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U.S. immunity not high enough to contain COVID-19

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Although a vaccine against the SARS-CoV-2 virus has been widely available for months and millions of Americans have natural immunity, a new report suggests that overall immunity at the population level in the United States might still be too weak to contain the virus.

The new report, published in the Annals of Internal Medicine, is based on published statistics and epidemiological simulation modeling. He warns that at least since this summer, the United States has not been able to let its guard down.

Corresponding author Alison P. Galvani, PhD, of the Yale School of Public Health, and colleagues noted that as of the end of July, the country had reported 34 million cases of COVID-19, and about 6 adult Americans out of 10 had been fully vaccinated.1 At the same time, they noted that the Delta variant of SARS-CoV-2 was spreading rapidly and that many Americans were ignoring public health recommendations like masking and social distancing.

“Lack of adherence to non-pharmaceutical interventions before achieving sufficient population immunity carries a significant risk for another wave of COVID-19 cases and deaths,” they wrote.

Yet Galvani and colleagues have also suggested that the official tally of people immunized due to a previous infection may not be accurate, in part due to the presence of asymptomatic cases, in which individuals may not have been tested. for the virus because they never experienced symptoms.

Given the uncertainty about the actual level of immunity in the population, investigators embarked on the use of statistical modeling and simulation, as well as publicly reported COVID-19 death data to extrapolate the estimates. stratified by age of actual immunity. The main outcome of the study was the immunity of the population, a measure that takes into account the impact of vaccination as well as those who would have immunity based on previous infections.

This analysis suggested that as of July 15, 2021, approximately 114.9 million Americans had been infected with SARS-CoV-2, leading to an overall population average immunity of 62.0%. Based on an age cohort, estimates ranged from 77.2% among Americans 65 and older to just 17.9% of children under 12.

Galvani and his colleagues said these immunity levels may not be enough to fight new variants of the disease.

“Variants of SARS-CoV-2 with higher transmissibility, such as the Delta variant, will inevitably increase levels of naturally acquired immunity, but at the cost of potentially more serious health problems,” they noted.

Raising vaccination rates would help speed up the immunity of the population, they noted, although the vaccine is not equally effective against all variants of the virus.

“Our study highlights the need to accelerate vaccination to prevent further waves of COVID-19 and the development of new variants and to shorten the time taken to control the pandemic in the United States,” the authors concluded.

Galvani and colleagues also reported significant regional variation in immunity at the population level.

“For example, many states in the northeast have achieved high vaccine coverage and low infection rates, while parts of the south and midwest have relatively low immunization rates and high infection rates,” they wrote.

With such variation in immune status and the potential for newer and more contagious variants, the authors said that non-pharmaceutical interventions such as masking and proactive testing should continue “at least until immunity of. the population is high enough to contain the pandemic “.

The references

1. Moghadas SM, Sah P, Shoukat A, Meyers LA, Galvani AP. Population immunity against COVID-19 in the United States [published online ahead of print, 2021 Sep 14]. Ann Med Intern. 2021; M21-2721. doi: 10.7326 / M21-2721

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