To fight against monkeypox, the Imvanex vaccine, already authorized by the European Commission, is eagerly awaited in Switzerland. But is this vaccine administered until the 1980s to fight classic smallpox really effective?
A consultation has been launched in the cantons and the Confederation should soon decide on the authorization in Switzerland of the Imvanex vaccine.
This vaccine was developed in the late 1970s to initially fight classic smallpox, the human form of the disease. It is a cousin of monkey pox which has been eradicated since the 1980s worldwide.
The idea of the health authorities at the time was to prepare for a resurgence of the disease by developing a modern vaccine, with the fewest possible side effects.
But since, at the end of the epidemic, there were no longer any cases of human smallpox, we tested this new vaccine on the animal variant of the disease, namely the famous monkeypox which is currently spreading in the human population.
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Ideally two doses one month apart
And what the studies carried out on primates show is that to obtain effective protection, both for the severe forms and for the spread of the virus, it is ideally necessary to inject two doses of vaccine one month apart.
“After one dose, the antibody level is at its peak at 14 days. But after that, it will go down”, explains Thursday in La Matinale Frédérique Jacquerioz, assistant doctor at the Center for Emerging Viruses at the HUG. “So it’s the fact of giving two doses as a primary vaccination that will provide the best protection.”
But obviously, she points out, there are a lot of possible extrapolations, because these studies have not been done on humans. “Afterwards, it’s a question of knowing what is the best strategy knowing that a dose protects less well, and according to what you want to obtain in terms of public health.”
Faced with the lack of availability of the vaccine, some countries like France have decided to space out the injections in order to be able to immunize as many people as possible. In Switzerland, once the vaccine is available, it is not yet known what strategy will be adopted. This will depend above all on the number of doses that the Confederation manages to obtain from the Danish company Bavarian Nordic.
Other vaccines?
The ideal would be to develop other vaccines specially dedicated to this disease in parallel, as was the case for example with the coronavirus. However, for EPFL virologist Didier Trono, it would be difficult to launch research. Especially since the vaccine available has a good chance of working.
“Developing a new vaccine is extremely expensive. Often this discourages any attempt to come up with these new vaccines,” he explains.
Not to mention that, according to the virologist, the chances that monkey pox will evolve are very low, unlike, for example, the coronavirus and its many variants. As he explains in La Matinale, monkeypox is indeed a virus with much more stable genetic material than the coronavirus.
“Since monkeypox spread on a larger scale in the human population, we followed the sequence and found that it did not change much. There is a kind of micro-evolution but nothing nothing that could in any case make us think that this virus will evolve differently from that of classic smallpox which is so stable that it could be eradicated.
Other vaccines older than Imvanex exist, but they are riskier and have more side effects. And they haven’t been tested on monkeypox at all. There is therefore little chance that they have come out of the drawers to fight against the current epidemic.
Sophie Iselin/fg