# Vaccines --- **Vaccines** are a way of artificially administering a harmless version of a [[pathogen]] in order for our [[immune system]] to build up it's defense against it—specifically by creating high-affinity [[memory cells]]—before being exposed to it in the real world The general idea of a vaccine is to take the actual pathogen or toxin and render it effectively harmless while still being recognizable enough to our system as to be able to build up a defense against it. There are several different approaches on *how* to achieve this end, depending on various factors such as the type of pathogen, and the technology available. ## Inactivated or Killed Vaccines **Inactivated** or **killed vaccines** render the pathogen harmless by either killing it outright or inactivating them to the point of harmlessness. One way of achieving this is through the use of formeldahide. Although this provides the advantage that there is no way to actually be sick from them, they provide a relatively short-lived protection. As the antigens aren't producing an active infection, there is not enough of a chance to perform [[affinity maturation]] in order to produce high-affinity [[memory cells|memory cells]]. Booster shots contain the same antigen, which allow this step. Some examples of a killed or inactivated vaccine are: the conventional [[influenza|flu]] vaccine (that you get with a shot), and Polio (Salk) vaccine. ## Attenuated Vaccine **Attenuated vaccines** use highly weakened versions of the pathogen so that our bodies can recognize them but they are usually past the point of being actually dangerous. The way that they do this is to just let the culture go and go for a very long time, so that the accumulated mutations render it weak enough to do no real damange. The advantages of using attenuated vaccines are that it can provide a long lasting protection, as the infection stays around long enough for us to be able to make high-affinity memory cells. The disadvantage is that there is the potential for the pathogen to back-mutate back into a form that is dangerous. Some examples of an attenuated vaccine are: measles/mumps/rubella, hepatits A, Polio (Sabin), and the nasal form of the flu vaccine. ## Subunit Vaccine **Subunit vaccines** use just bits and pieces of the vaccine that can be recognized by our bodies as an antigen. The advantages of this type of vaccine are that there is not chance of us getting actually sick. The disadvantage of this type of vaccine is that the protections are short lived and booster shots may be required, as the subunits are not recognized by [[toll-like receptor|toll-like receptors]]. Because of this macrophages, dendritic cells do not recognize them, and thus [[helper T-cells]] do not get activated. Some examples of subunit vaccines are: hepatits B and the meningitis vaccine. ## Toxoid Vaccine **Toxoid vaccines** are used when the agent that actually causes illness is a toxin that a bacteria (or virus?) produces. To make this vaccine we can take the toxin and denature it (usually by heating it up) so that it's shape changes enough that it won't be harmful, but not enough that it isn't recognizable by our system. This is called a "toxoid". The advantage of this type of vaccine is that there is no real way to get sick from it. The disadvantage is that it's protection is short-lived and booster shots may be required. Some examples of toxoid vaccines are: tetanus and diphtheria ## DNA Vaccines **[[DNA]] vaccines** are the newest form of vaccines (that only work on viruses) that trick our cells into making a select few recognizable pieces of a virus. This way, our own cells produces these proteins and it triggers a broad spectrum of immune response. One way to put that DNA into our cells is by using [[plasmid]] DNA into a little lipid molecule. The good target cells for getting these plasmids into are our [[dendritic cells]] (that live just under the skin), as they can load up both their [[MHC molecule|MHC I and II]] molecules with it, which trigger both [[cytotoxic T-cells]]. Another good target for getting the DNA into is the [[muscle tissue]], as muscle cells tend to expel proteins that they make, which puts them into the environment so that [[B-cells]] can come across them. ![[DNA vaccine.png]] The advantages of DNA vaccines is that they are very cheap to mass produce, as once we have the plasmid we want, we can just keep growing colonies of bacteria with them inside it. Another advantage is that it allows us to expose our systems to the antigen in it's natural formation, instead of altering it in some way that makes it harmless. It also has the potential of activating cytotoxic T-cells, helper T-cells, *and* B-cells. The only real disadvantage is that there are none currently approved for use (at least in the US) as of May 2021. ### Moderna/Pfizer/J&J [[COVID-19]] Vaccine These vaccines pack the RNA (or DNA in J&J's case) into a [[lipids]] molceule, which can enter our cells via [[animal virus|membrane fusion]]. It does need to be kept very cold, as RNA is very unstable on it's own, especially when it is single stranded. The extra [[hydroxyl]] on the RNA is also very reactive and likes to cling to anything it can. The reason why Moderna and Pfizer need two doses is that it just gives an extra boost—it's basically the same shot twice. J&J only needs one shot, but it's a bit less effective probably due to it needing to use an adenovirus to help it. ## Conjugate Vaccines **Conjugate vaccines** are used for bacteria who have [[capsule|capsules]], because these capsules are made of carbohydrates, which are generally [[B-cells#T-Dependent Antigen|T-independent antigens]]. Because these don't produce [[memory cells]], that's not exactly ideal for a vacicne. The reason capsules can't flag down [[helper T-cells|helper T-cells]] is that carbohydrates cannot be loaded onto [[MHC molecule]] molecules. But if we attach a protein to the [[B-cells#T-Dependent Antigen|T-independent antigens]], then when that antigen is taken in, it *can* load up the protein portion, and get that [[helper T-cells]] activity. ## Vaccines for Pregnant People Whether or not a vaccine is safe for pregnant people depends on the type of vaccine it is. It is not recommended that [[pregnancy|pregnant]] people get live vaccines, as there is a risk of vertical transmission to the baby. Attenuated vaccines are okay, and the CDC recommends TDAP and flu shots for every pregnancy, but MMR should be given before or after the pregnancy. ___