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When Will COVID Be Over? We Consult the Science Behind Disease Immunity

March 21, 2022
dr daniel skiest infectious diseases 250

Infectious disease experts know just how important it is to have a strong immune system when dealing with a new infectious agent like SARS CoV-2, the virus that causes COVID-19, which has led to many hospitalizations and deaths, since early 2020.

Despite the challenges of the past two years, Dr. Daniel Skiest, Infectious Disease Specialist at Baystate Health and Vice-Chair for Academic Affairs, Department of Medicine, and Professor of Medicine at UMass Chan Medical School-Baystate, says we are in a much better place now that there is an effective vaccine that helps protect people from becoming critically ill. He discussed how immunity works, and how our immune system can protect us when we are exposed to an invader like COVID-19.

How the Immune System Works

“When the body senses foreign substances (known as antigens)," Dr. Skiest says, “our immune system works to recognize the invader and remove it from the body.”

There are two types of immune responses – innate and adaptive,” Dr. Skiest says.

We are born with the innate immune system, though some people’s systems are compromised from birth. The innate immune system is the first response your body has when it becomes infected with a new pathogen (bacteria, virus, etc.). The immune system has several layers of protection against harmful invaders like COVID-19, from physical barriers (skin, nose, mucus, cough, trachea) to specific cells and chemicals.

“When our innate immune system detects an invader, it immediately goes into action,” he says. The innate immune response, which is the initial response, is nonspecific for each pathogen, and consists of certain types of white blood cells (neutrophils, macrophages, also known as phagocytes), which engulf pathogens and eliminating them from the body. The innate immune response represents a broad brush and is not as specific as the acquired immune response. If the innate immune response does not eliminate a pathogen, the adaptive immune response springs into action.

What About Antibodies?

There are three main types of blood cells, Dr. Skiest explains. There are red blood cells for carrying oxygen throughout the body, platelets for clotting, and white blood cells for fighting off infections. There are several types of white blood cells, including neutrophils, monocytes, basophils, eosinophils, and lymphocytes. There are two main types of lymphocytes known as B cells and T cells. Both B and T cells are important in the immune response.

B cells make antibodies that can attach to cells that are infected with a bacteria or a virus and help clear the infected cells from the body. T cells can either directly clear infected cells from the body, or indirectly help clear an infection from the body, by sending chemical signals to recruit other immune cells including B cells.

The Immune System’s Memory

He says B cells are triggered to make antibodies or immunoglobulins, which are proteins that attack a specific pathogen. Antibodies are very specific for each pathogen. Once the initial infection is cleared the B cells become dormant but if the pathogen comes back in the future the B cell can spring back into action and make more antibodies, even if it is month or years after the initial infection. The fact that the immune system has a “memory” forms the basis for the effectiveness of vaccines, like the COVID-19 vaccines. When the body is re-exposed to the same intruder or a mutated version of that intruder, the immune system will recognize and defend against it.

Natural Immunity vs. Vaccination

Throughout our lives, we develop immunity to specific pathogens. We develop immunity by being exposed to them either directly (by natural infection) or by receiving a vaccine that mimics natural infection and fools the body into making antibodies and T cells. When an invader has entered the body, antibodies recognize and remember.

We have seen SARS-CoV-2 mutate – starting out with what was known as Alpha, then Delta, and most recently the Omicron variant, Dr. Skiest says. The vaccine has been very effective in preventing serious illness and death in most cases. He says anyone who is eligible should receive all three doses of the vaccine.

“We have multiple studies that prove the vaccine is working,” he explains. “Even if an individual gets COVID-19 despite being vaccinated, the chances of getting very ill or dying are much less compared to those who are unvaccinated.” There is also evidence that natural immunity to COVID-19 weakens more quickly than immunity provided by vaccination.

So, why do patients get COVID-19 after prior infection or vaccination? Dr. Skiest says, “This is likely due to infection with new variants, which differ enough from prior variants due to the fact that the virus has mutated and so the vaccine doesn’t completely recognize each strain.” He says while the vaccine is protecting people from getting ill, the antibodies might not bind as well to the new variant.”

What is Herd Immunity?

Dr. Skiest says enough people must achieve immunity before you can reach what is known as herd immunity, which is the proportion of a population that has protection (immunity) from a pathogen. Herd immunity is a combination of those who achieved immunity by natural infection and by receiving the vaccine.

The number needed to achieve herd immunity in COVID-19 is not precisely known, but he believes that would have to be at least 85—90 percent. “If you reach herd immunity, the virus goes away because it can’t find hosts, it has nowhere to go. “

Should You Get Vaccinated After Having COVID-19?

Dr. Skiest says people can get vaccinated after having COVID-19, they just have to wait at least a month to let their natural immunity take hold, and he says some studies say vaccines will last four to six months, while others have indicated they might last as long as a year or more, similar to the flu vaccine.

“Again, this is all still so new,” he says. “We just can’t know everything about this, and we might never know everything. We are still learning about polio. Four years ago, some areas of the world were seeing new cases. We’ll learn as we go along about this brand new pathogen. But what I can say is this is unprecedented, how quickly we learned and it’s amazing how effective a vaccine that was developed so quickly is. Of course, we will learn as we go – that’s how science works. We totally expected that. This is faster than any other vaccine ever.”

We Still Have Much to Learn

Dr. Skiest says it isn’t a surprise that scientists and healthcare professionals still have much to learn about COVID-19.

“Of course, as we learn more about COVID-19, we need to modify our approach based on new information as it develops. This is how science works. I am actually quite impressed at how much we have learned and how fast we were able to develop an effective vaccine and effective treatments. I can’t think of any time in the past when we have moved so quickly in learning about a new pathogen, coming up with new treatments and disseminating the information.”

Stay Up to Date

As COVID-19 case numbers decrease in the United States, people have begun to loosen precautions and resume some sense of “normal.” Two main actions remain important during this time of relief: Get vaccinated/boosted and stay informed. Learn more.  

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