As the COVID-19 pandemic has dragged on into its fourth month, public health officials are not optimistic that populations will be able to build up a functioning “herd immunity” to the disease before a vaccine is developed — something that could still be several months away.
The idea of herd immunity is based on the concept that, if a large enough percentage of a population becomes immune to a certain disease, it will break the chain of transmission, make the disease less likely to spread and, at a certain point, the immunity of the group will protect even those who aren’t immune.
Earlier this month, Alabama Senate Pro Tem Del Marsh, R-Anniston, injected the concept into statewide media coverage of COVID-19 when he told a reporter from Huntsville he wanted to see more people contracting the disease because “we start reaching immunity if more people have it and get through it.”
He later clarified those statements and emphasized that he didn’t want to see anyone develop serious complications or die from the disease. But absent a widely distributed vaccine, top health officials don’t believe there’s evidence to suggest Alabama’s population could achieve herd immunity to COVID-19.
Even if it could, some worry that the human cost might be too high.
Dr. Karen Landers, assistant state health officer with the Alabama Department of Public Health, told Lagniappe not all communicable disease achieves herd immunity, and for others, it requires a majority of a population to be exposed to the infection. As an example, she said roughly 94 percent of a population has to be immune in order to maintain herd immunity to measles.
“With COVID-19, we really do not know what that threshold is. We think 70 percent or more would have to have been infected to achieve it, but the biggest challenge with COVID-19 is that we don’t even know how long immunity from natural infection lasts,” Landers said. “So, 70 percent might not even confer lasting immunity, and that’s still a whole lot of people getting sick. We also have to consider people who have underlying complications and people who could even die from the disease.”
If 70 percent of Alabama’s 4.9 million population became infected with COVID-19, that would be 3,430,000 confirmed cases statewide. Apply the 1.8 percent mortality rate seen in the state’s 69,075 cases so far, and there could be as many as 60,000 deaths before 70 percent of the state contracts the disease.
However, as Landers mentioned, no one knows for sure what the herd immunity threshold for COVID-19 might be and some isolated outbreaks have suggested it could be much lower. One recent study at Oxford University suggested 20 percent of a population being exposed could be enough to prevent a widespread resurgence of COVID-19 based on the idea that some people may already have some degree of resistance to the virus from exposure to seasonal coronaviruses like the common cold.
It’s important to note the Oxford study, which was released July 16, hasn’t been peer-reviewed yet, and most local health officials believe relying on herd immunity without an effective vaccine isn’t a viable strategy.
Dr. Rendi Murphre, an epidemiologist with the Mobile County Health Department, said that there are still too many unknowns about the disease that scientists have only been studying a few months — including how long someone’s immunity to COVID-19 lasts after they’ve become naturally infected.
“Historically, we have not been able to control things like measles and other preventable diseases without a good staff of vaccines that are taken by a large portion of the population,” Murphree said. “It is unlikely that just letting a disease burn along would provide herd immunity any time soon.”
Given the unknowns, Landers said the best the epidemiologists and medical professionals can do at the moment is compare COVID-19 and the novel coronavirus that causes it to viruses that are similar. For years, Landers said the best way to mitigate the spread of viruses that cause things like the common cold and influenza has been through targeted vaccines and individual efforts to limit transmission.
“When we’re looking at it from this perspective, we have to say right now that it’s a good idea for everybody to try to prevent contracting or spreading COVID-19,” Landers said. “It’s important people take all the measures to protect themselves and also other vulnerable members of the population.”
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