Monkeypox: how the vaccine that is applied today in the world works

The current vaccine against monkeypox is called JYNNEOSTM, also known as Imvamune or Imvanex, which is produced by the Danish pharmaceutical company Bavarian Nordic.

Unlike what happened with the coronaviruswhen the monkey pox suddenly began to spread around the world last May, The world was fortunate in one respect: it already had a vaccine available against this disease.

The MVA vaccine is called JYNNEOSTMalso known as Take it down o Imvanexwhich is produced by the Danish pharmaceutical company Bavarian Nordic as a smallpox vaccine, it was already licensed for use against monkeypox in Canada and the United States.

Since then, the regulators of the European Union have followed suit, have approved it and are currently applying it given the extent of infections on that continent and the recent declaration of the international disease emergency monkey pox by the World Health Organization (WHO) that put all health systems on alert to try to stop the outbreak that escaped from Africa and where it has been endemic for 50 years.

A person receives a dose of Jynneos vaccine at Spallanzani Hospital, as monkeypox vaccination kicks off in Rome, Italy.  August 8, 2022. (Spallanzani Hospital/Handout via REUTERS)
A person receives a dose of Jynneos vaccine at Spallanzani Hospital, as monkeypox vaccination kicks off in Rome, Italy. August 8, 2022. (Spallanzani Hospital/Handout via REUTERS)

while there is already 89 countries affected, with more than 32,000 infected, according to the last count of the Centers for Disease Control and Prevention (CDC)from USAthe health authorities of each country are requesting vaccines against this disease.

Vaccine supplies are limited and no doses have been shared with countries in Africa that have been affected by monkeypox for a long time. But in Europe and North America, clinics have already delivered thousands of doses to people in high-risk groups.

There is no doubt that the vaccine can help, but scientists still cannot know exactly how well MVA protects against monkeypox and for how long. It is also unclear how much protection is lost by giving a single dose instead of the recommended two doses, as some countries are doing to stretch supply, or how much protection a vaccine given after exposure may offer.

Placebo-controlled clinical trials are complicated because MVA is already licensed and people are clamoring to get it. Y vaccine clinics are often set up at short notice as doses become available, making it difficult to organize a trial and enroll subjects. Researchers are responding with a plethora of ingenious trial designs.

Specialists provide new recommendations for the population in the face of the outbreak of cases.
Specialists provide new recommendations for the population in the face of the outbreak of cases.

The first evidence that smallpox vaccines also protect against monkeypox came from a study in the 1980s in the Democratic Republic of the Congo (then called Zaire), where the virus occasionally jumps from animals to people. who then infect others in their household.

A study among patient contacts suggested that smallpox vaccination was also 86% effective in preventing monkeypox. But the study looked at a small number of cases, the virus was genetically quite different from the one now spreading, and the smallpox vaccine was older with more side effects. Now, the new MVA has been developed as a safer and licensed alternative to monkeypox based on data from animal experiments and the immune response it triggers in humans.

But its effectiveness has hardly been proven in people, and not at all in preventing sexual transmission, which results in a very important exposure of the mucous membranes, which is not the same as rubbing someone,” explained Dr. Anne Rimoin, an epidemiologist at the University of California, Los Angeles.

Until now, there is little data on how well the vaccine is working in the current outbreak. Among 276 people who received an injection at a Paris hospital as post-exposure prophylaxis (PEP) after reporting a high-risk contact, 12 developed a monkeypox infection, French scientists described in a scientific study from recent preprint, 10 of them within 5 days after vaccination and two after more than 20 days. “That some people develop monkeypox a few days after becoming infected is not surprising. The vaccine is not a miracle, it takes time to be effective”, said Dr. Jade Ghosn of Bichat Hospital, who led the study.

The vaccine is not a miracle, it needs time to be effective, experts warn, after seeing infections 20 days after it was applied
The vaccine is not a miracle, it needs time to be effective, experts warn, after seeing infections 20 days after it was applied

But the two cases occurring 22 and 25 days after vaccination are a surprise, especially since no additional high-risk contacts could be established.) Nevertheless, the study did not have a control group, so it is impossible to say how many people would have developed monkeypox if no one had been vaccinated. And people eager to get vaccinated may have lied about having a high-risk contact. “That makes the results of these PEP studies really difficult to assess,” said immunologist Leif Erik Sander of the Charité clinic in Berlin, who is organizing a vaccine study in Germany.

A randomized trial, in which one group receives the vaccine and the other does not, would avoid such problems. “Without a randomized study, you may end up in this evidence limbo and find that if you had done the trial, you would have been in a much better situationadded biostatistician Natalie Dean of the University of Florida.. Giving a control group a placebo instead of a presumed effective vaccine is ethically risky, many researchers say. But Oxford University epidemiologist Richard Peto sees another way. Because the demand for the vaccine is so much greater than the supply, “why not randomize the order in which people in the highest-risk group are called?” Pet asks. So far, however, no one seems to have bought into that idea.

Groups may differ in ways other than their vaccination status (people with many sexual contacts may make more of an effort to get vaccinated, for example), But there’s still an element of randomization, Sander says: Many doctors use lottery-type procedures to decide who gets vaccinated first. A cohort study in France is taking another approach.

The US National Institute of Allergy and Infectious Diseases (NIAID) plans a randomized trial of the vaccine
The US National Institute of Allergy and Infectious Diseases (NIAID) plans a randomized trial of the vaccine

There, those who are enrolled in a study of sexually transmitted diseases, and who are considered to be at high risk of contracting monkeypox, will receive MVA in the next 2 months. Ghosn, who is leading the study, expects all participants to be vaccinated by the end of September and plans to compare infection rates before and after vaccination.

Another option is a “test negative” design, in which researchers look at people seeking the monkeypox test and compare the percentages of people who were vaccinated between those who tested positive and negative. “This is probably the strongest non-randomized approach to measuring vaccine efficacy,” says Michael Marks, an epidemiologist at the London School of Hygiene & Tropical Medicine who is planning a vaccine trial soon with colleagues in Spain.

The negative test setup requires good linkage between vaccination and test data. “If we can solve that problem, we can use such a design in our study,” says Marks. The Canadian province of Ontario is moving ahead with a similar design, says Jeff Kwong of the University of Toronto. The downside is that testing and vaccination data alone can’t answer many other questions, such as how immunity develops over time or whether disease severity is different between the vaccinated and the unvaccinated; which requires additional studies.

The US National Institute of Allergy and Infectious Diseases (NIAID) plans a randomized trial, with the aim of finding out if the supply of vaccines can be stretched by giving people much smaller doses.

“Participants will receive either two full doses or two fifth doses 4 weeks apart. A third arm can be added to test a tenth of the normal dose,” said Dr. John Beigel of NIAID, who is involved in the study design. The lower doses will be injected into the skin, which is known to elicit a more vigorous immune response than the standard subcutaneous injection. But the study, which is expected to start in September, will only test whether the fractional doses trigger a similar immune reaction as the full dose; it will not measure the efficacy of the vaccine directly.

“One strategy that was not tested in the trial, although it is being used, is to give only one full dose. Available data suggest that the regimen is less than two full doses. We do not believe that it is scientifically supported,” Beigel concluded.

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