The authorities want to vaccinate at least 70% of the population against Covid. But some Belgians are reluctant to see products developed very quickly. The epidemiologist Marius Gilbert explains to us the path that awaits us.
The good news about vaccines against Covid follows one another. Those developed by Pfizer and Moderna could be available at the end of this year. And several candidates demonstrate an efficiency greater than 90%.
In Belgium, we hope to administer the first vaccines in March. And thegoalis that 70 to 80% of the population accepts the injection. But that is clearly not won. According to Sciensano, 50% of the population intends to be vaccinated, 33% are not sure they will and 17% do not intend to.
“If the rate of the vaccinated population is less than 70%, we will keep a strategy that will combine hygiene measures, social distancing …”
It is therefore we may not reach this 70%. That more than half of Belgians refuse. That the operation meets with massive enthusiasm in Flanders, but not in Wallonia. That the old people accept, but that the young people steer … In this case, we forget the return to our life before?
Reduce the reproduction rate of the virus
“We know thatin the absence of any control and prevention measures, the R0, reproduction rate of the virus, is 4“, recalls Marius Gilbert, epidemiology researcher at the Free University of Brussels. On average, an individual contaminated by Covid will infect 4 others. This phenomenon gives rise to an exponential growth in the number of transmissions.
“Therefore, if we want to prevent the spread, it is necessary that each contaminated person infects less than one, that the R0 is brought back under 1. Which means that of the four people encountered by the infected individual, three must be vaccinated. “It’s mathematical: 70 to 80% of the population must be protected. It seems simple. And if the distribution of the vaccinated population is homogeneous, it is ideal.
The individual and collective role of a vaccine
But this is where a big unknown comes in. An effective vaccine prevents infection from the person who received it. This is what we ask him and what the various promising candidates seem to be doing well: there are fewer patients among the vaccinated than in the placebo group. This is the protective function of the vaccine, at the individual level.
“Some vaccines are just protective and don’t stop the spread!”
But’a vaccine is also expected to be effective for prevent spread. This is the collective benefit. This one is still guaranteed for no vaccine against the Covid, for lack of perspective. A vaccinated individual could indeed remain a carrier of the virus …
“We suspect that a healthy person has a lower viral load and is arguably less infectious. But this is not always the case. Some vaccines are just protective!“, specifies Marius Gilbert.
A strategy to refine
Or, of this capacity, or not, to break the chains of transmission the vaccination strategy will depend. The attitude of the health authorities to the degree of support from the population will have to be adjusted according to this still uncertain element.
With a vaccine that would only prove to be protective, “If young people generally reject it but the elderly accept it overwhelmingly, it will not be very serious because the latter will be well protected. older people who are not vaccinated face an increased risk“, since the circulation of the virus in the population would not be slowed down, warns the epidemiologist from the ULB.
More if, in addition to protecting the vaccinee, the injections cut off the of Sars-CoV-2, vaccination of the least vulnerable, young people in particular, would be precious to solve the public health problem.
“In September-October, the R0 was 1.5. It would then have been enough for 20 to 30% of the population to be vaccinated to bring it down to below 1.”
More reluctant francophones
Vaccination could be refused in certain socio-cultural groups with a mixed age. What to do then? Confining only these groups? “No, it will take communicate more and better about the benefits of vaccination!”, implore Marius Gilbert.
So, what will happen if only 20% or 30% of Walloons accept the vaccination? Such a prospect is possible since francophones would be more reluctant, driven by the strong anti-tax movement which is booming among French neighbors.
“We are controlling the situation first with non-pharmaceutical measures as at present, and then, the advance of vaccination will allow these to be relaxed.”
Marius Gilbert recalls that the goal remains to keep an R0 lower than 1, and it will therefore be necessary to modulate the measurements according to this data. “Things can combine. For example, when the epidemic resumed in September-October, the R0 was 1.5. It would then have been enough for 20 to 30% of the population to be vaccinated to bring it down to below 1. If the rate of the vaccinated population is less than 70%, we will keep a strategy that will combine hygiene measures, social distancing… “
If there difference in vaccine acceptance is really important between regions, these can still apply different tactics, as is the case now, with different curfew times between Wallonia and Brussels on the one hand (10 p.m.-6 a.m.) and Flanders (midnight-5 a.m.) on the other.
The principle of the balance
“We will have to continue to combine strategies for a while if we do not have enough doses,” warns Marius Gilbert. Vaccinate 8 million Belgians will not happen anyway not in a few weeks, especially since the different vaccines that will be purchased by our country will not be not available at the same time. “Having between 25 and 30% of our population vaccinated would already make it possible to reduce the number of rules necessary to keep the R0 below 1.”
The ULB researcher uses the image of the balance to explain the principle. “We can relax the rules gradually as the vaccination progresses. We control the situation first with non-pharmaceutical measures, as at present, and then, the progress of the vaccination will allow these to be relaxed while keeping the value below 1. “This will make it possible to reduce and then keep at a low level the burden on hospitals.
This principle of balance could prove to be a good communication tool when it comes to convincing the Belgians of the usefulness of the injection. But we will have to, once again, succeed in s’adresser the targeted to different audiences. It didn’t not been the strong point of our authorities since the start of the crisis. “But it is difficult to already develop a strategy. We must remain attentive to the evolution of clinical data and launch preparatory work. In fact, communication has already started, via pharmaceutical companies“, slips the epidemiologist of the ULB.
The arguments of antivax
The reluctance of the population is not a cost issue: the injection will be fully reimbursed. But antivaxers claim that big pharma has a conflict of interest, between big money and health. “These are poorly supported arguments, it testifies to a poor knowledge of medical reality”, answers Marius Gilbert.
“There are side effects with some vaccines. But the frequency is low.”
The Mediator case had, of course, added fuel to the fanatics’ fire. “But that’s not why the pharmaceutical companies are all thugs! We must not be naive, the economic stakes are major. But the competition and the fact that there are many tracks can only benefit public health.”
In addition to the irrational fears fueled by particularly inventive conspiracy theories that some Belgians may have, there is still the safety issue. “There are Side effects with certain vaccines. But the frequency is low, we are talking about 1 in 1,000. For Covid vaccines, the current data are reassuring, especially as studies are carried out on huge groups, from 30,000 to 40,000 people. But it’s very short term, this assessment must be based on clinical data. This is why, even if we are in a race against time, we should not rush, “tempers the ULB scientist.
Can Sars-CoV-2 go away?
Can we hope for the eradication of the virus if 80% of the population accepts vaccination, in Belgium and elsewhere? Few scientists believe in the death of Sars-CoV-2. “Apart from smallpox, there aren’t many examples of vaccine eradication“, recalls Marius Gilbert. A priori, I do not think we can eradicate this new coronavirus, but it is still too early to say it. It will also depend on the duration of the immunity offered by the vaccines.”