THE ARISING · Science & Frontiers
BioNTech's mRNA Mpox Vaccine Produced Phase-1 Antibody Responses, With Waning Neutralization
A 64-person phase-1 study reported antibody responses and adverse events after BNT166a. Binding responses persisted, but neutralizing antibody levels declined toward baseline; protection against mpox was not tested.
The mRNA platform that delivered COVID-19 vaccines in record time is now aimed at mpox. BioNTech's candidate, BNT166a, has produced its first-in- human results, including antibody responses and adverse events in a small uncontrolled study. The open question is durability.
Our research desk described an experimental mpox vaccine reaching human testing. It reported 48 volunteers with no prior smallpox or mpox vaccination and 16 who had received the old smallpox vaccine. It noted local reactions after the first dose in 50, 81 and 88 percent of unvaccinated participants across rising doses.
The desk said its source did not provide the antibody results. That turned out to be incomplete. The published paper reports them in detail.
We confirmed the study in The Lancet Infectious Diseases (volume 26, issue 10). Frank Bähner of BioNTech led it, with academic sites in the UK and US.
The vaccine encodes four mpox virus proteins. Participants were screened between September 2023 and March 2024, so this is a published readout from part of the ongoing BNT166-01 trial, which has three sub-studies, not a trial just starting. It was open-label, with no placebo group.
The 48 unvaccinated adults received two shots four weeks apart at one of three doses. The 16 previously vaccinated adults were also part of the study.
SAFETY
Our desk's reaction figures match the paper. Reactions were more common after the second dose. Most were mild to moderate. At the top dose, two people had severe systemic events after dose two, including one grade 4 fever. One case of severe neutropenia was judged vaccine-related. Three serious adverse events were judged unrelated.
ANTIBODIES
Every participant who got both doses made binding antibodies against all four targets two weeks after the second shot, and those persisted to 12 months. Neutralizing antibodies against clade IIb mpox appeared in 62, 71 and 92 percent of unvaccinated people as dose rose.
The abstract also reports neutralizing responses against vaccinia. Neutralizing levels peaked two weeks after dose two in vaccine-naive participants and at one month in previously vaccinated participants, then declined toward baseline over the year. The authors concluded the profile supported moving to phase 2.
Mpox outbreaks in 2022 and since showed how quickly an old virus can spread in new ways. The current licensed vaccine relies on a weakened live virus that is slower to manufacture at scale. An mRNA option could be produced faster when outbreaks flare.
• If you are at higher risk of mpox exposure, ask your doctor about the currently licensed vaccine; BNT166a is not available outside trials.
• Do not assume childhood smallpox vaccination still protects you; immunity wanes. • International travelers to outbreak regions should check current public-health advisories before departure.
• "Reaches human testing" is dated framing. Screening occurred in 2023–24; this is a published readout, not a newly starting trial. • No efficacy data. Antibody levels are a surrogate. Nobody yet knows whether BNT166a prevents infection or severe disease in people. • Waning neutralization. Neutralizing responses fell back toward baseline within a year, which raises a question for further study about durability and any need for boosters. • Small and uncontrolled. Sixty-four people with no placebo group cannot detect rare side effects.
• Phase 2 results, including larger safety numbers and booster strategies. • Any efficacy study during an outbreak, or animal-to-human bridging data accepted by regulators. • How BNT166a compares with the existing licensed vaccine head to head.