Coronavirus: How long does convalescent plasma immunity last? 2:23

(CNN Spanish) – In the five months that have passed since we first learned about the coronavirus, we have read the term de group immunity ’or de herd immunity’ as a strategy to end the pandemic on several occasions.

UK Prime Minister Boris Johnson suggested in March that “herd immunity” is one of his strategies to control the outbreak, and after harsh criticism, the British government gave up on such plans.

In this episode, Dr. Elmer Huerta explains what this concept is about and analyzes some studies carried out in various European countries.

You can listen to this episode on Spotify or your favorite podcast platform or read the transcript below.

Hello, I am Dr. Elmer Huerta and this is your daily dose of information about the new coronavirus, information that we hope will be useful to take care of your health and that of your family. Today we will see what the group’s immunity consists of as a strategy to end the pandemic, and how close or far we are from it.

Group immunity, also called group or herd protection, is defined as the phenomenon in which the spread of an infectious disease, from person to person, is made very difficult because the majority of the population has already become immune to said infectious disease. This is generally accomplished by vaccination.

Take, for example, the case of measles, a highly contagious disease. If 90 or 95% of the population were vaccinated and a person appears with the virus, they would have no one to infect, because –without redundancy– 95% of the population would be protected by the vaccine.

Conversely, if less than 90% of the population is protected by the vaccine and a measles case occurs, the virus would be more likely to infect another person and cause an outbreak of the disease.

Due to pressure from anti-vaccine groups, this unfortunate situation has been repeated in several countries around the world, where measles outbreaks have arisen because less than 95% of the population had been vaccinated.

The term group immunity has been extended to the present pandemic, and it has been calculated that if 60 to 70% of the world’s population were infected, we would have achieved group immunity and the pandemic could disappear, according to the Center for Disease Research. Infectious and Political University of Minnesota.

What has been more difficult to calculate is the time it would take for 60 to 70% of a given population to become infected and therefore group immunity to develop.

Recent serology studies, which contemplate random blood tests in representative groups of the population, give us, however, an idea of ​​how difficult it could be to reach that level of infection in a community.

For example, a study carried out in Spain by the Carlos III Health Institute, between April 27 and May 11 in a sample of 60,000 people, reveals that only 5% of the population was infected with covid-19.

Spain was one of the countries hardest hit by the pandemic, which has left almost 27,000 deaths to date. Many observers, proponents of group immunity, expected a higher number of infections in the population.

Madrid, for example, one of the most affected cities, only showed a prevalence of 11.3%.

Similarly, in France, a country also severely affected by the pandemic, a study by the Pasteur Institute calculated that by May 11 only 4.4% of the general population was infected with the coronavirus, having found that in areas with the highest number of cases, such as Paris, only 9 to 10% were infected.

The same findings have been made in England. After being heavily affected by covid-19, only 4% of Britons are infected, and in London the figure is around 10%.

However, Oxford University had projected that between 36% and 68% of the country’s population would be infected by March 19.

Finally, a natural experiment – conducted in Sweden – reveals that achieving group immunity may not be so easy. Unlike its Nordic neighbors, Sweden decided not to institute strict confinement in society, keeping most bars, restaurants, schools, and retail stores open.

His expectation was to achieve mass immunity by having his young and risk-free population become infected and develop immunity against the virus.

Sadly, a recent study revealed that only 7.3% of Stockholm’s population has been exposed to the virus, and authorities expected it to be 25%.

The price Sweden has had to pay for this strategy has been observed by its own population: Swedes have 7 to 9 times more cases per 100,000 residents than their neighbors Finland and Norway respectively, who did implement quarantine measures.

Without a doubt, the behavior of the new coronavirus is still a mystery to scientists. The fact is that, at least from the studies described, it will take a long time for group immunity to be achieved from 60 to 70% of the world population.

That means that the hopes of controlling this pandemic, in a more reasonable time, lie in finding a medicine or a vaccine that is effective and accessible to the majority of the population.

Send me your questions on Twitter, we will try to answer them in our next episodes. You can find me at @DrHuerta.

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And to get updated information, you can always go to Thanks for your attention.

If you have any questions, you can send them to Dr. Elmer Huerta on Twitter. You can also go to for all the episodes of our podcast “Coronavirus: Reality vs. fiction”.