Exercises: 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.

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.

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.

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.

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.

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.

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.

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.

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."

1. 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.
2. 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.