Vaccines, transplants and donation

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 the difference between preventing a disease and curing it, using a vaccine and a medicine as examples.

Explain what mild side effects can appear in the days after a vaccine and why they are usually a sign that the immune system is responding.

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).

1. 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.
2. 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.

State what a vaccination schedule is, why there are vaccines administered at specific ages, and name two vaccines included in Spain's childhood and adolescent vaccination schedule.

The two diagrams represent the same outbreak in two populations with different vaccination coverage (green: vaccinated people; grey: 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.

A person claims: "I don't get vaccinated because I never get ill". Analyse this argument taking herd immunity into account, and reason what would happen if many people thought the same way.

Measles is one of the most contagious viruses in existence: to maintain community or herd immunity and halt its transmission, at least 95 % of the population needs to be vaccinated. In a town of 20.000 inhabitants, vaccination coverage has dropped to 86 % over the last two years. Living in this town are Clara, a 4-month-old baby who is not yet old enough to be vaccinated, and Sergio, a boy undergoing cancer treatment who cannot receive the vaccine because of a weakened immune system.

1. a) Predict what will happen in that town if a person infected with measles attends a crowded party, comparing the current scenario (86 %) with the previous one (95 %).
2. b) Based on the case of Clara and Sergio, justify biologically why a person's decision not to get vaccinated is not just an individual choice regarding their own health, but directly endangers the most vulnerable members of the community.

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 blood groups are, why it is essential to know them before a transfusion, and which group can donate red blood cells to anyone.

In Spain, 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.

Explain what a transplant is and cite two organs or tissues that are frequently transplanted, indicating which health problem each one solves.

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.

Explain what bone marrow donation consists of, what type of patients it can cure, and why it is so difficult to find a compatible donor.

Irene suffers from severe kidney failure and her kidneys barely filter waste from her blood. Her brother Juan, who is completely healthy, offers to be a living kidney donor. However, the hospital spends weeks conducting exhaustive blood and immunological compatibility tests (leukocyte antigens) before authorizing the procedure.

1. a) Predict and explain what would happen at the cellular level in Irene's body if her brother's kidney were transplanted without prior verification of their antigen compatibility.
2. b) If the surgery is successful, how is it possible for Juan to continue leading a normal and healthy life with only one kidney? Justify how his body responds to maintain blood filtration and homeostasis.