Four questions about vaccine efficacy declining over months

Four questions about vaccine efficacy declining over months

Shields are less effective than expected. Major vaccines against Covid-19 suffer a decrease in their level of protection over the months, according to a series of recently published scientific studies. This observation has already prompted some countries, including Israel, the United States and France, to announce campaigns to promote vaccination. What vaccines are affected? What causes this decrease in the immune response? What are the possible solutions? Franceinfo answers four questions raised by these studies.

1Do all vaccines lose their effectiveness?

This appears to be confirmed by the latest scientific studies, even if the results may differ slightly from one publication to another, due to methodological differences. Some surveys, for example, relate to periods when the delta variant, the most contagious, was not yet in the majority. Others do not distinguish between people who received only a first dose of the vaccine and those who were fully vaccinated. To determine the percentage efficacy of a vaccine, researchers typically calculate the relative risk of infection and disease, by comparing the vaccinated and unvaccinated, as shown. This analysis for Lancet (link in english).

For messenger RNA vaccines, such as those from Moderna and Pfizer-BioNTech, The US Centers for Disease Control and Prevention (CDC) estimates, In his last study (link in english) Published Tuesday, their rate of protection drops slightly over time, from 85% after four months of vaccination to 73% after five months. But these averages, calculated since December 2020, are at best a general picture.

The AstraZeneca vaccine, which protects less against infection than the Pfizer-BioNTech or Moderna vaccines, is more time-resistant and a Delta variant than its competitors, a study published on August 19 by Oxford University (which co-developed the AstraZeneca vaccine). analytics, Which hasn’t yet been peer-reviewed, you think This vaccine protects by 67% after one month, 65% after two months and 61% after three months. Four to five months after receiving both injections, the level of protection given against them COVID-19 The study concluded that it is similar to the Pfizer-BioNTech vaccine.

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This drop could also affect Johnson & Johnson’s single-dose Janssen vaccine It is the least used in France, According to Public Health France. a Study American University in New York (link in english) Posted mid-July already refers to a ‘Eloquent drop’ The efficacy of this vaccine is against the delta variant. Note shared in France by Haute Autorité de santé, which confirms its location The Lack of data available to confirm long-term efficacy” Janssen’s vaccine against this more contagious variant.

2What caused this decrease in efficiency?

Scientists pointed to the first factor: the emergence of a delta variant, more powerful and transmissible. The study already published by the US Centers for Disease Control and Prevention estimates the effectiveness of the Pfizer-BioNTech and Moderna . vaccines It has fallen from 91% to 66% since the delta variant became the majority in the United States. Other surveys conducted around the world confirm this weakness in the face of the delta variant, even if the numbers differ from study to study, and depending on vaccines. A worrying trend for many countries such as France, where this alternative is by far the majority.

In addition, it has been observed that vaccines seem to lose their effectiveness after a few months, as we demonstrated for example on August 19. reconsidering temper nature (article in English). a A study by Israeli doctors and researchersAnd conducted on more than 33,000 vaccinated people,Published in early August, it is estimated that The probability of infection increases significantly from 146 days after full vaccination. In France, the Haute Autorité de santé (HAS) is reassuring. This decrease in vaccine efficacy is gradual and moderate over time.”, confirmed to franceinfo its president, Dominique Le Golodic.

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Important note: This decrease in the rate of protection from vaccinations is mainly felt in people over 60 years of age. “Immunity decreases over time in the elderly, Tuesday called in France Inter Jean-Paul Ortiz, President of the Confederation of French Medical Syndicates. We know that they make fewer antibodies, and that the vaccine takes less.“It is the combination of these three factors (difference, time, and age) that has significantly enabled HAS to create categories of the population at risk for the recall campaign it advocates.

3Does this call into question the interest of vaccination?

No, according to the scientists behind these studies. “lamreduce inflammation [par le Covid-19] The remaining two-thirds confirm the continued importance and usefulness of vaccination., for example commented the authors of the survey published Tuesday by the US Centers for Disease Control. For Dr. Quinn Boyles, who was involved in the AstraZeneca vaccine study, the notable decrease in protection remains “very light”and does not in any way call into question its overall efficacy.”very high” Vaccines against severe forms of the disease.

A view shared by the US CDC, which was published on Tuesday Another study (in English) Performed on patients in Los Angeles from early May to late July. In this survey, the Network of Federal Agencies showed that unvaccinated people were about 5 times more likely to become infected and 29 times more likely to be hospitalized than those who were vaccinated.

4What are the solutions to this problem?

To counteract this relative decline in efficiency, laboratories and health authorities are currently agreeing on one measure: to organize a recall campaign. Despite the WHO’s reservations on the subject, several countries have already planned to inject an additional dose of the vaccine in the coming weeks. In France, HAS on Tuesday ratified the principle of the government’s desired no-confidence campaign that should begin this fall. This campaign, which will only use messenger RNA vaccines, currently concerns those over 65 as well as those considered at risk, that is, at least 15 million people in France, according to the head of HAS.

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In the long term, a vaccine update could be considered, but only if a new alternative justifies it, Ugur Sahin, co-founder and director of BioNTech, explained in early August. “A decision now may turn out to be a mistake if another formula prevails in three or six months”, then the specified The head of the German laboratory who considers the booster dose adequate protection.

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