traditional technology, for what protection?

Designed against a related disease, the monkeypox vaccine is used to protect those most at risk from the disease spreading outside of endemic areas. Update on its operation and effectiveness.

– What vaccine?

It is a vaccine against human smallpox, a fatal disease eradicated in 1980, which is currently used against monkeypox.

These two viruses are part of the “orthopoxvirus” family. The serum uses a third virus of this family, genetically close, that of the vaccinia.

The vaccine, harmless in humans, enabled the British doctor Edward Jenner in the 18th century to develop the very principle of vaccination (and to create the first anti-smallpox vaccine): to educate the immune system by confronting the organism with a virus close to the one to be fought.

“There is 90-95% homology of the viral proteins involved between the smallpox and monkeypox viruses. So taking a very close vaccine to block it is a proven strategy,” says Olivier Schwartz , head of the virus and immunity unit at the Institut Pasteur.

The current vaccine, made on cell culture and no longer on animals, is said to be “third generation because it has been improved compared to the two previous ones to limit side effects”, specifies Yannick Simonin, lecturer at the University of Montpellier. , specialist in emerging viruses.

– What protection?

Smallpox infection confers cross-protection against the cousin monkeypox virus, a similar mechanism with the smallpox vaccine against monkeypox.

Although there are not yet large-scale data, past epidemiological elements and laboratory tests suggest that the current anti-smallpox vaccine will be highly effective against monkeypox.

“The vaccine protection figure of 85% dates from studies in the 1980s and 1990s in the field in Zaire and is quite approximate”, notes Olivier Schwartz.

He also mentions studies in caregivers in 2018 and experiments on macaques that seem to show a strong effectiveness of post-exposure vaccination to monkeypox.

Having been vaccinated against smallpox before 1980 provides a priori immune protection against monkeypox, of an uncertain extent and duration.

“According to studies, for example from the 2000s, antibodies against smallpox were found in 30% of people vaccinated at least 20 years earlier,” says the Pasteur researcher. And “a booster dose will activate memory cells – B or T lymphocytes – and reactivate cellular immunity, even after 20 or 40 years”.

Yannick Simonin warns, however, that immunity “decreases over time and that the persistence of neutralizing antibodies against monkeypox has never been evaluated”.

– What output?

The only vaccine currently authorized for monkeypox is manufactured by the Danish Bavarian Nordic, from the viral strain MVA-BN (modified vaccinia Ankara virus).

It is marketed as Jynneos in North America, Imvanex in Europe.

Several countries and the WHO keep stocks of smallpox vaccine for security, particularly in the face of a bioterrorism risk. Bavarian Nordic partnered with US authorities in 2003, and has already delivered 30 million doses to them. Since the current outbreak of monkeypox, an agreement provides for 7 million additional doses.

According to the WHO, there are currently 16 million doses of MVA-BN in the world, mostly in bulk, which would require a few months before being bottled to use them. It is difficult to know the state of the stocks, the countries opposing defense secrecy to the chagrin of associations and elected officials.

We also do not know the details of the orders from the only current manufacturer. The EU has so far ordered 100,000 doses.

Bavarian Nordic has an annual production capacity of 30 million doses. Two other smallpox vaccines, LC16 and ACAM2000, produced by other laboratories, are under study. Emergent BioSolutions, the American laboratory that produces ACAM2000, told AFP that it has an annual production capacity of 18 million doses, which could reach 40 million doses per year if necessary.

– What distribution?

Despite the presence on part of the continent of areas endemic for monkeypox, more than 3,000 confirmed cases and, according to doctors, more than 70 potential deaths, Africa still has no dose of vaccine.

The WHO has asked countries with vaccines to “share them with countries that do not have them”, calling not to reproduce the Covid-19 scenario, when rich countries have kept almost all of the vaccines for many months. vaccines available.

“Is there a risk that the countries submitting (requests) for access are rich countries? It is quite possible,” Meg Doherty, director of WHO’s HIV programs, said on Sunday. hepatitis, sexually transmitted infections, calling for ‘fairness’ on monkeypox at an International AIDS Conference.


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