Understanding how vaccines work in large populations requires some depth in understanding of vaccine development, clinical trials, medicine, immunology, virology , epidemiology, population dynamics and human behavior. Most Americans lack a basic understanding of these subjects. It is not because Americans are “stupid,” it is because most of us did not pursue a career in medicine or science. Unfortunately average citizens with a lack of general scientific knowledge in biology and medicine and very vulnerable to misunderstanding, oversimplification faulty conclusions about viruses and vaccines. The problem is compounded by huge amounts of disinformation, which is readily spread via social media such as Facebook and Twitter. Vaccines and COVID have also been politicized- often by politicians or right wing media who also lack scientific understanding.

To begin with, the notion that a human can just get an injection of a vaccine, for example the polio vaccine, and then be forever immune and protected from a challenge or exposure to poliovirus is a fallacy. Dr. Fauci said right from the start that in order to achieve “herd immunity” a certain percent of Americans would need to be fully (meaning one initial vaccine plus booster) vaccinated. He also added that we did not know what that percentage was… it might be 50%, it could be as high as 80%. Why though?

First, in each individual vaccines are not 100% effective. In fact the criteria for efficacy of COVID vaccines- which were developed rapidly and under emergency conditions- was >50% efficacy. This implies that of 100 patients tested, only 50 would develop a measurable immune response sufficient enough to neutralize the virus. Vaccines do not need to be 100% effective (I.e. 100 of 100 people immunized develop neutralizing antibodies) to work. For every 100 people immunized there is going to be a spectrum of subjects that produce a robust immune response vs. others who produce a weak immune response. This stratification can be overcome however, by the use of boosters. This is because of how your immune system works. At first challenge with the virus (or antigen) it can take several days for the B-cells (which produce neutralizing antibodies) to multiply enough to mount a robust immune response. In addition your body has both a humoral and cellular immune response, so T-cells will eliminate infected cells and tissues. Because of the presence of memory cells, when a patient is boosted (second challenge) the immune response is much more rapid and robust, wiping out the challenge virus quickly. This is why children tend to get a ton of cold viruses, but adults don’t.

If you could, on a single day, immunize 330 million Americans with the COVID vaccine (100% immunization) followed by a booster, it is very likely that the virus could be, at least temporarily, eradicated. However a mass vaccination like this is not possible due to logistical issues. Due to the rate of vaccine manufacturing, distribution and administration it took months to reach the point where we even had 50% of adults vaccinated. Children could not immediately be vaccinated, due to the lagging data on the pediatric clinical trials and safety concerns.

In essence we ended up with a partially vaccinated population, where not all Americans were vaccinated and even fewer were fully vaccinated (meaning a booster). There was also a certain percent of the population that just refused the vaccine. While the mass vaccination did reduce the spread of COVID, new cases and deaths, the virus was never eliminated and continued to propagate in unvaccinated individuals. COVID was also still propagating outside the United States, therefore our population both vaccinated and unvaccinated was still susceptible to new strains of COVID arising either domestically or abroad.

The other misconception about the COVID vaccine, was that people (wrongly) think that if you’re vaccinated that implies you cannot be infected, nor can you transmit the virus to others. That might true for other vaccines such as smallpox or polio, but as already mentioned vaccines are rarely 100% effective. Being vaccinated against polio does not guarantee you cannot be infected. If properly vaccinated and boosted it guarantees that if you’re exposed to polio that you won’t get sick or will only get minor symptoms. In reality the COVID vaccine works more like the flu vaccine, in that the vaccine is based on a certain prevalent strain of virus and may or may not fully protect you. In fact the medical evidence showed that fully vaccinated individuals- while they could be infected with COVID- did not develop serious or life threatening symptoms. These vaccinated individuals therefore might only have minor cold virus symptoms and could spread the COVID virus to others. The unvaccinated population then is more susceptible since they are basically unprotected.

The other factor in COVID is the mutation rate. Coronaviruses (and RNA virus in general) can mutate rapidly, and subsequently evade the immune system. The virus mutates much faster than humans can design new vaccines to protect against each new strain. Scientists have tried to stay ahead of the viruses by making predictions about which variant will arise next, or by making cocktail vaccines that protect against multiple variants (such as the bivalent vaccine).

Human perception and behavior also affect vaccine uptake. Because of the huge amount of disinformation and the existence of anti-vax pseudoscience and conspiracy theories, many Americans just avoided the COVID vaccines. Several of the prominent anti-vaxxers have died from COVID. Some American’s perceptions about COVID such as “I won’t get sick” or “it’s just like a head cold or the flu” or it’s not dangerous unless I have other medical conditions, or it only kills old people have also inhibited vaccine uptake. Aside from having to go and get vaccinated and boosted, the day after your vaccination you may feel rotten or miss work or school, a side effect that wasn’t common with other vaccines. If you’ve ever had the shingles vaccine plus booster you may know what I mean.

The end result of all this is that vaccine effectiveness and viral transmission depends on a whole bunch of factors and variables that aren’t easily modeled or predicted. When the pandemic began, most scientists agreed that the only way out of the pandemic was herd immunity achieved by mass vaccination, and that could take two years. They were largely correct, despite the oversimplified, scientifically flawed counter arguments that politicians and non-scientists have made.

Misinformation and flawed concepts are propagated by laymen because they are easily reduced to simple sentences and easily spread. Therefore you hear “the COVID vaccine doesn’t work, because my uncle got vaccinated and he still got COVID.” Or “masks do nothing.” These type of statements are oversimplifications, the first one drawing a conclusion on the vaccine from one person rather than large populations, the second one making a blanket statement that isn’t supported by data.

The vaccines did work, they just didn’t work in the way most people thought they would work. But that is because most people’s concepts of how typical vaccines work did not apply to COVID. The reality of polio and smallpox is that those viruses did not immediately disappear, it also took time for mass vaccination to eliminate the viruses in the population.