Vaccines, Transplants, and Donation
Before you ever get truly sick, you can "train" your defenses so they already know what to do the day the real agent arrives. That is exactly what a vaccine does. And when someone's defenses fail, or an organ stops working, the solidarity of other people, by donating blood or organs, can save their life.
What a vaccine is and how it works
When a baby goes to the health center, they get a shot even though they are healthy, and thanks to that they are protected for years against serious infections. How can a harmless substance train our body to fight a danger that doesn't exist yet?
The process, step by step: the vaccine provides antigens, the lymphocytes recognize them and make antibodies, and some remain as memory lymphocytes. If the real agent arrives later, the response is fast and strong, and the person doesn't get sick or gets only mildly sick.
Types of vaccines and their limits
Not all vaccines contain the same thing. Some contain the whole virus attenuated (alive, but so weakened that it doesn't cause the disease in a healthy person). Others carry the inactivated (dead) agent or just a fragment, such as a protein from its surface. A fragment is enough: the lymphocytes learn to recognize that protein, and the real virus carries that same protein, so it will be identified and neutralized.
Vaccines with an attenuated agent have one limitation. In an immunocompromised person (with very low defenses), the weakened agent could multiply and cause disease. Fragment vaccines don't have that risk because they don't contain a whole agent capable of reproducing.
Why some protections weaken
Immune memory doesn't last the same length of time for every agent. With some vaccines, such as tetanus, the amount of antibodies and memory cells drops over the years. That is why booster doses are given to "revive" the memory. Others produce very long-lasting memory with few doses. Vaccines are also evaluated by their benefit and risk: serious adverse effects are extremely rare, and the disease they prevent is usually much more dangerous.
Explain what a vaccine is, what it contains, and how it prepares the body to defend itself against a disease without suffering from it.
Explain what a vaccine is, what it contains, and how it prepares the body to defend itself against a disease without suffering from it.
The tetanus vaccine requires booster doses every few years, whereas others provide lifelong protection with few doses. Explain, based on how immunological memory works,…
The tetanus vaccine requires booster doses every few years, whereas others provide lifelong protection with few doses. Explain, based on how immunological memory works, why some protection weakens over time.
A research team develops two experimental vaccines against a new respiratory virus: vaccine A uses the whole attenuated virus, while vaccine B introduces only fragments…
A research team develops two experimental vaccines against a new respiratory virus: vaccine A uses the whole attenuated virus, while vaccine B introduces only fragments of the external protein that the virus uses to attach to human cells (surface antigen).
- a) Justify why the body of a person who receives vaccine B will be able to neutralise the real virus if they come into contact with it later on, even though the vaccine only contained a fragment.
- b) During trials, it is observed that in immunocompromised patients, vaccine A can cause mild symptoms of the disease, while vaccine B is completely harmless but requires a booster dose. With this data, justify which of the two vaccines you would recommend administering as a priority in a hospital to elderly people or those with weakened immune systems.
The vaccination schedule and herd immunity
For example, in childhood and adolescence, vaccines such as BCG (tuberculosis), hepatitis B, the MMR (measles, mumps, and rubella), and the human papillomavirus (HPV) vaccine are given. Some are given at specific ages because the immune system responds better at certain times, or because they need several doses or boosters.
Risks, benefits, and limits
Social and economic benefits: fewer sick people, fewer deaths, fewer hospitalizations, fewer days missed from school or work, and less spending on treatments. Risks: almost always mild discomfort (pain, fever); serious reactions are very rare. Limits: no vaccine protects 100%, some need boosters, and viruses can change, so science updates them.
State what a vaccination schedule is, why there are vaccines administered at specific ages, and name two vaccines included in Mexico's childhood and adolescent…
State what a vaccination schedule is, why there are vaccines administered at specific ages, and name two vaccines included in Mexico's childhood and adolescent vaccination schedule.
The two diagrams represent the same outbreak in two populations with different vaccination coverage (green: vaccinated people; gray: unvaccinated people; red: infected…
The two diagrams represent the same outbreak in two populations with different vaccination coverage (green: vaccinated people; gray: unvaccinated people; red: infected people; the orange crosses in diagram A indicate blocked transmissions). Explain why in diagram A the infection does not advance whereas in B it spreads in a chain reaction, what this "herd immunity" consists of, and what risk is posed by a decrease in vaccination coverage.
Blood donation
In an emergency surgery, several liters of blood are needed to save a life, but this tissue cannot be manufactured in a laboratory. Where does the hospitals' blood come from, and why isn't it enough to collect it only when a catastrophe happens?
Basic requirements: being an adult, being healthy, having a minimum weight (around 50 kg), not having recently had certain infections, and passing a medical checkup and a blood test. Donations are made at blood banks and hospitals.
Explain what it means to be a blood donor, what basic requirements are asked of donors, and why regular donation is necessary even when there are no emergencies.
Explain what it means to be a blood donor, what basic requirements are asked of donors, and why regular donation is necessary even when there are no emergencies.
In Mexico, a person can donate blood from the age of 18 if they meet the requirements. Each donation (about $450\ \text{mL}$) is separated into three components (red…
In Mexico, a person can donate blood from the age of 18 if they meet the requirements. Each donation (about $450\ \text{mL}$) is separated into three components (red blood cells, plasma, and platelets) and can help up to three patients, but these components expire: platelets last only about $5$ days and red blood cells about six weeks. If a hospital needs $25$ units of blood components per day, calculate how many donations are needed as a minimum each week and reason, based on the expiration of the components, why donating only after major disasters is not enough.
Transplants and organ donation
Blood groups and compatibility
Red blood cells carry markers (antigens) on their surface that define the blood group: A, B, AB, or O (plus the Rh factor, positive or negative). If blood from an incompatible group is transfused, the recipient's antibodies attack the donated red blood cells. That is why compatibility is checked before a transfusion or a transplant. For organs, besides the blood, other matches between donor and recipient are looked for.
Rejection
Rejection can occur in an organ transplant. Explain why the recipient's immune system attacks the transplanted organ, what blood groups and compatibility are, and what…
Rejection can occur in an organ transplant. Explain why the recipient's immune system attacks the transplanted organ, what blood groups and compatibility are, and what medications are used to prevent rejection.
Health within the ecosystem
Viruses, bacteria, and people do not live in isolation: they are part of an environment with other living things. To understand why a disease spreads, or why vaccinating a community protects everyone, it helps to look at that whole picture.
An infectious disease is a relationship within the ecosystem: the microbe (agent) lives at the expense of a host. When most of the population is vaccinated, that relationship is cut and the balance changes: the agent hardly finds any hosts and stops circulating. In addition, many diseases pass from animals to people, which is why the health of people, animals, and the environment are connected.
On an internet forum you read this statement: "We shouldn't get the new vaccine against pathogen X. In its clinical trial with 10,000 volunteers, 0.3 % developed fever…
On an internet forum you read this statement: "We shouldn't get the new vaccine against pathogen X. In its clinical trial with 10,000 volunteers, 0.3 % developed fever and muscle pain. A safe vaccine should have zero risk before being authorised."
- a) Knowing that natural infection by pathogen X causes severe complications in 8 out of every 100 infected people (8 %), compare both figures and explain what the benefit-risk balance means in the authorisation of medicines.
- b) Refute the statement by arguing biologically why it is impossible to guarantee "zero risk" in any medical treatment and what guarantees the phases of clinical trials provide before a vaccine reaches the general population.
Summary
Back to the beginning: training your defenses with a vaccine keeps you from getting sick, and donating blood or organs can save lives.