Two-thirds of those vaccinated against smallpox as children may be protected from MPOX

More than two-thirds of those who received the smallpox vaccine as children likely retain some protection against the monkeypox virus type (MPOX) that caused the 2022 outbreak, clade 2. That’s the main finding of a study conducted in Spain, France, the Netherlands and Denmark during that outbreak, and just published in the journal Eurosurveillance.

However, the results suggest that people at highest risk of infection with this MPOX clade 2 virus should be offered a specific vaccine against this virus in accordance with national recommendations, regardless of previous human vaccination against smallpox, until more data are available to inform future vaccination strategies. In 1980, the World Health Organization (WHO) declared smallpox eradicated. In fact, it was the first human disease to disappear from the planet, although Russia and the United States kept samples of the virus in high-security laboratories. Thanks to vaccination campaigns – one of the first, the historic Balmis expedition (1803-1806) with the Galician nurse Isabel Zendal, who brought immunization to the Americas – the eradication of the virus achieved over centuries killed hundreds of millions of people. Its disappearance was also facilitated by the fact that smallpox infected only humans, so it had no animal reservoirs.

The monkeypox virus belongs to the same genus of viruses, Orthopoxvirus, as the one that causes smallpox. That’s why virologists knew that the “historical” smallpox vaccine might provide some protection against monkeypox. The last case of natural smallpox infection was diagnosed in Somalia in 1977, and vaccination against the virus was stopped in Spain in 1979.

The researchers in the European study, including scientists from the Carlos III Institute of Health in Madrid, found that in a European context, more than two-thirds of men vaccinated against smallpox as children are likely to retain some protection against MPOX caused by monkeypox virus clade 2. However, in their paper, the scientists add that “the degree of protection varied greatly across the four countries they studied,” likely due to differences in smallpox vaccination schedules, so “further studies are needed to more firmly confirm these results.”

The authors recall that studies conducted in the Democratic Republic of Congo more than 30 years ago showed that a smallpox vaccine based on the cowpox virus was more than 80% effective in preventing monkeypox and reducing the severity of the disease caused by the clade 1 virus.

WHO Director-General Tedros Adhanom Ghebreyesus has assured that the current MPOX outbreak is “controllable and stopable”, announcing a plan that will cost around €120 million over the next six months. “Let me be clear: this new MPOX outbreak is controllable and stopable (…) “This requires a comprehensive and coordinated international response,” he said during an information session for Member States, which he called on to work in collaboration with international organizations, civil society, researchers and manufacturers.

Almost 21,500 cases and 591 deaths from monkeypox have been reported in 13 African countries since January 1, the African Union (AU) health agency said last Friday.