There has been a lot of discussion on herd immunity to COVID-19 lately as new studies suggest that people’s immune system has the ability to recognize the virus, explaining why certain individuals have only mild symptoms or none at all.
Herd immunity happens when a large number of people are immune to a disease—either from prior infection or vaccination—which acts to stop or slow down the spread, thus protecting the entire community, including those who have not had the illness.
Estimates for percentages needed for herd immunity has mainly focused on the role of antibodies of those who have recovered from COVID-19, although scientists are still unsure how long the antibodies protect against reinfection.
Studies are now also beginning to consider the contribution of T-cells to herd immunity for COVID-19.
T-Cell Immunity for COVID-19
Director of the National Institutes of Health Dr. Francis Collins said in his blog post that studies on the immune response to SARS-CoV-2, the virus that causes the COVID-19 disease, have concentrated mostly on the body’s production of antibodies to determine if we will have immunity against the disease.
“But, in fact, immune cells known as memory T-cells also play an important role in the ability of our immune system to protect us against many viral infections, including—it now appears—COVID-19,” Collins said.
T-cells (along with B-cells) are a type of white blood cell that plays an essential part in the adaptive immune system by assisting the body in destroying and remembering antigens—foreign substances that invade the body. Although T-cells are produced in the bone marrow, they travel to the thymus, a small organ between the lungs directly behind the sternum in the chest, where they will mature into different types of T-cells with specific roles.
As people get older, the thymus shrinks, affecting the production and functionality of T-cells, and so adults 60 and older become more susceptible to infections. The elderly population has been the most affected in the pandemic, where at least 45 percent “of all COVID deaths are coming from 0.62 percent of the population—those in nursing homes and assisted living facilities,” Dr. Tom Reed, a double board-certified medical and surgical specialist, told a Facebook discussion hosted by Texas state Sen. Bob Hall.
A study published in Nature that Collins cites in his blog suggests that the immune system’s T-cells may offer protection against COVID-19 by “remembering past encounters with other human coronaviruses,” explaining why certain people can fight off the illness or experience only mild symptoms.
There are six coronaviruses besides SARS-CoV-2 that infect humans—four of them cause the common cold, while two caused the 2003 Severe Acute Respiratory Syndrome (SARS) outbreak and the 2012 Middle East Respiratory Syndrome (MERS) outbreak. These coronaviruses produced both memory T-cells and antibodies in infected individuals, but it was the memory T-cells that continued to confer immunity for over a decade, according to the study.
Multiple studies have been published since the Nature study confirming similar results.
The latest one to be published in Cell (pdf) shows a more promising role for T-cells in developing herd immunity against COVID-19.
Researchers found that “donors exhibited robust memory T-cell responses months after infection, even in the absence of detectable circulating antibodies specific for SARS-CoV-2, indicating a previously unanticipated degree of population-level immunity against COVID-19.”
Dr. Scott Atlas, President Donald Trump’s new advisor on the pandemic, said last month that emerging data showed that people who didn’t get infected have been found to have COVID-19 immunity. “This is probably due to this T-cell immunity, which is present, and is now shown to last for years,” he said.
Atlas, speaking during an appearance on Fox News, pointed to research from Singapore and from Sweden’s Karolinska Institute. Researchers from the institute stated that many people with mild or asymptomatic cases of COVID-19 demonstrate T-cell-mediated immunity to SARS-CoV-2.
Achieving Herd Immunity
It is generally thought that an estimated 60 to 70 percent of the population needs to become infected by SARS-CoV-2 before herd immunity is achieved. “However, several recent studies have suggested that depending on specific population factors (population density, propensity for travel, susceptibility, etc.), this number may be considerably lower in some sub-populations in particular places around the country,” Dr. Michael Devine, dual-board certified internist and geriatrician and co-founder of Devine Concierge Medicine, told The Epoch Times in an email.
But when asked if some states are already seeing herd immunity, Devine says he doesn’t believe that is the case just yet.
“In every measure we do have at present, the perceived proportion of the population who is believed to have acquired (by having been infected directly) or innate (naturally occurring or genetically predisposed) immunity falls vastly short of any model prediction that would infer herd immunity,” Devine said.
“The reduction in cases currently being enjoyed in some states is the byproduct of healthy population habits—social distancing, utilization of face coverings when in public, and maintaining good hand hygiene.”
Devine also said that limiting travel, the warmer weather, and people “spending more time outdoors, rather than being cooped up in close quarters” may be contributing to the lessening prevalence of the virus.
In a live Instagram session on Aug. 13, Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said that sunlight kills the virus. “That’s one of the reasons why outside, in the sun, when you are interacting that, that is much better than being inside.”
Another important reason for people to be outdoors is to allow their skin to be exposed to direct sunlight for 15-30 minutes without being sunburnt, to activate the production of vitamin D—an important hormone that helps to fight off infections and regulate the immune system. Studies have found that vitamin D deficiency is associated with increased COVID-19 infection risk.
A study by the Georgetown University Medical Center in 2016 found that sunlight, specifically low-level blue light, also “energizes T cells that play a central role in human immunity” by making them move faster.
“T cells, whether they are helper or killer, need to move to do their work, which is to get to the site of an infection and orchestrate a response,” Gerard Ahern, PhD and lead researcher of the study said in a press release. “This study shows that sunlight directly activates key immune cells by increasing their movement.”
Areas of Possible Herd Immunity
States like Oregon, Washington, and Illinois—where large crowds of people are protesting and rioting frequently without social distancing and where some are not wearing masks—are not seeing a significant spike in new cases or deaths.
The Washington Department of Health tweeted on Aug. 14 that the state’s “COVID-19 cases are plateauing” even in King County where the riots continue to take place.
New report highlights COVID-19 cases are plateauing:
🔹 Reproductive # is hovering around one.
🔹 Seeing impacts of people using face coverings across the state.
🔹 Case counts are plateauing or declining in King and Yakima counties. https://t.co/qBTL6ePaWs
— WA Dept. of Health (@WADeptHealth) August 14, 2020
Oregon reported its lowest daily COVID-19 cases on Aug. 17 of 189 and no new deaths, bringing the number of total cases to 23,451 and a death toll of 388.
In Illinois, while daily cases began to rise again towards the end of June with the increasing number of tests given, the fatality rates had begun to significantly decline at the same time.
And in Ventura County in California, a church protesting Gov. Gavin Newsom’s lockdown mandate has been offering indoor services for its congregants (of up to several thousand people) for the past two months without any virus outbreaks, according to NTD. While the church does focus on properly sanitizing before and after services, Pastor Rob McCoy of Godspeak Calvary Chapel leaves it up to church members if they want to wear masks and physical distancing.
The pastor and his church members are facing legal consequences for attending an in-person church service after breaking a temporary restraining order to not hold indoor activities.
One possible explanation for lower deaths in these communities is that natural herd immunity has taken effect to some degree.
Zachary Steiber contributed to this story.