Smallpox Vaccination May Protect People Against Mpox Clade 2

Eurosurveillance (Volume 29, Issue 34) published an article today reviewing the immunization benefits from previous smallpox vaccinations.

On August 22, 2024, these researchers wrote that following the eradication of smallpox 40 years ago, routine smallpox vaccination ended, leading to a growing proportion of the European population being susceptible to other Orthopoxviruses, such as monkeypox virus (MPXV).

With the recent surge in mpox cases globally, we sought to determine the effectiveness of historical smallpox vaccination, such as ACAM2000®, against mpox caused by MPXV clade II to inform ongoing vaccination policies.

Our analyses revealed that in a European setting, about 70% of men in Denmark, France, the Netherlands, and Spain vaccinated against smallpox during childhood are likely to retain some protection against mpox caused by MPXV clade II.

However, the degree of protection varied widely among the four countries we investigated, likely due to the differences in smallpox vaccination schedules.

Our findings suggest that individuals at higher risk of MPXV clade II infection should be offered mpox vaccination, which aligns with national recommendations, regardless of prior smallpox vaccine history, until further evidence becomes available to inform future mpox vaccination strategies.

To our knowledge, this study is the first to assess the effectiveness of smallpox vaccination against mpox regardless of severity in Europe.

Another study, published on August 16, 2024, found that the protection data showed that smallpox vaccination effectively reduced the risk of severe monkeypox infection (RR: 0.61; 95% CI: 0.42–0.87).

Furthermore, third-generation vaccines, such as JYNNEOS® (MVA-BN®, IMVAMUNE®), showed greater efficacy (RR: 0.36, 95% CI: 0.22–0.56) than first-generation vaccines. 

Recently, U.S.-based Emergent BioSolutions supported the current mpox clade 1b outbreak across Central Africa by donating 50,000 doses of its second-generation ACAM2000 vaccine.

Of note, military service has generally required smallpox vaccination in most countries, suggesting those people may have some degree of mpox protection. In September 2023, the NEJM published a Correspondence that concluded that ACAM2000 vaccination prevented Mpox in military personnel.