1918 Spanish Flu -Was it caused by an Experimental Meningititis Vaccine ?

Did the Influenza Virus Cause the 1918-1919 'Spanish Flu' Pandemic? Or was there a correlation with the experimental meningitis Vaccine given to US soldiers that year at Fort Riley, Kansas ?

https://historyofvaccines.org/blog/from-our-mailbag-did-the-influenza-virus-cause-the-1918-1919-influenza-pandemic