Important Info on Spanish Flu
Like the Spanish flu virus, H5N1 is an avian virus, although a distantly related one. The evolutionary path that led to pandemic emergence of the Spanish flu is entirely unknown, but it appears to be different in many respects from the current situation with H5N1.
There is no historical data, either in 1918 or in any other pandemic, for establishing that a pandemic "precursor" virus caused a highly pathogenic outbreak in domestic poultry, and no highly pathogenic avian influenza (HPAI) virus, including H5N1 and a number of others, has ever been known to cause a major human epidemic, let alone a pandemic.
Even with modern antiviral and antibacterial drugs, vaccines, and prevention knowledge, the return of a pandemic virus equivalent in pathogenicity to the Spanish flu would likely kill more than 100 million people worldwide. A pandemic virus with the (alleged) pathogenic potential of some recent H5N1 outbreaks could cause substantially more deaths.
It is impossible to predict with certainly, but the probability of the Spanish flu virus re-emerging from a natural source appears to be remote. Influenza experts believe that a pandemic is most likely to be caused by an influenza subtype to which there is little, or no, preexisting immunity in the human population. There is evidence that some residual immunity to the Spanish flu virus, or a similar virus, is present in at least a portion of the human population. Since contemporary H1N1 viruses circulate widely and the current annual influenza vaccines contain an H1N1 component, a 1918-like H1N1 virus would not fit the current criteria for a new pandemic strain.
Prevention and Treatment of the Spanish Flu
Two types of antiviral drugs, rimantadine (Flumadine®) and oseltamivir (Tamiflu®), have been shown to be effective against influenza viruses similar to the 1918 flu virus. Vaccines containing the Spanish flu HA or other subtype H1 HA proteins were effective in protecting mice against the Spanish flu virus. In fact, the current influenza vaccine also provided some level of protection against the Spanish flu virus in mice.