Delta variant: due to its dangerousness, collective immunity would only be achieved after having exceeded 80% of the vaccinated population

The spread of the Delta variant of the coronavirus has caused the herd immunity threshold to far exceed 80% and potentially approach 90%, according to a briefing from Infectious Disease Society of America held Tuesday in the United States.

This represents a “much higher” bar than previous estimates of the 60% to 70%, because Delta is twice as transmissible, He said Richard Franco, assistant professor at the University of Alabama at Birmingham. “It is becoming increasingly clear that this is a very dangerous virus, much more dangerous than the originalsaid Franco.

Collective immunity is based on the idea that when a certain percentage of the population has been vaccinated against the virus or acquires immunity against a previous infection, It helps protect the general population and reduce transmission.

According to CDC data, nearly 60% of Americans have received at least one dose of the coronavirus vaccine, and about 50% were fully vaccinated, which represents about 165 million people. For their part, some 35 million people in the United States have tested positive for the virus during the pandemic.

In this sense, this Tuesday, the President of the United States, Joe Biden, reiterated a concept that has been repeated for several weeks: “We have a pandemic of unvaccinated.”

Collective immunity (also called collective immunity or collective immunity) is the indirect protection against an infectious disease obtained when a population becomes immune. Comprehensive COVID-19 vaccination aims to reduce severe cases and deaths, and achieve collective immunity to reduce the circulation of the coronavirus and control the pandemic.

More than a year and a half after the start of the pandemic, Only 14.7% of humanity has already accessed the full COVID-19 vaccination regimen. This limitation of access to vaccines and the appearance of variants such as Delta will in the short term prevent collective immunity from being obtained, according to experts in epidemiology and virology.

Last year, it was estimated that 70% of the world’s population needed to be vaccinated to gain herd immunity. However, the emergence of variants of concern has led researchers to consider that a higher proportion of fully immunized people will be needed. After delays in vaccine application (in low-income countries, only 1.1% accepted at least one dose), the coronavirus continued to spread around the world and the chances of different variants emerged. increases.

The Delta variant of the coronavirus has already been detected in 132 countries in 5 of the six regions of the world. It mainly progresses in people who have not yet been vaccinated. This combination of factors will delay the scope of collective immunity. Andrew Noymer, epidemiologist at the University of California, Irvine, United States, told the magazine British medical journal that vaccines reduce the risk of hospitalization for COVID-19 even if people are given the Delta variant.

“If the vaccinated can become infected and, as we believe from other studies, potentially spread the coronavirus, then herd immunity becomes more of a mirage than an oasis”said Doctor Noymer.

The percentage of people who must be immunized to gain herd immunity varies for each disease. For example, to obtain collective immunity against measles about 95% of the population needs to be vaccinated. The remaining 5% will be protected because measles will not spread among those vaccinated. In the case of polio, the threshold is around 80%.

In the case of COVID-19, it is not yet clear exactly what the new collective immunity number could be, but there are already experts who place it around 90%. This proportion would require including the infant population in access to vaccines. The concept of collective immunity is based on the fact that when a sufficient number of the population is immunized, the virus does not have the capacity to spread.

In dialogue with InfobaeRodrigo Quiroga, researcher at Conicet and the National University of Cordoba, estimated that “herd immunity will be difficult to achieve in the near future if the infant population is not vaccinated. Taking into account the extremely high contagiousness of the Delta variant, it would be necessary to vaccinate 95% of the population to reach it. In addition, it may be necessary to take other precautions such as avoiding mass meetings ”.

According to a report from the US Center for Disease Control, vsEach person can infect nine more if they are infected with the Delta variant. This means that the contagion is between three and four times greater than what was initially calculated. As a result, the percentage of the vaccinated population needed to achieve herd immunity is changed. If at the beginning we spoke of a 70%, now they consider that the threshold has been exceeded, and those who manage to specify it raise it around the 90% or more.

According to Spanish epidemiologist Javier del Águila, since it is a respiratory virus with such high transmissibility, coverage rates close to 95% would be needed to achieve herd immunity. “It is very difficult, even in countries like Spain, where reluctance to vaccinate is very low.», Warned the expert.

At the same time, José Jiménez, researcher in the Department of Infectious Diseases at King’s College London, estimated that herd immunity due to vaccination might involve different percentages in different countries. “The best message we can give is to vaccinate as much as possible without setting any percentage as a target,” he said.

Another possibility is – according to Miguel Hernán, professor of epidemiology at Harvard University, United States – that the coronavirus becomes endemic, as it happens with other pathogens. like colds. “Maybe in their day they were a pandemic and today there is no epidemiological surveillance of them because it is not necessary,” he said.

To reach percentages of 95% like that described by Del Águila, it would be essential to also vaccinate the children. However, not all countries have yet agreed to immunize the child population. The Joint Committee on Immunization and Immunization (JCVI) which advises the UK government clarified in July that “the health benefits for this population are low and the benefits for the general population are very uncertain”. Experts felt that “the health benefits of universal immunization in children and young people under 18 do not outweigh the potential risks.”

Differences were raised between developed and developing countries. Some, like Israel, which started out as a world leader, have been stuck for weeks at around 60% of people on the full immunization schedule. The United States has already vaccinated 60.4% of the population over 18 with the full regimen. On the other hand, for developing countries, vaccination lags behind and collective immunity is a pipe dream.

“As the virus circulates in the world, it will have more ability to mutate, and the more it does, the more likely it will be to escape vaccines,” Del Águila pointed out. As it continues to circulate, the chances of other worrisome variants appearing, and this situation could generate new epidemics in countries with high vaccination rates.

WHO pandemic ambassadors alerted world political leaders a few days ago. They propose that at least 10% of the population of each country be vaccinated in September, and a “push until December” to vaccinate 40% by the end of 2021. “Reaching the September target means an additional 250 million people in low- and middle-income countries need to be immunized in just four months, prioritizing all health workers and groups most at risk to save lives“, They argued.

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