It’s flu season.
I’m going to do the whole column on the flu next week, but to set it up, this week we’ll talk about pathogenic (that means “disease causing”) microorganisms a bit and how the human immune system and vaccination works to protect us from them.
First off, it’s important to understand that this world actually belongs to the microbes. We only live here. Microorganisms are defined very simply as living things that are generally too small to see without a microscope. The discipline of Microbiology generally includes bacteria (single-celled organisms like E. coli that live in our guts), viruses (which aren’t actually alive, but play such an important role in biology that they are considered part of the living world), protozoa (complex single-celled organisms that live in water), fungi (like yeasts and molds), algae (photosynthetic organisms that live in the water), helminths (generally parasitic worms, like tapeworm, which are large enough to see but get stuck in microbiology because they are small-ish and can cause some nasty diseases) and a weird group of microbes that usually live in strange places like hot springs and salt mines, called Archea. It’s hard to estimate, because so much of what goes on in the oceans is unknown, but it is estimated that as much as half of all the mass of all living things on Earth is microbes. Only a relatively small percentage of them are potentially pathogenic, but since they are everywhere and there are so many, the opportunities to become infected are many. An interesting fact about “microbes” is that it turns out that the largest living organism on Earth is a fungus (although there is room for argument, with a grove of Aspen trees in the mix. Google Pando). It is a single fungus (its reproductive structures are commonly called the honey mushrooms) that lives in the soil in Oregon that covers about 4 square miles. It is thousands of years old and weighs maybe 35,000 tons.
Almost all of the more serious infectious diseases in humans in the US are caused by either bacteria or viruses. Fungi can cause some serious diseases in people (and some really annoying non-serious ones, like athlete’s foot and ringworm), but they are relatively rare. Parasitic worms and protozoa also cause some very serious diseases worldwide, like malaria and schistosomiasis, but they are fairly uncommon in the US. For the purposes of this discussion on human immunology, we’ll limit our pathogenic microbes to bacteria and viruses.
As I mentioned before, there are probably actually more microbes than human cells in a human. Your average human consists of about 37 trillion human cells and about 40 trillion microbes. The majority of those microbes are harmless and many are even necessary for normal function, like the bacteria that live in our guts. The important thing about all those microbes is that they are harmless where they are normally found, but they can cause disease if they find their way to parts of the body where they aren’t supposed to be. The E. coli in your gut, for instance, is harmless and even beneficial in your gut, but if it finds its way into your reproductive tract or your upper digestive system (as by poor hygiene or by eating contaminated food), it can cause problems.
There are other bacteria that are normally not found in or on people that can cause all sorts of diseases, including some of the worst ones in history, like the Plague. The plague is a disease (actually a few related diseases) caused by bacteria spread by fleas that live on rats. In Europe, beginning in the 1300’s, the Black Death, as it was called, might have killed over half of the entire population, as many as 200 million people and as many as 500 million worldwide. The world population didn’t recover for almost 300 years. It was a major contributing factor to the stagnation of the early Middle Ages. Other dreaded diseases like leprosy and tuberculosis are also bacterial diseases. Many of these devastating plagues have been brought under control by the discovery and use of antibiotics, which are effective against most bacterial diseases. The plague, which used to kill practically everyone who contracted it, is now easily cured by a course of antibiotics.
Source: World Health Organization
Viruses are different. They also cause some horrific diseases, like polio, COVID-19, pandemic influenza, AIDS, measles, mumps, hepatitis, rabies and smallpox, but they don’t respond to antibiotics and tend to be much harder to treat. Smallpox, for instance, used to kill about 20% of all children before they reached five years old. In the twentieth century alone, smallpox killed as many as five hundred million people. Fortunately, since they are hard to cure, we have developed an ounce of prevention for many viral diseases—the vaccine. No one really knows when the idea of vaccination first came up, but it was almost certainly the result of keen observation and experimentation on someone’s part. At some point, someone noticed that people who milked cows didn’t get smallpox as often as other people did, and if they did get it, it wasn’t nearly as severe. Then someone noticed that people who milked a lot of cows often caught a disease called “cowpox”, and it was the people who caught cowpox who avoided the worse of smallpox. I expect somewhere, someone decided to rub themselves with cowpox scabs in an attempt to give themselves cowpox, thereby making themselves less likely to get smallpox. This is probably how vaccination came about. The word “vaccination”, stems from the Latin word “vaca”, which means “cow”. For many years, at least going back to the early 1700’s, people would intentionally infect themselves and their families with the pus from smallpox lesions, in order to, hopefully, give themselves a mild case of the disease, which would make them immune to a worse case. A British doctor by the name of Edward Jenner took up this idea in 1797 and developed the first true vaccine. In the mid-twentieth century, humanity began a great, worldwide program to eradicate smallpox. Vaccines were produced and delivered to every country in the world and teams of people fanned out to all areas to vaccinate everyone they could find. It took many years, but the result was, without a doubt, one of the greatest scientific achievements in all of human history. The last case of smallpox occurred in 1977. We don’t think too much about diseases like smallpox, plague and polio anymore, because they aren’t really part of our lives, but it was not very long ago that that they were just about the most terrifying specters looming over all of humanity. Can you imagine living in a world where, if you had 3 children, it was expected at least one of them would die from an infectious disease before they reached their fifth birthday? Vaccines are truly one of our greatest achievements. Which is why it really frosts my giblets to hear people say things like “vaccines can cause autism” or “I don’t get a flu shot because I did it once and caught the flu from it”. It truly boggles my mind how something as fundamental to human health as vaccination has somehow become a political issue. There’s no end of things people can argue politics about, but vaccination should not be one of them.
