Is herd immunity from COVID-19 possible?

July 25, 2020 — Even with 88% of Americans wearing masks in public, people being forced by government to not work, government mandates to wear a mask in public, and no large crowd events are permitted by the government, cases of COVID-19 continue to rise across the nation. What government is doing is not stopping the spread of COVID-19. An unknown number of Americans are staying home and not interacting with others in person, but via Zoom, Google Meet, and other socially distanced methods of communicating. Businesses are sanitizing like never before to help stop the spread of the virus, but numbers continue to increase. Is any of this effective at stopping or curbing COVID-19 infection rates?

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We also know that other countries use masks while living in a very sanitized world, and yet their infection rates for COVID-19 are still high. One example is Hong Kong where there is a 97% compliance rate for wearing masks in public or face a $5,000HK fine, yet their numbers for infection remain high and are experiencing a third wave of infections.

Is what we have been doing prolonging the existence of the virus while devastating our economy? Is there a better option to ending this sooner rather than later? These are all questions many of us are asking, which brings us to “herd immunity.” We define herd immunity as a level of population immunity such that disease spreading will decline and stop even after we have relaxed all preventive measures. We base most herd immunity models on vaccination numbers, but what about situations, like with COVID-19 when there is no vaccination available?

Science Magazine tried to tackle the issue and found that “We estimate that if R0 = 2.5 in an age-structured community with mixing rates fitted to social activity then the disease-induced herd immunity level can be around 43%, which is substantially less than the classical herd immunity level of 60% obtained through homogeneous immunization of the population.” As an example, Polio needed about 80% of the population to be immune before it was mostly eradicated. It is unfortunate the science on novel COVID-19 differs so much and there is so little good science available. As even the Science Magazine mathematical model discovered and admitted, “Our estimates should be interpreted as an illustration of how population heterogeneity affects herd immunity, rather than an exact value or even a best estimate.”

Plot of the overall fraction infected over time for the age and activity structured community with R0 = 2.5, for four different preventive levels inserted March 15 (day 30) and lifted June 30 (day 135). The blue, red, yellow and purple curves correspond to no, light, moderate, and severe preventive measures, respectively.

We can obtain one piece of insight regarding herd immunity in the U.S. for COVID-19/SARS-CoV-2, as it may lie in the close genetic material it has with SARS-CoV. One getting SARS-CoV will have effective antibodies in their system for two to three years, while antibodies peak two to four months after infection.

One thing we know through the expansion of the number of tests being done in America is that a great number more people have the COVID-19 than previously thought. Some people feel we may be close to herd immunity already, while others say such a number (around 200 million) of infections are months away.

Karolinska Institutet and Karolinska University Hospital went a step beyond antibody testing and delved in to how t-cells were reacting to the virus. “One interesting observation was that it wasn’t just individuals with verified COVID-19 who showed T-cell immunity but also many of their exposed asymptomatic family members,” says consultant Soo Aleman. “Moreover, roughly 30 percent of the blood donors who’d given blood in May 2020 had COVID-19-specific T cells, a figure that’s much higher than previous antibody tests have shown.” The conclusion of their study found that public immunity is probably higher than antibody tests suggest.

As this point, we do not know enough about COVID-19 due to not having enough time and enough quality studies to base any concrete facts regarding whether herd immunity would work for COVID-19. And if herd immunity was effective, how many people would die during the process is an unknown, at least until a safe vaccine was readily available for those willing to take it.



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  1. Science on efficacy of face masks for viruses is mixed – The Palm Beach Examiner
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