While the Minister of Health Olivier Véran has just announced that the 2and reminder (or 4and dose) of the vaccine against covid-19 was now open to people over 60, the Research, Studies, Evaluation and Statistics Department (DREES) just published the results of a large study on the protection conferred by the injection of the first booster dose, depending on whether it was carried out less than or more than three months ago.
This study, which relates to the population of 40 years or more, indicates that beyond 3 months, the vaccine effectiveness of the 3rd dose is eroded but that it remains effective against the severe and serious forms, and the hospitalizations remain significantly lower compared to non-vaccinated people. “The booster dose provides renewed protection against severe forms for 40-59 year olds, 60-79 year olds and 80 year olds or over, with vaccine protection against hospitalizations and deaths of between 75% and 90% in the 3 months following its injection. The protection nevertheless erodes after 3 months, while remaining significant: between 65% and 85%” underlines the DREES.
Immune memory erodes over months
“The hindsight now acquired thanks to clinical trials and real-life observations (in Israel) shows protection for at least 6 months in most people who have benefited from a complete vaccination schedule”, explained the Ministry of Health. Health in a press kit of December 3, 2021. The problem is that beyond 6 months, vaccine effectiveness erodesas proven by numerous real-life data, particularly in the elderly and frail, as recalled by the High Authority for Health (HAS), in its opinion of August 23, 2021.
“What’s Classic”, explained Olivier Véran, the Minister of Health during a press conference on November 25. “The vaccine learns to make antibodies to prevent you from infecting you. But immune memory is not infallible, hence the reminder to reactivate immune memory and multiply immune efficiency”. This gradual reduction in protection essentially concerns efficacy against infection and against symptomatic forms“effectiveness against severe forms remaining at a high level, regardless of the vaccine administered”, also underlines the Ministry of Health.
The booster dose had therefore been extended to all adults and the period for benefiting from it had been reduced to 5 months, due to the acceleration of the epidemicat the end of the year.
From when are we protected with the 3rd dose?
This booster dose, which must be of an mRNA vaccine (Pfizer or Moderna for those over 30, only Pfizer for those under 30), reactivates antibodies which gradually decline over time.
According to a study published on November 30 in the scientific journal Jama Internal Medicine, the booster dose reaches its maximum effectiveness after 14 days after the injectionand it lasts up to 65 days post-infection (the study does not have data beyond that).
This study is based on data collection in Israel where the booster has been recommended since the end of August 2021.
In detail, more than 300,000 people over the age of 40 were followed for 65 days. They were divided into two groups: either classic vaccination scheme (2 doses of the vaccine Pfizer), or a booster dose (Pfizer). Scientists have tracked the proportion of PCR tests positive in both groups. Here are the results :
- in the “complete vaccination schedule” group, 6.6% tested positive.
- within 6 days of the booster dose, the risk of testing positive is comparable to that of people who did not receive it (6%).
- between the 7th and 13th day, 3% tested positive.
- it is from the 14th day that the effectiveness is real: 1% of positive tests only, and up to 0.7% at 28 days, confirming that the protection conferred by the booster dose gradually increases over time.
Positive rate of PCR tests after injection of the booster dose of the Pfizer vaccine:
What confirms Étienne Decroly, research director at the CNRS, in the columns of Parisian this December 10. He explains that there are “a clear difference after the 7th day”while emphasizing thatit is not an “on/off” button. “Some will be well protected on the 5th day, others on the 8th”.
Anne-Claude Crémieux, professor of infectious diseases at the Parisian hospital Saint-Louis, also questioned by our colleagues from Parisian, is even more cautious. “Be careful, the maximum protection is reached between fifteen days and three weeks”.
Hence the need, in the meantime, to continue to respect barrier gestures.
Read also:
- Variant Omicron: should we fear it? Will the vaccines be effective? The expert’s answers
- Why do children have fewer severe forms of Covid-19?
- Vaccine for 5-11 year olds (Covid-19): calendar, obligation… We take stock
- Variant Omicron: symptoms, efficacy of the vaccine, cases in France… What we know
Sources:
- Booster dose, Ministry of Health press kit, December 3, 2021.
- Odds of Testing Positive for SARS-CoV-2 Following Receipt of 3 vs 2 Doses of the BNT162b2 mRNA Vaccine, JAMA, November 30, 2021.
- Olivier Véran press conference, November 25, 2021.
- HAS opinion of August 23, 2021.
- Le Parisien, December 10, 2021.