First off, that nonsense about vaccines and autism started from a single article published in England which has since been absolutely discredited and retracted. It found its way onto the Internet where a low-level celebrity read it (or someone read it to her). She then went on a talk show spouting nonsense about vaccines causing autism, with the result that a lot of people stopped getting their children vaccinated. The result of that was a resurgence of a lot of diseases causing a lot of kids to get very sick. Let me say this very clearly: there is no link whatsoever between vaccines and autism. Nobody has ever become autistic because of being vaccinated. Ever. If you choose not to vaccinate your children, you are exposing them, and even worse, other children, to the dangers of a host of entirely preventable diseases that can lead to life-long consequences or even death. Vaccines do carry some risk, mostly from allergic reactions, but complications are exceedingly rare, serious complications even rarer still, and compared to the potential consequences of the diseases they prevent, being vaccinated should be a no-brainer.
You also didn’t get the flu from a flu shot. It is impossible to get the flu from a flu shot. The virus used to make the vaccine are inactivated and cannot possibly cause the actual flu. The nasal spray is made from a weakened virus and can, on very rare occasions, cause the flu, but the shot can’t. If you ever got the flu after getting your flu shot, one of two things happened—either you already were infected when you got your shot or you became infected in the week or two after your shot, before the vaccine had a chance to build your immunity. There is a third possibility as to why you got the flu, but it wasn’t caused by the vaccine, either. It was just because the vaccine either didn’t work or didn’t work very well that year. We’ll hit this a little more next time.
The human immune system is a remarkable, remarkable thing. If we could actually see how many potentially pathogenic microorganisms there were out there, we would all probably shut ourselves up in plastic bubbles. Pretty much everything you touch, eat, breathe or drink has microorganisms on it that can potentially make you sick. The vast, vast majority of them will never get the chance to make you sick because your first line of defense—things like your skin, chemicals in your tears, the mucous membranes in your respiratory tract, the acid in your stomach—keeps germs from getting inside where they can get established, multiply and do damage. Of those that make it past those first defenses and actually make it to a place in your body where they can live and cause an active infection, most of them will be eliminated by the second line defenses—things like white blood cells that your body produces to attack anything foreign. If the infection becomes established quickly enough that the nonspecific second line defenses can’t eliminate it, you’ll probably get sick. Even then, though, there is a third line of immune response that is absolutely amazing. It is powerful enough that it can kill off almost anything that has infected you. The only question is whether or not this powerful response can work fast enough to get rid of your disease before the disease kills you. And the even more amazing thing is that, once your immune system gets rid of the infection, that particular type of germ will never be able to make you sick again. You will be immune for the rest of your life (mostly).
So, the obvious question is “Why do I have to worry about getting the flu (or a cold, or strep throat) again if I’ve already had it”? That is a great question, and the answer is that you generally won’t ever get the SAME flu or the SAME cold or the SAME strep throat again. You will get the flu from a slightly different virus. You can get a cold, which is just a very general term for a bunch of symptoms, from a wide variety of viruses. Streptococcus is a large family of bacteria and there are many different strains that can cause infections, and you are only immune to the ones that have made you sick before. Occasionally, however, acquired immunity (the immunity you get from having been infected or vaccinated) can decrease over time and you do become more susceptible to re-infection, either because your immune cells decrease or because the microorganism mutates fairly quickly. That’s why some adults should get booster shots for certain diseases, like tetanus and COVID. We’ll talk more about this and what makes the flu such a big deal next time.