Why get Vaccinated and How do Vaccines Work?

Other than sanitation (especially clean water, proper food handling, and reducing human exposure to rodents), I cannot think of anything that has done more to reduce childhood mortality, relieve human suffering and extend human life expectancy than vaccines.

What is a vaccine? In general, a vaccine is something given by mouth (e.g., polio vaccine), intranasally (e.g., one version of the flu vaccine), or by injection (the majority of vaccines) that exposes the body to a part (e.g., a protein) or the whole (but an inactivated or weakened form) of the organism that causes the disease that the vaccine is intended for such that the body will then mount an immune response (primarily antibodies, but it can be much more than that) that will be protective to some degree when the vaccinated person is later exposed to that infectious threat.

Why do vaccines make such a difference to our public health?

Let me start with a disclaimer. This particular blog post is intended for readers who don’t understand anything about vaccines, immunology or infectious diseases. Therefore, I will necessarily have to oversimplify my explanation. There are many nuances to all of these subjects, and I am not going to explore these. In fact, I am going to try to avoid as much medical jargon and as many technical terms and concepts as possible. To do so, I am going to largely use analogies. Like all analogies, they can help people understand general concepts, but they inevitably have their limits in that when carried too far, the analogy always begins to fall apart.

So, here we go. Imagine that you are the head of Homeland Security for the U.S. You are informed that our intelligence agencies have identified a threat of attack on our homeland within the next six months with a moderate degree of confidence. The problem is, the agencies are not yet certain of the type of attack, the number of people involved in the planned attack, the identities of any of the potential attackers, or how they plan to enter the country.

This head of Homeland Security is going to be our analogy for you back in 2021 as we were in a pandemic and you knew that there was this invisible virus out there awaiting to attack and invade the bodies of those who were susceptible to infection (which was almost everyone).

Of course, one approach that the head of Homeland Security could take is to realize that we already have many systems in place to thwart entry into the U.S. by potential terrorists and to prevent potential attacks, such as our passport system, our no-fly lists, TSA and their security measures, the Coast Guard, the Border Patrol, various security check-points, the U.S. Postal Service and a host of other security measures, and to feel confident that chances are, the potential terrorists could not evade all of these measures. And, the director might assume that even if one or more of the terrorists did get through, the likelihood is that any attack would be relatively minor and local in nature. Similarly, this is the decision that many during the pandemic made in declining the vaccines, realizing that even though we had no idea as to who might be carrying the virus and end up infecting us, that we have many systems in place to protect us from attacks by viruses, and that even if the virus was successful in infecting us, the chances were that the illness would be mild and limited.

Many of us might not have the same degree of confidence as that director of Homeland Security given that sophisticated terrorist networks evolve. They learn from past mistakes and they learn where the obstacles in our system of barriers and protections are and how to potentially get around them. So too, viruses evolve. Certain types of viruses (RNA viruses – a group that includes the influenza virus and SARS-CoV-2) evolve faster, and the larger the number of humans they infect and the larger the number of species of animals that they infect, the faster and more dramatically they evolve. Just as terrorists learn how previous attacks were stopped, viruses “learn” how our immune systems are blocking them, and they may develop ways to get around those immune defenses. It is unlikely that viruses will acquire the ability to defeat every one of our defenses, but just as for terrorists, they don’t have to in order to inflict a great deal of harm. Even with our most horrific domestic terrorist attack on 9/11, the terrorists didn’t evade every line of our defenses – one of the attacks was thwarted by our last line of defense: regular Americans who were passengers on the plane and who bravely overtook the terrorists at the cost of their own lives. Similarly, when we are exposed to a virus, it is not a single virion, but generally hundreds, thousands or tens of thousands. Many of those virus particles will be stopped in their tracks before infecting us, but it only takes a small number of successful virus particles getting through these defenses and infecting cells to cause potentially serious harm.

Although I have no law enforcement or national security experience or expertise, I would imagine that most directors of Homeland Security would not want to take the chance that our current routine barriers to entry and processes would catch all of the potential terrorists before they could enter the U.S. (In the analogy, the terrorists are the SARS-CoV-2 virus and the U.S. is our body consisting of cells which the virus can infect if it gains entry.) I imagine that one piece of information that would be critically important to the director in an effort to thwart this planned attack would be to know by what route the terrorists plan to enter the U.S. – land, sea, air – so that barriers to entry could be enhanced. Using our analogy, though we didn’t know who was carrying the virus and would be a threat to us (because at that time our testing was inadequate and because we knew that a substantial number of people that were infected and contagious were asymptomatic and didn’t realize that they might be contagious), we did know how the virus planned to enter our bodies – through aerosols that we breathe in through our nose and mouth. Thus, for those who wanted to enhance their defenses against virus particles trying to invade by this respiratory route, there were a number of interventions that could be used – e.g., increasing ventilation indoors; utilizing air purifiers and air filters; avoiding large numbers of people in poorly ventilated spaces; physical distancing; and utilizing well-fitting, high-quality masks.

