As a medical virologist for over 30 years, I and many of my colleagues have been amazed what we have heard about the COVID-19 vaccine and natural immunity after infection by the virus that causes COVID-19, called SARS-CoV2. So much clear-cut information is known about this disease process, yet policies are being made that ignore this information. So, let’s discuss these facts in simple terms. Here are the six basic facts of viral immunity, regardless of the virus:

1. Virus infections induce life-long immunity. This includes most of the viruses we are familiar with, such as measles, polio, human papillomavirus, mumps, and rubella. The reason is simple: the immune response completely destroys the virus. There are a few exceptions where the virus is kept at bay but persists (such as chickenpox) but overall when someone fight offs a virus, they are immune for life. Let’s discuss why this is true.
2. The immune response that kills the virus includes multiple key parts. Here we need to get a bit more technical. We have all heard about the antibodies that our immune system uses to attack a virus. But this is a small part of the way our immune system attacks a virus. The more important part is the white blood cells (called T lymphocytes) and the memory lymphocytes. Think of the antibodies as like handguns and the T lymphocytes like cannons. And, using this analogy, think of the memory lymphocytes as battleships.
3. The T and memory lymphocytes are the key to life-long immunity. There are genetic diseases where people can’t make antibodies and these people can live into their 40s. Yet people who lose their T lymphocytes (as with AIDS) die of infection within 1 year or so. So why do we only hear about antibodies and not T lymphocytes when it comes to COVID-19?? The answer is simple: the antibodies are easy to measure whereas the T lymphocytes immune response to the virus require more complicated measurements.
4. The memory lymphocytes live for our entire life, and activate years/decade after we recover from a specific viral infection to stop the virus from infecting us again. Indeed, this is the basis of life-long immunity. These cells are called memory lymphocytes because they remember the specific proteins unique to the virus, and then re-activate both our antibodies and T lymphocytes to kill the virus.
5. There is a poor correlation between the antibody levels and the T lymphocyte/memory cell levels. The antibodies levels can be low, even nondetectable yet the T lymphocytes and memory lymphocytes can still be robust. Indeed, that is the whole point of the memory cells. They respond immediately when the virus re-enters the body and they kill it. It will take a few days for the memory lymphocytes to reactivate, but they do this with gusto. This leads us to the last point.
6. An immune person (vaccine or natural immunity) can still get infected BUT will invariably destroy the virus and get only a mild illness. We call this sub-clinical infection. It is simply not possible to recover from a viral infection, and then die years later of that same virus unless the person has become immunocompromised, and even in those cases it is unusual.

Okay, that is it for the basics of virology. Now let’s apply this information to real-life infections. But before we get to COVID-19, let’s use some other viruses and their vaccines that we know a great deal about as examples: measles and hepatitis B.

Measles is actually the best example to study. It is transmitted the same way COVID-19 is, but is even more infectious (some medical books list measles as the most infectious of all viruses). This means that if you are in a room with a person who has measles (or even if he left the room a few hours earlier!) and you are not immunized, you will become infected, no ifs, ands or buts. Excellent vaccines against measles started in 1963 and either 1 or 2 doses at age 1 and age 5 provides life-long immunity to the vast majority of people. This is easy to prove. Before the vaccine, 3 to 4 million people each year in the USA got measles. Since the vaccine, the number of cases per year in the USA ranged from 37 to 1,282. And, when measles cases do occur, 90-100% of the infected are unvaccinated/have no proof of vaccination. Remember, unless you are immune to measles you will get the infection, and many people got the vaccine 30-50 years ago! Some of these outbreaks occurred in NYC where many of tens of thousands of people were exposed, but did not get sick. This is such a simple yet solid proof of life-long immunity!

Another important point about measles vaccinations is that is has been documented that the antibody response and T lymphocyte/memory cell responses are independent of each other. This also was shown with another virus where a good vaccine has been available for decades, hepatitis B. To quote the authors: “These data suggests that hepatitis B vaccination can confer long-term immunity and that immunological memory can outlast the loss of antibody”. When you think about it, this makes perfect sense. The cells that makes the antibodies eventually die if they are not exposed to the virus. But the memory lymphocytes stay with us our entire lives and if the virus returns, they quickly signal the body to make more antibody and T lymphocytes to kill the virus. Re-infection is simply Mother Nature’s booster.

This now brings us to COVID-19. So much is known about the disease. The disease is rarely serious in children, unless they are obese or have some serious pre-existing health problem. The disease in adults is most severe in those who are obese and have serious pre-existing health problems, like diabetes, heart failure, or kidney failure. It is well documented that the two dose Pfizer/Moderna or one dose J&J vaccine offer nearly 100% protection against serious disease.

So, what is known about re-infection by the COVID-19 virus after immunizations? A lot. Here is what the CDC says: “Even when fully vaccinated people develop symptoms, they tend to be less severe symptoms than in unvaccinated people. This means they are much less likely to be hospitalized or die than people who are not vaccinated”. This is what we would predict from point 6 above. The medical literature is much more definitive. As one example, recently published in The Lancet (a major medical journal, some say THE major medical journal) looked at people who recently were hospitalized with severe COVID-19 and their vaccination status. Of the 969 people who were admitted to the hospital with severe COVID, 82% were unvaccinated. Most of the vaccinated patients (partial or complete vaccination) had subclinical or mild disease, just as we would predict from point 6, and were hospitalized for non-COVID reasons. Only 1.4% of fully vaccinated people had severe COVID-19, but these people were all older than 80 years of age and had serious other medical problems to begin with, where even moderate COVID-19 could push them to be seriously ill.

This leads us to the last point. We hear a great deal about declining antibody levels to COVID-19 as being the basis to require a booster. You can answer this: does this make medical sense? The answer is no and is seen clearly in the points above. So why is it being done? The answer is that the companies that make the vaccine will profit greatly by requiring all to get boosters and they have the ability to relentlessly push their message to the public. But, clearly, the best public health option is to give even one dose (which in itself offers excellent protection against COVID-19) to those in the USA and around the world who still haven’t got the vaccine. This will greatly help curb the pandemic, as would allowing other companies to make the approved vaccine by waiving the patent rights; the technology for making these vaccines is well established. Giving boosters to people who are at low risk of severe disease such as the fully vaccinated instead of the unvaccinated is going against public health. It really is as simple as that.

As a physician who specializes in viral infections, I have tried to show you the simple basic facts known about viral infections and vaccines. But allow me to end with a strong plea, which echoes the position of the WHO. Let’s do all we can to insist that the vaccines go to those who are now completely unprotected against this virus. This is a safe and effective vaccine and unless a person is 100% certain they had the disease and recovered; I would strongly urge they (like I did) get vaccinated. And, most importantly, if you have recovered from the infection or been fully vaccinated against COVID-19, rest assured that you are well protected against re-infection; indeed if you get exposed again to the virus, it will boost your immunity.