In contrast to a recent Dutch preprint that cast doubt on the efficacy of Bavarian Nordic's Jynneos (modified vaccinia Ankara [MVA]) vaccine to produce significant neutralizing antibodies to monkeypox, the company has released its own preprint study showing that single and two-dose Jynneos vaccinations administered subcutaneously induced durable neutralizing antibody responses in healthy volunteers.

Results were comparable to older-generation replicating smallpox vaccines.

The study included healthy adult volunteers who had never been vaccinated against smallpox and were randomized to receive either placebo injections or one or two doses of MVA. The one-and two-dose MVA produced strong antibody responses at week 2 after injection and further increased at week 4.

High neutralizing antibodies compared to baseline were observed for at least 6 months in all groups, with a return to baseline at year 2, the authors said.

No serious adverse events were recorded, though most participants reported some injection site redness or pain.

The authors also studied a single booster dose of MVA in volunteers who had previously been immunized against smallpox.

"A single MVA-BN booster administered to those initially vaccinated with older generation replicating smallpox vaccines in the distant past also evoked a rapid increase in neutralizing antibody titers, that was highest at 2 weeks and remained elevated relative to baseline at 6 months after vaccination," the authors wrote.

"These data suggest that priming with 1 or 2 doses of MVA-BN can induce B-cell immune memory similarly to that of older generation replicating smallpox vaccines, which have conferred long-term protection and are believed have prevented orthopox outbreaks (including Monkeypox transmission) until recently."

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