Explain how vaccinations can protect a population against infectious diseases such as pertussis (whooping cough). [3][3][3].
The graph below shows the number of reported pertussis cases per year in a country from 1950 to 2010.
In 1957, a national vaccination program against pertussis was first introduced for infants. Since then, two subsequent significant events occurred that affected the number of pertussis cases.
Use the graph to suggest a year when each event occurred. Give one reason for your choice of year for each event.
(i) A safety concern report was published in the media, leading to public anxiety about the whole-cell pertussis vaccine.
- Year: _______
- Reason: _____________________________________________________ [2][2][2].
(ii) A newer, safer acellular vaccine with fewer side effects was introduced, restoring public trust.
- Year: _______
- Reason: _____________________________________________________ [2][2][2].
A study looked at how helper T-cells and memory lymphocytes for other pathogens in the body are affected following infection with a specific respiratory virus (Virus X).
The study compared three groups of children six weeks after infection:
- children who did not have Virus X
- children who recovered from mild cases of Virus X
- children who recovered from severe cases of Virus X
The study measured the percentage of pre-existing memory T-cells remaining in the body. The results are shown in the dot plot below:
Most people recover from Virus X but are much more likely to fall ill with other, unrelated diseases during the months following recovery.
How do the findings shown in this diagram explain this after-effect of infection with Virus X? [2][2][2].