The graph below shows the number of cases of measles that occurred in the world between 1980 and 2010 - Scottish Highers Human Biology - Question 11 - 2016

The vaccination rate during the period when there were 3-5 million cases was approximately 70%.

To calculate the percentage decrease:

1. Find the number of cases in 1995, which is around 1 million.

2. Find the number of cases in 2010, which is around 0.3 million.

3. Use the formula for percentage decrease:

   $ext{Percentage Decrease} = \frac{ ext{Old Value} - ext{New Value}}{ ext{Old Value}} \times 100$

   $\text{Percentage Decrease} = \frac{1 - 0.3}{1} \times 100 = 70\%$

In countries with established herd immunity, the majority of the population is vaccinated. This significantly reduces the overall presence of the measles virus, which means that individuals who are not vaccinated are less likely to come into contact with someone infected, thus providing them with some level of protection.

One reason could be malnutrition or poverty, which limits access to medical resources or vaccines, making it challenging to implement comprehensive vaccination programmes.

In 2010, the global population was 6900 million. If the vaccination rate was 70%, then the number of vaccinated individuals is:

$\text{Vaccinated} = 6900 \times 0.7 = 4830 \text{ million}$

Thus, the number of people who had not been vaccinated is:

$\text{Not Vaccinated} = 6900 - 4830 = 2070 \text{ million}$

The graph shows a clear decline in the number of measles cases over time, especially between the years 2005 and 2010, where a significant decrease occurred. If this trend continues, it suggests that with consistent vaccination efforts, measles could be eliminated by 2020. Specifically, if the rate of decrease remains constant, eventually there will be no cases of measles.