IGCSE Biology 0610: Active and Passive Immunity in a Vaccination Programme

A remote island community experiences an outbreak of whooping cough, a bacterial disease of the airways. Public health workers begin a mass vaccination programme for all children over two months old. Babies younger than two months are too young to be vaccinated, so health workers instead encourage mothers to breastfeed their babies, since the mothers themselves were vaccinated against whooping cough years earlier.

(a) State what is meant by: (i) active immunity (ii) passive immunity. [2]

(b) Explain how the vaccination programme is expected to give the older children long-term protection against whooping cough, referring to memory cells in your answer. [3]

(c) Explain how breastfeeding can give an unvaccinated young baby short-term protection against whooping cough, and state one way this protection differs from the protection gained by the vaccinated children. [3]

(d) Suggest why vaccinating a large proportion of the island's population, rather than only the children at greatest risk, helps to control the spread of whooping cough for the whole community, including people who cannot be vaccinated. [2]

Part (a): Defining active and passive immunity

(i) Active immunity: defence against a pathogen by the body making its own antibodies.

(ii) Passive immunity: short-term defence against a pathogen by antibodies acquired from another individual, rather than made by the body itself.

Part (b): Long-term protection for the vaccinated children

The vaccine introduces a weakened form of the whooping cough bacterium, or its antigens, into each child’s body. These antigens stimulate the children’s own lymphocytes to produce antibodies that fit the bacterium’s antigens.

At the same time, memory cells are produced. These remain in the body for a long time after the initial antibodies have broken down. If a vaccinated child later meets the real whooping cough bacterium, the memory cells allow the body to recognise it and produce the matching antibodies much faster and in much greater numbers than the first time. This rapid, strong response is what protects the child from becoming ill, and is why vaccination gives long-term protection.

Part (c): Short-term protection for breastfed babies

The mothers were vaccinated against whooping cough years earlier, so their blood contains antibodies against the bacterium. Some of these ready-made antibodies pass from the mother’s blood into her breast milk, and from there into the baby’s body during breastfeeding. These antibodies can act against the whooping cough bacterium, giving the baby protection even though the baby’s own immune system has not been involved at all.

This protection differs from the vaccinated children’s protection in an important way: because the baby’s own lymphocytes are never stimulated, no memory cells are produced in the baby. Once the mother’s antibodies are gradually broken down, the baby’s protection disappears, whereas the vaccinated children keep their memory cells and stay protected for the long term.

Part (d): Vaccinating a large proportion of the population

Whooping cough can only keep spreading through the community if there is a steady supply of people who can become infected and pass the bacterium on to others. If a large proportion of the population is vaccinated, most of these people cannot become infected (or only mildly so), which sharply reduces the total number of people carrying and spreading the bacterium at any time.

With far fewer infected people in the community, the chance of the bacterium ever reaching an unvaccinated person, such as a very young baby, becomes much lower. In this way, vaccinating a large share of the population protects even those who cannot be vaccinated themselves, as well as those who are.

Final answers

(a) (i) Active immunity: the body makes its own antibodies. (ii) Passive immunity: short-term protection from antibodies made by another individual.
(b) Antigens stimulate lymphocytes to produce antibodies, and memory cells are produced, giving a fast, strong response (and so long-term protection) if the bacterium is met again.
(c) Ready-made antibodies pass from mother to baby in breast milk, giving short-term protection; unlike the vaccinated children, no memory cells are produced in the baby.
(d) Vaccinating most of the population sharply reduces the number of infected people, lowering the chance the bacterium reaches those who cannot be vaccinated.