Tuesday, January 18

Covid-19. How the vaccine protects us (despite everything) against the fifth wave

The fifth wave is here, and there it is: faced with the surge in contamination which is beginning to threaten hospitals this winter, Olivier Véran must announce new “measures” on Thursday.

Is the vaccination that was supposed to avoid it, therefore, useless? Many think so, if it is to undergo a new epidemic wave so strong?

In reality, the situation is not that simple. And the situation varies a lot from one country to another, with almost only one variable: the vaccination rate.

From this point of view, France is doing very well, with more than 80% of the eligible population vaccinated. One downside, however: too little vaccination in … the most vulnerable: several hundred thousand people aged 65 and over have not received any dose of vaccine in France.

In Portugal and Spain, which have almost the same vaccination coverage, 100% of the oldest inhabitants are vaccinated.

The fifth wave amplifying delta variant

Vaccines against Covid-19 have been designed primarily to fight against severe forms. If they have been shown to be effective, with the “alpha” variant, against infections, this is no longer true today.

At least, not as much: vaccination only protects in one in two cases, or even in three, according to the latest available data. A vaccinated person can therefore be infected in two thirds of cases …

At issue: the delta variant, much more contagious, with a much higher viral load.

Despite everything, the best vaccinated countries remain much better protected, in terms of infections such as serious forms and deaths.

Thus, countries with low vaccination coverage experience a high level of contamination:

Likewise, in the most vaccinated countries, severe forms and deaths remain at a “sustainable” level – including when contaminations escalate, as in Germany or the United Kingdom.

In detail, we can also compare the different epidemic waves: in the United Kingdom last January, there were 60,000 contaminations per day on average. Which caused 1,200 daily deaths – 2.07% of the total.

In recent weeks, for 42,000 daily contaminations, there are no longer across the Channel “that” 140 daily deaths. Or 0.33%.

Mortality is therefore 6 times lower since generalized vaccination. And again: the United Kingdom has massively used the less effective AstraZeneca serum. The country has also lifted all other restrictive measures since July.

Alone, the vaccine is no longer enough

The vaccine does not fully protect against infection. Government communication has sometimes shown signs of wandering, suggesting that being vaccinated made it possible to do without barrier gestures, masks, social distancing.

As much as these arguments could be heard before the delta variant, they are obsolete today. The executive has also been widely criticized when ministers participated in unmasked events, indoors. Two members of the government, Prime Minister Jean Castex, and Minister Brigitte Klinkert, have also been infected with Covid-19.

This confusion was also fueled by a decree – dating from this summer – indicating that it was possible to abandon the mask in places subject to the health pass – while specifying all the same that the operator of the premises or the prefect could maintain obligation.

Immediately, scientists were alarmed by such a measure: according to them, it is important not to bet everything on vaccination, which is imperfect.

They advocate the now famous “Emmental theory”, according to which the effectiveness is all the stronger when all imperfect measures are added.

We can see the same thing in any country: in France, we went from 1.18% of deaths to 0.28%. And in Portugal, from 2.24% to 0.48.

Conversely, Bulgaria, where less than one inhabitant in three is vaccinated, has not seen its mortality rate drop.

On the other hand, the number of cases soared, going from 3,500 per day on average during the previous wave … to more than 5,000.

Because this is another demonstration of the increased transmissibility of the delta variant: when there is no vaccination, the number of contaminations explodes. And mortality follows.

In Germany, where only two out of three inhabitants are fully vaccinated, as in Austria, the number of daily infections has doubled between the current wave and the previous one.

A vaccine that strongly limits contamination and transmission

The vaccine limits contamination – like most vaccines. In doing so, it plays a role in the speed at which the virus spreads, and therefore in the extent of the epidemic.

Against the risk of infection, the vaccine is only 50% effective – or even 35% after six months. It would therefore prevent one infection in two, or even one in three.

If it seems low, this figure is not negligible: in an “unvaccinated” environment, if one person infects two, which each infects two, we already end up with seven infected people. And at 15 at the next stage (the initial patient, the first two infected people, plus the next four and another eight afterwards).

With the same group of people but all vaccinated, one in two contamination is avoided. The number of people infected then drops to just four – almost a division by four.

So much for the risk of infection. But the vaccine also limits transmission: with the delta variant, a vaccinated infected person is indeed as contagious as an unvaccinated one. But the infection lasts less: and by being contagious for two days instead of four, we infect fewer people.

Should we only vaccinate the most vulnerable?

As we have seen, vaccines against Covid-19 are not “sterilizing” – unlike that against measles, for example: having measles or being vaccinated against is enough not to be infected again.

Today, it is among young adults (20-39 years) that the incidence rate is highest, and among children and minors (0-19 years) that the increase in the incidence rate is the highest. stronger.

In one week, the incidence rate has doubled among 10-19 year olds, and nearly three times among 0-9 year olds.

These populations have little risk of developing a severe form of Covid-19. But they actively spread the virus, especially those under 12 who do not currently have access to the vaccine.

But the higher the vaccination coverage, the less the virus circulates, mathematically. Even if it prevents only one in two or three infections, each person vaccinated constitutes a potential “barrier”. Especially to protect the elderly and the most vulnerable, in whom vaccine protection is even less effective (immunocompromised, dialysis patients, transplant recipients, cancer patients under treatment, etc.)

Finally, even extremely rare, severe forms are not non-existent in the youngest: three quarters of the deaths of Covid-19 were over 75 years old, but nearly 10% were under 60 years old, as in the case of history of this Vosges family.


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