Herd immunity may require vaccination of 90% of the population

Which portion of the population must acquire resistance to the new coronavirus for a country to reach herd immunity, making transmission of Sars-CoV-2 more difficult? At the beginning of the pandemic, it was estimated that between 60% and 70% of citizens were immunized, but this estimate has been increasing in recent months.

In an interview with The New York Times on Thursday (24), immunologist Anthony S. Fauci, one of the leading specialists in infectious diseases in the United States, said that it may be necessary to vaccinate about 90% of the population to achieve collective immunity and, thus, society will return to normal life.

In the early months of the health crisis, Fauci was one of the scientists who predicted lower immunization rates. However, the American government adviser has gradually increased his estimates: in November, they went from 70% to 75%, but in early December they increased to more than 80%.

Anthony Fauci next to Donald Trump.Source: Wikimedia Commons

One of the reasons that made the specialist change his mind was the discovery of new strains of the causative agent of covid-19, identified in the United Kingdom and South Africa, among other places, showing a greater transmission capacity. The large number of Americans stating that they do not intend to be vaccinated (around 20%), pointed out by recent research, has also contributed to this.

Measles level

The new herd immunity index to halt the transmission of covid-19 as pointed out by the immunologist (who advises Donald Trump’s actions in response to the pandemic) is approximately 90%. This is almost comparable to that needed to eradicate measles, one of the most contagious diseases in the world.

Caused by a virus that can stay in the air for hours, in addition to floating through any opening and infecting people in other locations, measles only stops spreading when 95% or more of people are immunized, according to dormitory outbreak studies. students and military barracks.

Vaccination is one of the ways to achieve collective immunity.Vaccination is one of the ways to achieve collective immunity.Source: Pixabay

Despite the increase in the collective immunity range for covid-19, Fauci guaranteed that the new coronavirus does not have the same transmission rate as the measles virus. “I would bet my house that covid-19 is not as contagious as measles,” he said.

It is important to note that this population’s immunity can be achieved both through an efficient vaccination program and through direct contact with the virus. In the latter case, the infection leads to the development of antibodies, but it can result in a large number of deaths.

What other experts say

Other experts agree with Fauci’s new estimates of the collective immunity rate, but point out that any prediction about Sars-CoV-2 is only “guesswork”, due to the short time of study of the disease.

For the epidemiologist Marc Lipsitch, from the Harvard School of Public Health, several factors can influence this type of calculation, for example, differently from the measurement made in real herds, in which there is total control over the confined animals. He also says he believes it is not necessary to reset transmission to return to normal and mentioned other diseases.

The World Health Organization (WHO) director of immunization, Katherine O’Brien, refused to make estimates, in addition to commenting that the collective immunity index varies from place to place. “We should say that we just don’t know. And it will not be a worldwide or even a national number. It will depend on the community where you live, ”she said.

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