Ask Dr. Halverson: Do some people have pre-existing immune protection against coronavirus?

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By Dr. Jim Halverson
We’re now more than seven months into the pandemic that has affected the lives of most of Earth’s inhabitants. While it is true that the scientific community has learned many things about the SARS-CoV-2 virus and the disease that it causes, COVID-19, there are also many gaps in our understanding.
Dr. Sanjay Gupta, chief medical correspondent for CNN, in an Aug. 2 article, addresses one of the biggest and most intriguing questions: Why do some people get very sick and even die from their illness, while other people with similar risk show no symptoms and may not know they have been infected at all?
We know some of the factors that put people at higher risk of having a severe, even fatal, course of the disease are being over 60; obesity; having one or more chronic diseases such as diabetes, cardiovascular disease, kidney or lung disease, and cancer; and being a person of color — Black African American, Latino or Native American.
Could the opposite also be true? Might some people have pre-existing immune factors that lessen their risk?
A recently published article in the journal Nature Reviews Immunology put forth an exciting possibility: Perhaps as many as 50% of the population in certain areas of the world may have immune cells that are able to recognize parts of the SARS-Cov-2 virus. Those immune cells could possibly give them a head start in fighting off COVID-19. 


 Alessandro Sette, from the Center for Infectious Disease and Vaccine Research at La Jolla Institute for Immunology, states in that article that about half the people they tested in the San Diego area had T-cells that were reactive against the SARS-CoV-2 virus. None of those people had ever been exposed to the virus and the blood samples were drawn and stored in 2018.
Our immune system includes two types of white blood cells —T cell lymphocytes and B cell lymphocytes. B cells have a unique antibody that sits on its surface and can bind to a unique antigen on the invading pathogen (on the SARS-Coronavirus-2, this is called the spike protein). When the B cell antibody binds to the antigen, it activates the B cell, which then makes multiple copies of itself and lots more of the unique antibodies that neutralize the coronavirus and make it unable to enter a human cell. Individuals previously infected by the SARS-Coronavirus-2 continue to carry these antibodies after the infection is gone. 
Unfortunately, a few recent studies have found that antibodies to this particular coronavirus can fade away pretty quickly, especially in people who have had mild cases of COVID-19. This has worried many researchers. Because the antibody response appears to fade quickly, the scientific community is not sure how long a person who has been infected with this virus will stay protected from a new infection. This is also worrisome since we are relying on vaccines to trigger an antibody response to help protect us, and we want that to last a long time.
Fortunately, we also have T-cells. There are three main types of T-cells — helper T-cells that enhance our immune response to a pathogen; killer T-cells that can kill human cells that have been infected with the virus, thus preventing further viral replication; and memory T-cells that help our body remember a virus if it comes back as a future infection. 
It’s the memory T-cells that Sette and his co-author, Shane Crotty, discovered, quite by accident, in the blood of people collected several years before this pandemic began. They are not the only ones to have found this. These findings have now been confirmed in different continents, in different labs, and with different techniques, which is one of the requirements for scientific validation. They speculate that this T-cell recognition of parts of the SARS-CoV-2 virus may come in part from past exposure to one of the four known circulating coronaviruses that cause the common cold in millions of people every year.
Many questions remain to be answered, including whether this recognition to parts of the SARS-Cov-2  by T-cells helps lessen infection. “It’s reasonable to speculate that they may be helpful,” said Crotty. “It’s not that we think they would completely protect against any infection at all, but if you already have some T-cells around, they can fight the virus faster. It is plausible that instead of ending up in the hospital, you just end up with a bad cold.”
Most current vaccines being developed are designed to produce protective antibodies. If a T-cell vaccine can be developed against SARS-COV-2 (much as ones have been developed and are being used against certain cancers, like melanoma), it could improve survival of those who did get the disease. In other words, those vaccines would not protect against infection, but they might make infections so asymptomatic that you would not notice it in yourself and, in fact, you would never have enough virus in your body to transmit it to somebody else.
In addition, if a percentage of the population currently has some degree of T-cell immunity, they could count toward the number of people who need to be immune to get the epidemic wave to die out. For the SARS-COV-2 virus this is estimated to be approximately 70% of the population.
This discovery is one of many that have been made due to the dedicated and tireless work of scientists and physicians around the world. Thanks to their efforts, we are moving ever closer to achieving adequate protection from this virus.
Stay hopeful. Do all you can to lower the risk of this infection to yourself and to others. Ultimately, our medical and scientific community working in the United States and in many countries of the world will have treatments and one or more vaccines that can protect all of us. 
Stay positive, stay committed, stay safe and stay well.

— Dr. Jim Halverson is a longtime Ojai physician who writes a weekly column about COVID-19 for the Ojai Valley News.

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