Given the antibody_data data frame, calculates the number that are alive (alive to be infected, that is) for each time in times
get_n_alive(antibody_data, times)the data frame of antibody data. See example_antibody_data
the vector of times to calculate number alive for
a vector giving the number alive in each time point
Other get_summary:
get_DOBs(),
get_n_alive_group()