1) Type A viruses (see under individual subtypes)

2) Type B viruses (there are no subtypes of influenza B virus)

3) A subtype H1N1

4) A subtype H2N2

5) A subtype H3N2

6) Other subtypes (other than those found in humans, above)

7) Reassortants

8) Mutants

9) Human viruses (including reassortants with wt-like HA and NA combinations)

10) Animal or avian viruses

11) Animal virus - human virus hybrids

12) Antigenic (HA/NA) hybrids

12a) Human NA-specific antigenic hybrids (e.g. H7N2)

12b) Human HA-specific antigenic hybrids (e.g., H3N7)

13) High yield (hy) reassortants (including vaccine viruses and vaccine candidate viruses)

14) Mouse lung adapted

15) Potentially neurovirulent in mice (NWS or WSN ancestry)

16) Vaccine candidates (hy reassortants of antigenically drifted and potentially important viruses)

17) Vaccine viruses (used in commercial or clinical trial vaccines)

18) Pandemic vaccine candidates (including hy reassortants and mutants) These viruses include animal strains not yet associated with epidemic disease, e.g., H5N1, H7N7, and a previous pandemic human subtype (H2N2) no longer epidemic or endemic in humans.