Figure 2
From: Prior immunity helps to explain wave-like behaviour of pandemic influenza in 1918-9
Observations over three waves. For each population there was information on N individuals, of whom N 1 reported symptoms in wave 1 and N 0 did not; in wave 2, N 12 had a repeat attack, while N 10 of those affected in wave one did not have a repeat attack; N 123 individuals reported symptoms in all three waves...;;etc. The total number reporting symptoms in wave 2 was N 12 + N 02 , while the total number for wave three was N 123 + N 103 + N 023 + N 003 . The observed numbers N 123 , N 120 , N 103 , N 100 , N 023 , N 020 , N 003 , N 000 for each population can be recovered from the proportions SAW, SA-, S-W, S- -, -AW, -A-, - -W, - - - shown in Table 1 by multiplication by the corresponding N.