Re-immunity may slow the spread of COVID-19 in some parts of the U.S., scientists say, because a study finds that a population-wide infection rate of about 40 percent may be enough to achieve this form of community protection against the disease.
The U.S. has confirmed more than 5.4 million cases of COVID-19 – although the true figure may be significantly higher – and recorded more than 160,000 deaths, according to the Johns Hopkins Coronavirus Resource Center.
However, humans can develop at least some form of immunity after infection, which means the number of individuals vulnerable to the disease in severely affected areas – such as southern states that have recently seen large spikes in infections – is declining, according to pandemic analyst Trevor Bedford of the University of Washington.
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“I wanted to discuss the extent to which the population’s immunity can contribute to COVID – 19 restriction in Florida, Arizona and Texas, where recent surges have resulted in substantial epidemics,” Bedford wrote in a series of tweets. “After increasing dramatically in June and July, daily business counts in Florida, Arizona and Texas began to decline.”
“I believe the substantial epidemics in Arizona, Florida and Texas will release enough immunity to help keep COVID-19 under control,” he said.
Taking Florida as an example, Bedford estimated that about 20 percent of the state’s population – about four million people – had COVID-19, although it could “easily” be 10 percent.
“Assuming that a large majority of infections left enough immunity to be protected (which I believe to be the case) population population immunity will have a 20 percent real impact if social behavior Rt has already decreased to around 1.2,” Bedford said.
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Rt is the actual transmission rate of the virus at a given moment. If there is more than one, the number of cases will continue. If it is lower than one, the number of cases will eventually peter out to zero.
“Even 10 percent immunity starts to make a difference when Rt is about 1.2,” Bedford said.
Scientists have suggested several estimates for when link immunity against the new coronavirus can be achieved in a given population, with estimates ranging from as low as 10 percent infected to as high as 80. Many believe that link immunity can only be achieved against an unacceptable cost of living.
For a study published on Friday in the journal Science, researchers from the University of Stockholm in Sweden and the University of Nottingham in the United Kingdom decided to investigate the problem of herd immunity, and found that it could be achieved at a population-time infection rate of about 40 percent – significantly lower than many previous ones. rumors.
In their paper, the researchers focused on the fact that human populations are far from homogeneous in terms of their age and activity level. That they created a mathematical model to show how these differences can affect the spread of the disease.
They found that by introducing these differences into population models for the spread of the virus, the threshold for herd immunity could be reduced to about 40 percent, because “the proportion of infected individuals in groups with the highest contacts is greater than that in groups with low contacts. “
“This shift is because transmission and immunity are concentrated among the most active members of a population, who are often younger and less vulnerable,” the researchers wrote. “If non-pharmaceutical interventions are very severe, no herd immunity is achieved, and infections will recur if they are relieved too quickly.”
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Despite Bedford’s estimates of increasing herd immunity in Florida, Arizona and Texas, the scientist warned that the level of protection he found in those states was “incompatible” with a return to the kind of life people lived before the pandemic.
Furthermore, Bedford said that the costs of achieving this level of immunity have been “substantial” so far and continue to increase.
“I strongly believe that the ‘herd immunity’ strategy for dealing with COVID-19 is far too costly in terms of health consequences. But it seems that the strategy may be inadvertently followed in parts of the US. We have a vaccine needed to achieve population immunity in a way that does not kill people.
It is still not clear to what extent any compromised immunity to the virus that causes COVID-19 – known as SARS-CoV-2 – slows its spread. However, it is clear that some states that saw significant spikes in new infections in June and July, such as Florida, are now beginning to see a decrease in new daily cases.
Youyang Gu, a computer scientist whose pandemic models are used by the Centers for Disease Control and Prevention, believes that social distance measures and behavioral changes may be responsible for some of the cases, while increasing immunity may also play a role.
“Immunity can play a significant part in declining regions,” Gu said. MIT Technology Review. “I do not think there will be another spike” of infections in southern states, “he said.
Indeed, Gu estimates that around 35 million Americans are infected with SARS-CoV-2, which is equivalent to about 10 percent of the population and much higher than the official number.
“Clearly, as sensitivity decreases, disease spread decreases. No one can say otherwise,” said Tom Britton, an author of the latter Science study from Stockholm University told the Technology Review. “The question is, to what extent is the effect due to interventions or because of immunity? In regions with very large outbreaks – New York, Milan, Madrid and London – I am convinced that it is a combination.”
