Question: We have the registry of subjects who are vaccinated against the flu in a specific region and campaign, which includes information at the time of vaccination on pathological history, age, sex and type of vaccine. For the same subjects we also have the registry with hospital discharge diagnoses, which occurred after the date of vaccination, and there is a personal identifier common to both registers. Indicate which of these studies would be possible to carry out using only the aforementioned sources of information: 
 Options:  <1> An analytical cohort study to determine if vaccination increases the risk of developing Guillain-Barré syndrome in the first 16 weeks after influenza vaccination. <2> A descriptive analysis to estimate the incidence of acute myocardial infarction in the first 16 weeks after anti-flu vaccination. <3> A descriptive analysis to estimate the incidence of fever in the first week after the influenza vaccination. <4> A clinical trial that compares the risk of serious post-vaccine reactions (involving hospital admission) with two of the types of influenza vaccines used in that campaign. <5> A case-control study to determine if vaccination increases the risk of developing an acute myocardial infarction.
2