Figure 3.

Probability distribution of k animals with HI ≥ 8. Probability distribution of 0–10 animals per group with HI ≥ 8. (a) In groups where the vaccine and challenge strains have an antigenic distance of 0 (i.e. homologous groups H5N1 R65 vaccinated/H5N1 R65 challenged and H5N1 t/T vaccinated/H5N1 t/T challenged). (b) In groups where the vaccine and challenge strains have an antigenic distance of 9.83 (2^3.30) HIU (i.e. R65-P30 vaccinated/H5N1 R65 challenged). (c) In groups where the vaccine and challenge strains have an antigenic distance of 80.88 (2^6.34) HIU (i.e. H5N2 vaccinated/H5N1 R65 challenged). (d) In groups where the vaccine and challenge strains have an antigenic distance of 4.49 (2^2.17) HIU (i.e. t/T-P42 vaccinated/H5N1 R65 challenged). The blue vertical line separates the scenarios where R > 1 and R < 1, according to the probability distribution of the number of animals with HI ≥ 8 against the challenge strain. Blue arrows indicate the experimentally observed number of animals with HI ≥ 8 against the challenge strain for each vaccine group.