The first case of mpox occurring in a fully vaccinated individual despite high post-vaccine antibody levels has been recorded in Ireland, new research published in The Lancet Infectious Diseases has revealed.

This unusual case, reported by Dr Joanne Byrne at the Centre for Experimental Pathogen Host Research (CEPHR) in UCD, involved a middle-aged man who presented with a single, small lesion on his nose that tested positive for Monkeypoxvirus Clade IIb. He had received two doses of the Modified Vaccinia Ankara–Bavarian Nordic (MVA-BN) vaccine two years previously.

Mpox (formerly known as monkeypox) is a viral infection that is spread by close person to person contact. In 2022 there was a global outbreak of mpox, which predominantly men who have sex with men.

Vaccination and changes in behaviour led to a significant decrease in mpox cases. However, a further outbreak in Africa of Clade I virus is ongoing, with multiple fatalities, mostly in women and children. Cases of the Clade II also continue to be reported in Ireland in low numbers.

This case is unusual in that it presented with atypical symptoms and also occurred in someone who was vaccinated with high antibody levels. It raises important questions about how best to use mpox vaccines to protect against infection. It also suggests that health care providers need to continue to be vigilant for unusual mpox cases in vaccinated and unvaccinated individuals.

This case is the latest in a number of important findings on Mpox made by UCD CEPHR. In an analysis of more than120 participants within the AIID cohort sampled two years post-vaccination, antibody levels were shown to have reduced substantially, raising questions about the potential need for booster vaccines. The group have also developed a mpox specific antibody test that can measure antibodies that is now being used in clinical trials in Europe and Africa.

The Mpox-Vax study is actively enrolling adults eligible for vaccination at hospitals in Dublin, Galway, and Cork. Mpox-Vax is examining how long vaccine-induced immune responses last and how well vaccine induced immunity prevents infection.

In parallel, through the Mpox-Vax AFRIVAC consortium, funded by the EU, UCD is leading a team of researchers from the Democratic Republic of Congo, Uganda, and Tanzania to study vaccine responses in populations affected by the ongoing Clade I mpox public health emergency of international concern.

This research was supported by funding from the Health Research Board Ireland and the European & Developing Countries Clinical Trials Partnership (EDCTP). Read the full case report published in The Lancet Infectious Diseases.