Commercial aviation was in its infancy in 1919. No commercial airliner had the range for trans-atlantic service in 1919. The US Navy did fly one squadron of seaplanes from Puerto Rico to the Azores to Europe in 1918. The RAF did fly one bomber from Ireland to Newfoundland in 1919. However, neither one of these flights spread the Spanish Flu, since it was already in the United States, before these flights took place.
Source: "Aviation: The Smithsonian Centennial History of Powered Flight."