Converts a data frame of individual sampling times to give the index of the last infection that individual could have had (as we can't observe anything after the last observation)
create_sample_mask(antibody_data, possible_exposure_times)the data frame of antibody data. See example_antibody_data
the vector of times that individuals can be infected
a vector giving the last index of possible_exposure_times that an individual can be infected
Other create_masks:
create_age_mask()