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Covid France: Immunity possible if 50-60% get vaccine

With vaccinations starting on Sunday, doctors say collective immunity is possible even if 100% of people in France do not get the Covid vaccine

24 December 2020
Two vials of Covid vaccine. Covid France: Immunity possible if 50-60% get vaccineDoctors have said the success of the vaccine depends on keeping the R number below 1
By Joanna York

Leading doctors in France have said that mandatory vaccination is not necessary as collective immunity is possible even if not everybody in France ends up getting the vaccine.

Dr Karine Lacombe, infectologist and head of infectious diseases at Saint-Antoine hospital in Paris, told news source BFMTV that, with a vaccine that is 95% effective: “If 50-60% got vaccinated it would be sufficient to immunise the whole population.” 

Vaccination is thought to be an effective strategy against the Covid-19 virus, as immunising people against the disease through vaccination reduces the number of hosts who can catch and spread the virus. But polls have shown that people in France are less likely to get the vaccine than anywhere else in the world.

Read more: Covid vaccinations in France to begin on Sunday

Vaccine success depends on R number

Professor Jean-Stéphane Dhersin, epidemiologist and deputy director of mathematical science at research centre CNRS, told BFMTV that the percentage needed to get the vaccine is closely linked to the R number.

He said: “In terms of collective immunity, it is hard to know where we are because it depends on the R number being below 0. We must make sure that the R number does not rise above 1. [Then] to ensure collective immunity, we need to be in the region of 60% of the population being immunised.”

Official figures show that the current R number in France is 1.03. This means that every person who gets infected with Covid-19 will go on to infect 1.03 other people.

Figures from national ministerial statistics centre DREES show that 11% of the population (6.33 million people aged over 15) in France have had Covid-19. While having had the virus does not guarantee immunity, cases of reinfection are rare, so this 11% can be considered immune to the virus.

Professor Dhersin said: “Now we are at over 10% [immunity], but if we have effective vaccines that could rise up to 55%, then we would be between 50-60% and collective immunity would be reached.”

But other doctors are taking a more cautious view. Professor of Virology at la Sorbonne, Vincent Maréchal, told BFMTV that current projections were all based on “hypotheses”.

He said: “We still do not know if the vaccine blocks transmission of the virus. We know that it stops illness and serious cases. [But] the polio vaccine does not stop transmission of the virus.” 

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