Part I: How Do Vaccines Work?
I’m a bit excited to talk about this one because this is one of my fields of study. Because there is lots of good information about vaccines, I decided to create two posts. This first one is about the immune system and how vaccines work with it.
Innate versus Acquired Immune System
In order to understand how vaccination works, we must first go over the basics of the immune system.. This video goes into detail about some of the specifics, but for brevity's sake, there are two parts to the immune system to know: the innate and the acquired. The innate immune system acts as your body’s guards and foot soldiers, each of its many cell types acting as a first line of defense against bacteria and viruses. These cells smell out intruders, consume bacteria, destroy virus-infected cells, and tell other cells how to respond to the infection. But because this first line of defense is uniform between all people, it is easier for pathogens to adapt to it. Some bacteria are able to hide from immune cells and some viruses can keep their infected cell just healthy enough to avoid detection. This is where the acquired immune system comes in.
Certain innate immune cells will attach torn-off chunks of bacteria and viruses to their surfaces and transport these chunks to the lymph nodes, where the acquired immune system cells live. Acquired immune cells have proteins on their surface that are extremely good at recognizing and binding to one very specific protein or molecule, like a puzzle piece. Each of these acquired immune cell puzzle pieces are unique. The innate immune cell fits the germ chunks into every acquired cell puzzle piece until it finds a match. The matching acquired immune cell replicates, and its progeny spread out into the bloodstream. There are several cell types within the acquired immune system; some will seek out and destroy cells infected with their specific virus, call other immune cells to the site of infection where they detect their specific pathogen, or produce antibodies, small proteins which bind to their specific pathogen in order to disable it or make it easier to track and catch. Once an infection is killed off, these mature acquired immune cells will live in the lymph nodes for the rest of your life and will continually produce antibodies to quickly kill off the invaders if they ever come again, making you effectively immune to that specific disease.*
The Role Of A Vaccine
The goal of vaccination is to create this acquired immune response in a person without them having to catch the disease. This is a careful balancing act; one has to cause an infection that is strong enough for the immune system to see the pathogen as a threat but is also weak enough to not cause any major symptoms. The easiest type of vaccine to produce is an inactivated vaccine, where one kills the virus you want to immunize someone to and injects its remains into the patient. The dead virus can’t harm the patient and the immune system will still respond to it, but this virus won’t be seen as a major threat. The immune system calibrates its response based on how much of a threat the pathogen poses, so the weak response to a dead virus might not be enough to defend against the living disease should the patient ever catch it. This is where booster vaccines come in; if a patient is given many doses of a dead virus over several months, the quantity can convince the immune system that this virus is a legitimate threat.
The other classical type of vaccine is the live attenuated vaccine, made by taking the virus and altering it to make it less deadly. This is usually done by breeding a strain of the virus in another medium, such as cell cultures, eggs, or live animals, until it’s so good at infecting that species that it partially ‘forgets’ how to infect humans. In a healthy person, this altered virus hits this balancing act well; it will cause a small infection that will trigger a strong, lasting antibody response but won’t be able to spread fast enough to cause any noticeable symptoms. The problem with this type of vaccine is that it can’t be given to immunocompromised patients or anyone with a weaker immune system, such as newborns and the elderly. If a patient’s immune system can’t easily kill off this attenuated virus, then it’s no different than just infecting them with the disease.
Popular Question
Now, I’d be remiss if I didn’t take this opportunity to talk a bit about the myths surrounding vaccines. In fairness, fears about vaccines are as old as inoculation itself, as injecting stuff into someone’s blood is an inherently scary concept. When Edward Jenner developed the first modern vaccine, using cowpox as a kind of naturally occurring attenuated vaccine for smallpox, mass fear spread at the idea of polluting the blood with animal matter. Variolation, a predecessor to modern vaccination, was also opposed when it was introduced to Europe, in part due to racism toward the practice because it was first introduced by slaves from West Africa. The modern anti-vaxxer movement started with a single paper published in 1998 by Andrew Wakefield, claiming to have found a link between the MMR vaccine and autism. The study in question only had twelve subjects; autistic children who’d received the MMR vaccine around the same time they were diagnosed with autism. Starting before these results were even published, Wakefield held press conferences demanding the discontinuation of MMR, even though his study hadn’t yet been peer reviewed. It would later be discovered that he’d secretly received £55,000 from a legal group seeking evidence to use against vaccine manufacturers. Wakefield has since lost his medical license and was investigated for fraud. It’s important to remember that one scientist saying something doesn’t make it true, it’s only when the majority of scientists in the relevant field of study all say the same thing that we can begin to believe a theory is accurate.
Other vaccine myths are:
Vaccines contain unsafe toxins, such as formaldehyde, aluminum, and mercury: vaccines contain non-toxic amounts of these substances to act as preservatives and sterilizers. The body naturally contains trace amounts of aluminum and the metabolism produces trace amounts of formaldehyde, more than the body would receive from a vaccine. The mercury in some vaccines is thiomersal, an organic compound which prevents the growth of bacteria and fungi in the vaccine which could harm the patient. Thiomersal is a compound that contains an atom of mercury in each molecule but this doesn’t make it significantly toxic, just like how salt contains chlorine but isn’t toxic and water contains hydrogen but isn’t flammable. Also, thiomersal hasn’t been used in vaccines since 1999 due to public fear.
Vaccines should be more spaced out, babies shouldn’t be receiving so many so young: children are at their most vulnerable to disease when they’re newborns. Receiving these vaccines so young is meant to prevent these diseases when children are at their most vulnerable. The vaccination schedule that doctors recommend is based on decades of research on when is the best time to receive these vaccinations.
Next up, I’ll talk about the vaccine development process, updates on a Covid-19 vaccine and how we insure vaccine safety.
*Technically, having an antibody response makes you resistant to the disease, not completely immune. There are a few diseases that are able to weather an antibody response and make you somewhat sick or allow you to spread the virus even if you have already had the disease. This is why health organizations are saying you should continue wearing a mask and practicing social distancing even if you’ve had COVID-19; we don’t yet know how resistant having coronavirus makes you to reinfection.
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Image credit: Creator: MarianVejcik | Credit: Getty Images/iStockphoto
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