// question: 0  name: Switch category to $module$/Default for Step 3.6 Calculating vaccine efficacy and herd immunity threshold - Quiz
$CATEGORY: $module$/Default for Step 3.6 Calculating vaccine efficacy and herd immunity threshold - Quiz


// question: 282  name: Q1 Assume that Ebola has a basic case reproduction number (R0) of 2.
::Q1 Assume that Ebola has a basic case reproduction number (R0) of 2.::[html]<p>Assume that Ebola has a basic case reproduction number (R<sub>0</sub>) of 2. What percentage of the population must be immune in order to reach the herd immunity threshold?</p>{
	~<p>67%</p>#<p>Remember the formula for herd immunity threshold\:</p>\n<p>Herd immunity threshold \= (R<sub><span>0</span></sub>-1)/R<sub><span>0</span></sub></p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
	=<p>50%</p>#<p><span>The formula for herd immunity threshold \= (R</span><sub><span>0</span></sub><span>-1)/R</span><sub><span>0</span></sub><span>. As such, in this case herd immunity threshold\: (2-1)/2\= 0.50 \= 50%</span></p>
	~<p>33%</p>#<p>Remember the formula for herd immunity threshold\:</p>\n<p>Herd immunity threshold \= (R0-1)/R0</p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
}


// question: 283  name: Q2 Vaccines are not 100% effective.
::Q2 Vaccines are not 100% effective.::[html]<p>Vaccines are not 100% effective. The percentage of the population that needs to be vaccinated to reach the herd immunity threshold (the vaccine coverage) depends on the vaccine efficacy.</p>\n<p>Assume a vaccine for Ebola is available with an efficacy of 75%, and that the R0 for Ebola is 2 (as in the previous example).</p>\n<p>What proportion of individuals must be vaccinated in order to reach the herd immunity threshold? (Hint\: the HIT has already been calculated and is 50%.)</p>{
	=<p>67%</p>#<p><span>Required vaccine coverage \= herd immunity threshold / vaccine efficacy. Therefore, the proportion that would need to be vaccinated to get R\=1 \= 50% / 75% \= 0.667 or 67%.</span></p>
	~<p>50%</p>#<p>Remember that the required vaccine coverage \= herd immunity threshold / vaccine efficacy.</p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
	~<p>33%</p>#<p>Remember that the required vaccine coverage \= herd immunity threshold / vaccine efficacy.</p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
}


// question: 289  name: Q3 If the R0 for Ebola was 1.3 rather than 2 (e.g. in a totally susceptible population where procedures
::Q3 If the R0 for Ebola was 1.3 rather than 2 (e.g. in a totally susceptible population where procedures::[html]<p><span>If the R</span><sub><span>0</span></sub><span> for Ebola was 1.3 rather than 2 (e.g. in a totally susceptible population where procedures for contact tracing and isolation were already in place), which of the following is true, compared to the scenario in Q2</span></p>{
	~<p><span>You would need to vaccinate more people to reach the herd immunity threshold.</span></p>#<p>Remember the herd immunity threshold is R<span>0</span>-1/R<span>0</span>. If the herd immunity threshold is lower you would need to vaccinate fewer people.</p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
	=<p><span>For the same vaccine coverage a vaccine with lower efficacy could be used to reach the herd immunity threshold</span></p>#<p><span>Remember the herd immunity threshold is R</span><sub><span>0</span></sub><span>-1/R</span><sub><span>0</span></sub><span>, so is now (1.3-1)/1.3 \= 23%. With a vaccine coverage of 67% (as in Q2) even a vaccine with quite low efficacy could be helpful.</span></p>
	~<p><span>This would make no difference to the proportion of the population that would need to be vaccinated to reach the herd immunity threshold</span></p>#<p>Remember the herd immunity threshold is R<span>0</span>-1/R<span>0</span>. If the herd immunity threshold is lower you would need to vaccinate fewer people.</p>\n<p>You may find <a href\="http\://open.lshtm.ac.uk/mod/page/view.php?id\=276">3.5 How would vaccines help?</a> useful.</p>
}