In the context of an epidemic resumption, many scientists consider that it is indeed time.

But some express reservations, knowing that the vaccine in two doses remains very effective against severe cases of the disease and death.

Update on the different arguments.

Why now?

Recalls have been a point of contention among experts.

An advisory committee of the American Medicines Agency (FDA) had voted in September against a recall accessible to all, and tightened the eligibility criteria to certain categories of the population only (the oldest, fragile or exposed).

What has changed in the meantime?

For Vincent Rajkumar, professor at the Mayo Clinic in Rochester, in the US state of Minnesota, one of the main new arguments is the clinical trial conducted by Pfizer on 10,000 people aged 16 and over.

He showed that the efficacy after a booster dose rose to 95.6% against symptomatic forms of the disease.

There is also the example of Israel, which fought the wave caused by the Delta variant with a massive recall campaign.

More recently, UK data on people over 50 showed that the effectiveness of the vaccine after a booster dose exceeded the level of protection achieved after the initial two doses.

"The purely scientific answer to the question + do the callbacks work? + Is yes, there is no doubt," asks the professor.

He also says he is worried about the cases of Covid-19 in vaccinated people.

Although they are much less likely to die or be hospitalized, new data in Minnesota shows that "deaths among those vaccinated are not zero."

Currently: about one death per 100,000 people per week (compared to 14 per 100,000 among unvaccinated people).

Those most at risk of dying despite their immunization are the oldest and those who are immunocompromised, such as those with cancer or who have had an organ transplant.

"If I get sick even though I'm vaccinated, it's a risk for them - and that's why if I'm not infected, it's a good thing," says Vincent Rajkumar.

- Reserves -

Not all experts are so enthusiastic.

Celine Gounder, an infectious disease specialist and professor at New York University, would like to see more evidence of long-term acquired immunity with these boosters.

For her, the debate stems from the lack of consensus around the desired goal: "Are you trying to prevent severe cases, hospitalizations and deaths? Or are you trying to prevent infection and transmission?"

But in both cases, reminders are not necessarily the most suitable response, according to the specialist.

The best way to reduce the most serious outcomes is to reduce the rate of transmission by vaccinating the unvaccinated.

And everyone already agrees that the elderly or immunocompromised, the most at risk, receive a booster.

For Celine Gounder, it is also unrealistic to think that the reminders will block all transmission, in particular because of the rapid incubation period of the virus.

Promoting a booster dose may also be counterproductive to skeptics, who tend to conclude that vaccines are ineffective.

Another risk is the increased number of myocarditis after injection of a messenger RNA vaccine, especially among young men (a side effect which remains rare).

The specialist does not exclude supporting a series in three doses for all at one time, or another combination (two doses more spaced, regular reminders ...).

But according to her, this needs to be studied more comprehensively.

- Equity -

Experts agree in any case that recalls alone cannot put an end to the pandemic, at a time when the poorest countries, especially in Africa, are still at a very low vaccination rate.

Last week, the Director-General of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus, was offended that there are six times more booster doses injected in the world every day than the number of doses initial injections daily in low-income countries.

"It would be really deplorable if after all our vaccination work, we found ourselves going back because of a variant emerging elsewhere in the world," notes Celine Gounder.

© 2021 AFP