I would suspect that another critical piece of information for the director besides the route by which the terrorists plan to enter the country would be to have the identification of the terrorists and a description of each. That would allow our surveillance and security checks to be far more focused and decrease the potential for a terrorist to slip by undetected. Having their descriptions would be great; images would be better; and having their finger prints and DNA would give us positive identification, especially in the case that we were able to make a preemptive attack on the terrorists before they could attempt their attack on us.

So, too, if our bodies have a description of key distinguishing and identifying features of the virus that threatens us, our immune systems can be better prepared, can respond much more quickly and precisely, and we can have a better chance of stopping more of these potential invaders at our border before they can infect our cells. That is what vaccines do. They give us a relatively harmless piece of the virus (e.g., the spike protein in the case of the COVID-19 vaccines) or a “killed” or inactivated entire virus that allows our immune systems to learn to recognize this potential invader much like having the virus’ image and fingerprints, and enable the immune system to respond much faster the next time the body is exposed to that invader.

That faster response helps prevent serious illness in a number of ways. One way is that when antibodies are already preformed against the invading virus, the antibodies have the potential to “neutralize” the invading virus – i.e., prevent the virus from ever invading a cell and causing infection. Once virus enters a cell, the antibodies no longer have a way to get to the virus until the virus has replicated many times over and leave that cell to invade other cells. Just like an invading army, it is much easier to stop a team than a squad of soldiers, and much easier to stop a squad than a platoon, and so on, and much easier to defeat the invaders before reinforcements arrive. Thus, when antibodies are at the ready, fewer invading virus particles will get through and invade cells. Once in cells, the invading virus particles get thousands or hundreds of thousands of new virus recruits that are made in the cell and released to infect other cells. Thus, the more virus particles that are stopped before they are able to infect and reproduce inside cells, the lower the total number of infecting virus particles (we refer to this as viral load), and for many infections, viral load has some correlation to severity of illness. So, while many people might be able to rely on the normal defenses that are already in place and might have only a mild illness as the result of an infection, vaccines greatly increase and enhance the defenses and increase the odds that the illness will not be severe. We saw this over and over again in hospitalized patients with COVID-19 – those requiring hospitalization, those requiring critical care, and those dying from COVID-19 were many times more likely to not have received the vaccine.

To return to our analogy, let’s say that the director now becomes aware of intelligence identifying the location of the terrorists who are planning the attack on the U.S. They are meeting in a building in an urban center of another country. Unfortunately, it is still not known precisely who the terrorists are or how many there are. Bombing the building would be sure to take the terrorists out and prevent the attack on U.S. soil, but would also be sure to cause much collateral damage in terms of economic damage, injuries and loss of innocent lives, not to mention political fall-out. A more targeted approach – a raid of the building, a room-to-room search, and detaining of individuals until it could be determined whether they are one of the terrorists would be highly risky and difficult since the identities of the terrorists are unknown.

In the case of SARS-CoV-2 infections, a similar dichotomy exists once a would-be virus invader has been sensed. The part of our immune system that is on guard for invaders before antibodies are developed can only detect that the invader is different from things that are normally part of our body, and instead of the precision-targeting of the invader like a sniper would perform, it must resort to releasing all kinds of chemicals (chemokines, cytokines among them) and responses that are analogous to firing a tank, dropping a large tonnage bomb, or throwing a grenade at the invaders. Like the option of the director in recommending to the President that the building housing the terrorists be bombed, this non-specific response will often at least slow down the virus invaders, but also cause collateral damage – e.g., injuring nearby cells and tissues and causing uncomfortable symptoms.

The extent of this exaggerated, non-targeted response is also often related to how similar the invading virus is to prior viruses that the person has been exposed to. For example, the SARS-CoV-2 virus was what we called a “novel” virus, meaning that as far as our immune systems were concerned, the vast majority, if not all, people were unlikely to have any preexisting immunity to this virus. The same thing happened in 1918 with the pandemic Spanish flu [A(H1N1)] virus. In both cases, the viruses were novel and in many, especially children in the case of SARS-CoV-2 and young adults in the case of the Spanish flu, the body responded to the infection with what is called “cytokine storm,” an exaggerated release of chemicals disproportionate to the direct threat of the virus that itself did more damage than the virus and caused organ damage to the patient, sometimes resulting in death. Vaccines do not only improve the immune response by having antibodies at the ready for a much faster response and potentially diminishing the viral load resulting from infection; in some cases, and this appears to be the case for COVID-19, they moderate the immune response significantly decreasing the chances that someone will develop cytokine storm.