Monkeypox vaccines: what are they, how effective are they and how many are there?

The monkeypox outbreak has resulted in more than 24,000 infections in more than 80 countries, and the World Health Organization (WHO) has warned that the window to contain infection outside of Africa is closing and may become endemic, making vaccines an urgent and potentially crucial measure.

Vaccines are already being deployed around the world, but the struggle continues to secure the limited doses available, while there is concern in poorer nations about access to the biologics.

What vaccines are available for monkeypox?

Three vaccines are being considered for use worldwide to contain the current global outbreak, all of which were developed as smallpox vaccines. However, in the USA, the Food and Drug Administration (FDA) only has one licensed for monkeypox, called MVA-BN, or Jynneos.

Another vaccine is ACAM2000, licensed by the FDA for common smallpox, but can be used for monkeypox with the submission of additional forms. Finally, the third vaccine is LC16m8, which is licensed for smallpox in Japan.

The Jynneos vaccine is considered the safest vaccine, so it will probably be the one of choice on a mass scale. It contains a form of a smallpox-related virus called vaccinia, which cannot replicate in the body, so it seems safe not to make people sick.

Whereas ACAM2000 and LC16m8 contain a form of the vaccinia virus that does replicate in the body, but to some extent. That is, it only causes mild discomfort. However, it is not recommended for people with weak immune systems or who live with people with these conditions.

ACAM2000 is administered through a needle that scratches the surface of the skin and creates a wound that takes weeks to heal. This wound eventually heals and can eliminate the virus, but must be properly cared for. Jynneos, on the other hand, is administered through an injection under the skin, in two doses, and does not crust over.

Both common pox and monkeypox are poxviruses, similar in conformation. Some have been used to protect people against more dangerous viruses of the same family. Both diseases have several commonalities. They are 85% identical. Both can cause a rash with “pustules” on the skin, which eventually crusts over.

The fundamental difference is that monkeypox causes less severe disease. While common smallpox affects only humans, monkeypox can also affect animals, which can become “reservoirs” from which the virus can be passed to humans.

Monkeypox was originally identified in primates, but usually infects rodents.

How effective can monkeypox vaccines be?

The WHO noted that, on the effectiveness of these vaccines, “it was shown through several studies that vaccination against smallpox is about 85% effective in preventing monkeypox,” following research conducted in the 1980s, when scientists investigated an outbreak of monkeypox in what is now the Democratic Republic of Congo.

Other studies report a lower incidence of monkeypox among people immunized against monkeypox, although they are not fully protected. An investigation of an outbreak in the Democratic Republic of Congo in the mid-1990s found that 15% of the 84 people with the disease had been previously vaccinated.