Fewer cases to aim for herd immunity?

Herd immunity, which would halt the proliferation of the new coronavirus, could be reached with a percentage of the population having been infected weaker than expected, according to researchers with british and Swedish.

Since the beginning of the pandemic coronavirus, most of the estimates argued that around 60 % of the population will acquire immunity against the COVID-19 to brake his momentum. However, according to a study published this week in the journal Science, this proportion could be approximately 43 % when this immunity is acquired in a natural way.

Recall that herd immunity is achieved when a sufficient proportion of the population develops antibodies that protect against a second infection by a particular virus. This virus worth it then to infect new people and the progression is slowed or even stopped.


This immunity may be acquired naturally by contracting the virus or by receiving a vaccine. It must provide effective protection and durable enough, which is not always the case.

In the case of the coronavirus SARS-CoV-2, which causes the disease COVID-19, the concept of immunity of mass must be approached with caution because science has not yet established the degree of protection offered by a first infection, or how long it lasts.

Scientists affiliated to the universities of Stockholm in Sweden and Nottingham in the United Kingdom, which have used a mathematical model to support their conclusions, explained that the social behaviors that differ from one person to another.

The more people are socially active, the more likely they are of being infected and of infecting other persons, they point out.

Taking into account of this variable and of the distribution of age groups in the society, herd immunity, acquired naturally, would be reached with a percentage of the population lower than thought – as long as the COVID-19 effectively generates a satisfactory immune response.

New approach

“The figure of 60 % assumes that each individual in the population is also likely to be vaccinated, and therefore immune. However, this is not the case if immunity is the result of the spread of the disease in a population composed of individuals with many different behaviors, ” explains a statement released by the University of Nottingham.

“By adopting this new mathematical approach to estimate the level of herd immunity to be achieved, we have found that it could potentially be reduced to 43 %,” said one of the authors, Frank Ball.

This estimate should, however, be interpreted with caution, ” as an illustration rather than an exact value “, warn the researchers.

— With the collaboration of the QMI Agency

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