The monkeypox vaccine, developed against a related disease, is used to protect those most at risk from spreading the disease outside endemic areas. Update on its operation and effectiveness.
– What vaccine?
It is a vaccine against human smallpox, a deadly disease eradicated in 1980, which is currently used against monkeypox.
These two viruses are part of the “orthopoxvirus” family. The serum uses the third virus of this family, genetically close, vaccinia virus.
A vaccine that is harmless to humans allowed the British doctor Edward Jenner in the 18th century to develop the very principle of vaccination (and create the first smallpox vaccine): to educate the immune system by confronting the body with a virus close to the one that needs to be fought.
“There is 90-95% homology in the viral proteins used between smallpox and monkeypox viruses. So using a very close vaccine to block it is a proven strategy,” says Olivier Schwartz, head of viruses and immunity at the Pasteur Institute. .
The current vaccine, created in cell culture rather than animals, is considered “third generation because it has been improved over the previous two to reduce side effects,” said Yannick Simonin, a lecturer at the University of Montpellier. emerging virus specialist.
– What protection?
Smallpox infection provides cross-protection against the related monkeypox virus, a similar mechanism with the monkeypox vaccine.
Although large-scale data are not yet available, past epidemiological data and laboratory testing suggest that the current smallpox vaccine will be highly effective against monkeypox.
“The 85% vaccine protection figure is based on studies done in the 1980s and 1990s in Zaire and is quite an approximation,” notes Olivier Schwartz.
He also cites a 2018 study of caregivers and experiments in macaques that appear to demonstrate high efficacy of post-exposure vaccination against monkeypox.
Smallpox vaccination prior to 1980 provides a priori immune protection against monkeypox of uncertain extent and duration.
“According to studies, for example, in the 2000s, antibodies against smallpox were found in 30% of people vaccinated at least 20 years ago,” says researcher Pasteur. And “a booster dose activates memory cells – B- or T-lymphocytes – and reactivates cellular immunity even after 20 or 40 years.”
However, Yannick Simonin cautions that immunity “weakens over time and that the resistance of neutralizing antibodies against monkeypox has never been assessed.”
– Which exit?
The only vaccine currently approved against monkeypox is produced by the Danish company Bavarian Nordic from the viral strain MVA-BN (modified vaccinia virus Ankara).
It is sold as Jynneos in North America and Imvanex in Europe.
Several countries and the WHO are stockpiling smallpox vaccine for safety, especially in the face of the risk of bioterrorism. Bavarian Nordic partnered with the US authorities in 2003 and has already supplied them with 30 million doses. After the current outbreak of monkeypox, the 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, that will take several months to use before being bottled. It is difficult to know the status of the stockpiles of countries opposed to military secrecy, to the chagrin of associations and elected officials.
We also do not know the details of orders from the only operating manufacturer. To date, the EU has 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 US lab that manufactures ACAM2000, told AFP that it has an annual production capacity of 18 million doses, which could reach 40 million doses per year if needed.
– What distribution?
Despite having monkeypox-endemic areas on part of the continent, more than 3,000 confirmed cases, and doctors estimate more than 70 potential deaths, there is still no dose of vaccine in Africa.
The WHO has asked countries that have vaccines to “share them with countries that don’t,” urging them not to replicate the Covid-19 scenario where rich countries kept almost all vaccines in stock for many months.
“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 Sunday. at the International AIDS Conference.