Can the vaccine be relied upon to prevent a monkeypox pandemic?

• In Europe as in the United States, cases of monkey pox are increasing all over the world.

• Several countries confronted with the virus have thus decided to set up a vaccination strategy.

• In France, the High Authority for Health recommends this Tuesday to vaccinate the contacts of confirmed cases.

United Kingdom, Spain, United States, France, but also Portugal, Sweden, Morocco and the Czech Republic: in recent days, cases of simian orthopoxvirus, better known as monkey pox or Monkeypox, have multiplied at across the globe, raising the specter of a new pandemic succeeding that of Covid-19.

Although the number of cases, contagiousness and severity of these two viruses differ greatly, health authorities in several countries are considering the best strategy to stem the spread of this monkeypox.

A strategy that relies on the administration of the classic smallpox vaccine.

In an opinion published on Tuesday, the High Authority for Health (HAS) thus recommends the vaccination of contact cases.

So, will the vaccine save us from another pandemic?

People over 50 immunized with the classic smallpox vaccine

To date, “there are no specific treatments or vaccines against monkeypox, but outbreaks can be contained, explains the WHO.

Smallpox vaccination has been proven in the past to be 85% effective in preventing monkeypox.

Because “Monkeypox is not the human smallpox virus, they are two close but different viruses, indicates to

Dr. Jean-Daniel Lelièvre, head of the immunology and infectious diseases department at Henri-Mondor hospital.

The protection conferred by the smallpox vaccine against Monkeypox is therefore logically not total, but it offers cross-protection here, protecting moreover more against the disease than against infection, as can be seen with Sars-CoV2 ".

Thus, today, “we can estimate that older people will be protected against monkeypox, in particular those over 50, continues Dr. Lelièvre.

Those born in the 1960s and 1970s, because this is the last generation born at the time of compulsory smallpox vaccination.

With the problem that as we age, we lose immune populations, so we cannot speak here of collective immunity.

However, the oldest do not seem to be among the groups at risk of contact with this infection.

Vaccination of contact cases recommended in France

With at least three cases of monkey pox confirmed in France, others should probably be identified over the next few days in France, prompting the health authorities to think about the best response to adopt in the face of this situation.

And to bring out this good old vaccine from the drawers.

Thus, in an opinion published on Tuesday, the HAS validates “the principle of a post-exposure reactive vaccine strategy with the third-generation smallpox vaccine”.

Clearly, the HAS recommends the vaccination of contact cases as soon as possible after exposure to the virus.

"As soon as a case of infection is identified following an investigation by the ARS and the regional public health unit France", the vaccine should be "administered ideally within 4 days after the contact at risk and a maximum of 14 days later with a two-dose regimen (or three doses in immunocompromised subjects), spaced 28 days apart”, explains the HAS.

This concerns “adult contact persons at risk of exposure to Monkeypox, including health professionals exposed without personal protective measures”.

A strategy already applied

A strategy that is not new.

“Vaccination of contact cases has already been developed and adopted in the past in the context of smallpox, then in a second phase to fight against the spread of the Ebola virus.

Moreover, the first Ebola vaccine to have received marketing authorization is a vaccine whose effectiveness is based on a clinical trial based on the technique of vaccination of contact cases, or ring vaccination”.

The principle, for optimal efficiency, “is to vaccinate the contacts of the contacts, explains Dr. Lelièvre.

Because there is always a certain inertia in the effectiveness of a vaccine: we have seen this with the anti-covid vaccine, which is effective from the fourteenth day after the injection.

Before, immunity does not have time to establish itself.

As we know that people who have been in direct contact with the infected person may already be in the incubation phase, there is still an interest in vaccinating them, but it is interesting to vaccinate their own contacts, for the prevent them from transmitting the virus around them in turn, and thus break the chains of contamination.

This type of vaccination is relevant when the disease has spread little, as is the case today with monkeypox,

which is much less contagious than the coronavirus, with a very low R0 [reproduction rate].

In the case of Covid-19, the virus was already so widespread in the population that we went directly to the stage of wide vaccination in the general population”.

World production of smallpox vaccines halted

A large vaccination against smallpox has not been relevant for decades.

“The total eradication of smallpox was officially declared by the WHO at the 33rd World Health Assembly in 1980, recalled in 2006 the Ministry of Health in its updated national plan to respond to a smallpox threat.

In France, vaccination against smallpox was compulsory until 1979. On that date, it was decided to no longer impose primary vaccination against smallpox before, finally to completely abolish the vaccination obligation in 1984, i.e. long after the occurrence of the last case of smallpox in the world (1977 in Somalia) and while all the countries adhering to the WHO also decided to stop systematically vaccinating against this disease”.

Result: “The vaccine is no longer available to the general public after its manufacture was stopped following the global eradication of smallpox,” notes the WHO.

So how to apply this strategy of vaccination of contact cases if the vaccine is no longer produced?

Does France have sufficient stock?

Impossible to give a precise number.

“Stockpiles of vaccines against smallpox almost fall within the domain of national defense because today it is a potentially bioterrorist agent,” specifies Dr. Lelièvre.

However, it is not a new pathogen, we know how to manufacture these vaccines, and if necessary, large-scale manufacturing could be restarted, unlike Covid-19 ”.

So don't panic, reassures Dr. Lelièvre, "we have the necessary doses to ensure ring vaccination".

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