Doses of the Pfizer / BioNTech vaccine are shipped on December 27, 2020. -

Thomas Samson / AP / SIPA

  • The first vaccine against the coronavirus to have been authorized in Europe, developed by the Pfizer and BioNtech laboratories, has the particularity of being inoculated in two doses three weeks apart.

  • The United States will respect the recommendations resulting from the clinical trials of the manufacturers, explained the doctor Anthony Fauci.

    This is not the strategy adopted by the United Kingdom, which is facing a more contagious variant of Covid-19, nor that of Denmark, which chose to delay the second injection in order to vaccinate, even partially, a larger number of persons.

  • According to Public Health England, the British public health agency, the effectiveness of the vaccine is 89% 15 to 21 days after the injection of the first dose.

    It rises to 95% after the second injection.

Is there a risk of reducing the effectiveness of Pfizer and BioNTech's vaccine against Covid-19 by delaying the injection of the second dose?

While the two laboratories recommend making the second injection 21 days after the first, several countries have chosen to postpone the injection of this second dose in order to provide coverage, even partial, to a greater number of their citizens.

This is notably the strategy adopted by the United Kingdom, where vaccines can wait up to 12 weeks before receiving the second dose, and in Denmark, where this period can be extended to six weeks.

Germany could also adopt this strategy.

BioNTech issued a warning Monday, warning that "the vaccine's efficacy and safety have not been evaluated for other dosing schedules."

The vaccine's effectiveness is 89% 15 to 21 days after the injection of the first dose, according to Public Health England, the English public health agency, as cited by the

British Medical Journal

.

It rises to 95% after the second injection, according to clinical trial data.

In a context where the demand for the vaccine currently exceeds the delivery capacities, several specialists have looked into this question.

Experts from the WHO immunization group recommend administering the second dose "within 21 to 28 days", but that it could be delayed "in exceptional circumstances of epidemiological contexts and drug constraints. supply ”.

Kate O'Brien, director of the "immunization and vaccination" department of the international organization, warned, however, that this delay could not exceed six weeks.

In the United States, Dr. Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases, said on January 1 in an interview with CNN that his country would follow the recommendations from clinical trials.

On Monday, it was the FDA's turn to recommend following the manufacturers' recommendations.

The federal body, responsible for authorizing the marketing of drugs, warns that a change in the administration of the second dose, whether for the Pfizer vaccine or that of Moderna, which has just been approved by the European Medicines Agency, and also requires a second dose after 28 days, is "premature" and "not firmly anchored in the available evidence".

The European Medicines Agency recommends not to exceed 6 weeks

The US agency adds that 98% of participants in clinical trials for Pfizer-BioNTech vaccine and 92% of those in trials for Moderna vaccine received a dose after 21 or 28 days respectively, not knowing which would be the effectiveness of the first dose beyond these times.

The European Medicines Agency, for its part, recommends not to postpone the injection of the second dose beyond 42 days (six weeks), reports the Reuters news agency.

Debate between doctors in the United Kingdom

In the United Kingdom, the decision is debated.

An association of British doctors highlighted several difficulties created by this postponement, including that of reorganizing appointments for elderly patients.

Independent SAGE, a group of doctors organized as a response to the scientific committee which advises the British government, however supports this change, stressing that the vaccination campaign is starting as a new variant of Covid-19 is spreading in the country.

This is "substantially more transmissible" than the earlier variants.

The pandemic is "out of control" and the British health system, the NHS, "is in trouble", they stress.

Vaccination of large numbers of people, as well as another set of measures, such as restrictions on movement, are, according to this group, the weapons to limit the spread of the new variant.

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