Fig. 4

Near-future outcomes given past immunity. a Younger population, near-future attack rate; b Older population, near-future attack-rate (the diagonal line represents where past and near-future attack rates are equal); c Younger population, near-future deaths; d Older population, near-future deaths. Note that past attack rate is calculated between \(t\in \left( 0,450\right)\). Past attack rate is dependent on transmission potential, which is different for various simulations, reflecting different populations’ intrinsic transmission. Near-future attack rate and near-future deaths are calculated between \(t\in \left[ 450,650\right)\). Note that we have only included simulation results in which the past attack rate is between 20% and 80%