• Does Janssen keep its promise to be effective with just one dose?

    The question arises more and more after many cases of hospitalizations in people who have received this serum.

  • The National Medicines Safety Agency launched the alert on Monday, but the effectiveness of single-dose has been questioned for weeks.

  • "20 Minutes" takes stock of the situation.

The only coronavirus vaccine that requires only one dose, does Janssen provide a sufficient immune response?

The question arises after the hospitalization for Covid-19 of many patients yet vaccinated with Janssen.

An abnormally high rate for people supposed to be massively protected against hospitalizations and severe forms.

Studies had already shown that a second dose of Janssen significantly improved the immune response.

So, is one dose really enough? 

20 Minutes

 takes stock.

What proportion does the Janssen vaccine represent in vaccination in France?

The Janssen vaccine is based on the adenovirus technique, like AstraZeneca, and does not work with the messenger RNA technique unlike the two other coronavirus vaccines authorized in France, namely Pfizer / BioNtech and Moderna. It has been administered in France since April 24, 2021 and was quickly reserved for people over 55, according to the benefit / risk balance of AstraZeneca.

This vaccine has only been given to one million people in the country, making it by far the least used vaccine of the four.

In comparison, 7.8 million AstraZeneca doses were administered, 9.7 million Moderna and 72.6 million doses of Pfizer / BioNtech!

Admittedly, these other vaccines require two doses (except in the event of infection with the coronavirus, which still represents a significant number), but even by roughly dividing by two, the number of French people vaccinated with the other vaccines is much more important.

78% of French people vaccinated were vaccinated with Pfizer-BioNtech alone.

Why is the effectiveness of the Janssen vaccine criticized?

In a report published on Monday, the National Medicines Safety Agency (ANSM) is concerned about the abnormally high number of serious cases and deaths recorded by hospitals around Janssen single-dose vaccines. An “over-representation of patients vaccinated with Janssen” has been reported in two CHUs, those of Marseille and Tours. However, the vaccine is precisely supposed to protect massively against serious forms and death. Thus, 32 cases of Covid-19 infection have been reported in people who have received Janssen. More problematic, 29 of these cases required critical care, and 4 deaths are to be deplored.

These numbers are extremely high for people who are supposed to be fully immunized. Thus, according to the Directorate of Research, Studies, Evaluation and Statistics (DREES), for one million people fully vaccinated (i.e. the number of people who received a Janssen injection), regardless of the vaccine, the critical care rate for the week of August 9 to 15 was 3.7 people in critical care and 2.5 deaths. So far from the figures of Janssen alone.

In fact, Janssen has been questioning for many months. Doctor Franck Clarot reminds us: “Quite quickly, studies looked into the limits of such a single-dose system. Many researchers have wondered if this was not a marketing argument to the detriment of effectiveness, especially when we saw the effects in real life of the importance of the


of the second dose. "

Thus, from August 23, the High Authority of Health (HAS) recommends that a booster dose by an mRNA vaccine be offered to Janssen vaccinated from 4 weeks after the first injection, in the name of "the insufficient protection conferred by a single dose of vaccine against symptomatic forms associated with the Delta variant, and the lack of available data to confirm the long-term efficacy of the one-dose vaccination schedule of the Covid-19 Janssen vaccine against the Delta variant. "

However, several biases can be at work, warns Franck Clarot.

As the vaccine is only available to the elderly, it is normal for severe forms and deaths to be greater in this population than in all vaccinees, even if such deviations are abnormal.

Then, "the population vaccinated with Janssen is mostly skeptical about vaccines and the coronavirus, which is why they favored this single dose, there may be more risky behaviors, but also false vaccinations, given that a health pass to one dose is easier to forge than a pass with two doses.


Will a second dose be essential?

"Further investigations" will be carried out to verify if the failures are more important with Janssen, or if it is only about bias.

As already said, the HAS already recommends a second injection of messenger RNA vaccine.

“We think that the vaccine mixture can increase the effectiveness of these, but if we really want to give a second systematic dose after Janssen, that will require studies and choices.

It is still too early to know, ”notes Franck Clarot.

Note that the Janssen vaccine is almost no longer administered in the first dose in France, just like AstraZeneca.

The overwhelming majority of first-time injections are with RNA vaccines, Moderna and Pfizer-BioNtech, which represent more than 95% of the first doses administered during the past week.


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  • Covid 19

  • epidemic

  • Anti-covid vaccine

  • Janssen

  • Vaccination

  • Coronavirus

  • Health

  • Vaccine