Why some smallpox vaccines are also effective against monkeypox

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📌Smallpox (smallpox) and monkeypox (monkeypox) are two diseases caused by viruses that are very similar to each other.
📌 Both have a similar clinical picture, although less serious in the monkey, according to the WHO: fever, malaise, headache, intense fatigue, intense back pain and the appearance of spots on the skin that turn into small blisters. .
📌 The FDA approved in September 2019 the Jynneos vaccine (in Canada it is called Invamune and in Europe, Imvanex), the only one so far approved to prevent human and monkey smallpox in the United States. The ACAM2000 vaccine is also approved, which is used to prevent human smallpox, but is also used to prevent monkeypox, although that is not its “target” disease:

Smallpox (in English, smallpox) It was a disease declared eradicated on the 1980 World Health Assembly.

Much of the success of this global effort was due to vaccines and campaigns to administer them to the entire population.

Now, new cases of monkey pox (in English, monkeypox), a disease considered endemic in central and western Africa, but which is reporting outbreaks in countries outside this area such as United States, Canada and Mexico.

Could the eradicated smallpox vaccine be effective against another type of smallpox? The evidence says yes. albeit with nuances. We tell you.

Human and monkey pox are very similar viruses.

To understand why a vaccine works on a different virus, the first thing to understand is that the smallpox and the monkeypox They are two diseases caused by viruses that are very similar to each other.

Both are viruses that belong to the gender of Orthopoxvirusa classification of pathogens that can infect both animals and humans, such as the CDC explains (Centers for Disease Control and Prevention).

In addition to human and monkey pox, other Orthopoxvirus known are the cowpox or the virus Vacciniawhich was used in the vaccine against smallpox.

Human and monkey pox have a similar clinical picture, although less severe in the second, according to the World Health Organization (WHO)): fever, malaise, headache, severe fatigue, severe back pain, and patches of skin that develop into small blisters.

In addition, the Orthopoxvirus they are not easily dispersed through the air – although they can be present in droplets expelled by coughing or sneezing – and require prolonged direct contact with the source of the pathogen, be it an animal, a person with the disease or a contaminated object , details the Professor of Cellular Biology Guillermo López Lluch in The Conversation and the gate of Mayo Clinic health information.

With all this, there a vaccine licensed in the United States one that is approved to prevent infection with monkeypox and smallpox, and another that is approved only for smallpox but has also been shown to be effective in preventing monkeypox.

Vaccines in the United States that would serve against monkeypox

The FDA (United States Food and Drug Administration) approved in September 2019 the vaccine Jynneos (in Canada it is called Invamune and in Europe, Imvanex), the only one so far approved to prevent human and monkeypox in this country.

This drug uses a modified form of the virus Vaccinia ‘surnamed’ Ankara that it does not replicate in the human body and that it is not capable of generating a disease.

This vaccine stimulates the creation of antibodies that are capable of identifying other Orthopoxvirusas the smallpox and the monkeypox.

The CDC details that this vaccine can be used in people 18 years of age or older who are at high risk of infection with monkeypox or humanpoxsuch as laboratory personnel who investigate with Orthopoxvirusemergency or health personnel who deal with patients infected with this type of virus.

Exists another FDA-approved vaccine to prevent smallpoxbut which is also used for the prevention of monkeypox, although that is not its “target” disease: the ACAM2000.

This vaccine is made with a virus Vaccinia vivo capable of replicating -without the modifications of the Jynneos vaccine- which causes a much milder disease than smallpox.

In addition, it has a different administration than the traditional puncture of a vaccine: it requires the skin to be punctured several times with a double-pronged needle.

The AICP (Advisory Committee on Immunization Practices, which is part of the CDC), recommended in 2015 to use the ACAM2000 vaccine in people who are at risk of getting infected with Orthopoxvirus.

In November 2021, the AICP added the Jynneos vaccine to this recommendation..

Original (first generation) vaccines are not recommended

Vaccines used by countries during the intensive part of smallpox vaccination campaigns, which ran until 1980, are considered first generation vaccines.

They are the original drugs and are kept in strategic reserves of the WHO and some countries, as explained by the international health organization in its document Vaccines and immunization for monkeypoxpublished in June 2022.

In this document, the WHO highlights that these vaccines “are not recommended for monkeypox at the moment”, since “they do not meet current safety and manufacturing standards.

However, there is evidence that these vaccines do have some effectiveness (up to 85%) in preventing monkeypox, based on the fact that certain populations in Africa who received this drug and who showed protection against monkeypox.

Instead, the WHO indicates that second and third generation vaccines used for human smallpox could also be used for monkeypox.

those of second generationexplains the report, “use the same strains of the virus Vaccinia (or cloned copies) that were used in the first generation of vaccines, purified and manufactured in cell lines. An example of a second generation vaccine is ACAM2000.

Lastly, those of third generation they refer to vaccines with “more attenuated” strains developed as “safer vaccines” and with little or no ability to replicate in humans.

Two examples of this vaccine is the Jynneos or the LC16, approved in Japan to prevent smallpox.


This is an article in alliance with fact checkeda means of verification that builds a Spanish-speaking community to counter disinformation in Spanish in the United States.

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