) times that among persons who received only one dose of Jynneos 14 days or more earlier and 9.6 (95% CI: 6.9-13.2) times that among persons who received dose 2 at least 14 days earlier.

During that time period, 43 jurisdictions reported 11,581 mpox cases (range across jurisdictions = 2-3,424 cases), with the great majority (82.4%) reported among men aged 18 to 49 years. Among those, 87.2% occurred in unvaccinated people and 12.8% in vaccinated people, including 218 (17.8%) in persons without a known vaccination date.

“Among cases in vaccinated persons whose vaccination date was known, 614 (61%) were in persons whose illness onset occurred ≤13 days after receipt of dose 1 and 392 (39%) in persons with illness onset ≥14 days after receipt of dose 1; among this group, 48 cases (12.2%) (0.5% of all cases) were among persons with illness onset ≥14 days after receipt of dose 2,” the authors pointed out. “Population coverage with ≥1 vaccine dose received ≥14 days before the end of each week increased from 5.7% (July 31) to 45.5% (September 25); 2-dose coverage increased from 0.1% to 17%.”

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