Reference no: EM133206297

Question

Consider the following scenario in early 2020. Fred is a supermarket worker. He lives and works in a Sydney suburb where COVID-19 cases are increasing rapidly due to the current Delta variant outbreak. There has been a significant number of community transmitted infections in the suburb. Fred is concerned about the current COVID-19 situation, especially?since?he needs to work in the local supermarket five days a week. 

Fred wants to get vaccinated sooner rather than later. He understands that while vaccination does not completely eliminate the risk for COVID-19 infection, it will help protect people by significantly reducing the chances of infection, hospitalisation, and death. Fred hears that the effectiveness of the different brands of vaccines is similar - recent statistics show that fully vaccinated people (with any brand of vaccine for COVID -19, e.g.,?AstraZeneca, Pfizer, and?Moderna) only have 1/8 chances to have an infection and 1/25 chances to die from COVID-19 infection?compared to?those who are unvaccinated. 

However, Fred hears that different brands of vaccines may have different side effects (or adverse effects). Fred does not worry about mild adverse effects (e.g., redness or swelling at the injection site, headaches, and fever). He is only concerned about the very rare but serious risks that could lead to death. 

As Australia currently has a very low vaccination rate, Fred searches for COVID-19 vaccine side effects statistics in other countries where more doses of COVID-19 vaccines have been administered. Fred notices that the European Medicines Agency (EMA)'s safety committee reported in April that unusual blood clots should be listed as a very rare side effect of the?AstraZeneca?vaccine for COVID-19. The committee found 18 fatal cases reported in Europe, where around 25 million people had received the?AstraZeneca?vaccine. The EMA's analysis also found that the?Moderna?vaccine for COVID-19 could also have some extremely rare but serious adverse effects (e.g.,myocarditis and pericarditis) that could lead to death. Five deaths were reported out of 20 million people who received the?Moderna?vaccine. 

Based on these statistics, Fred prefers the?Moderna?vaccine to the?AstraZeneca?vaccine (note: he is not eligible to receive the?Pfizer?vaccine). However, while the?AstraZeneca?vaccine is currently available in Australia, the first 1 million doses of the?Moderna?vaccine are not currently available and are expected to arrive in Australia next month. 

The current COVID-19 situation in Fred's suburb is rapidly deteriorating. Fred believes that if he waited for a month for the?Moderna?vaccine, there would be a 5% chance that he would get infected with COVID-19 before he gets vaccinated (given the nature of his supermarket job). Fred's family doctor advises him that the risk of death for people in his age group after contracting COVID-19 is around 2%. 

Fred's objective is to minimise the likelihood of death. Fred wants to know if he should get the?AstraZeneca?vaccine today or wait for the?Moderna?vaccine. [Assumption: A person only needs to receive one shot to get fully vaccinated. If Fred got infected while waiting for the?Moderna?vaccine, he would not be eligible to receive the vaccine.] 

a) Develop a decision tree for Fred showing full details. Assumptions need to be stated clearly. Show your workings (e.g., include a Chance Table and Consequence Table), which allow the marker to award you partial marks appropriately.

b) Solve the decision tree by folding back the tree. Clearly show your calculations. Describe in words the optimal decision strategy.

c) Do you think Fred's decision model in a) is a requisite decision model? What other decision elements would you consider if you were Fred? Discuss.