You can use newspapers to find Primary and Secondary sources
if you have questions about the difference between primary and secondary sources I am happy to answer them.
Message from your Librarian on Researching the Spanish Flu
I know you are going to start your search by googling "Spanish Flu" which is not wrong BUT please use the CRAAP Test before you start quoting facts from random websites!
Pay special attention to the first A(uthority) and the P(urpose) in CRAAP. The FIRST thing I do when I find an online source is find the "About" section. The About section should tell you who made the website (Authority) and why (Purpose); if you can't find this information move on to another source.
For example: Is this website someone's side hobby? If yes, the information could be great or the content is full of false facts; you won't know so find a better source. If the website is an official project with backing and funding from Universities and relevant government agencies then that is probably a credible source. Even safer does the online source have an editorial board vetting the information?
If you have questions about the credibility of an online source you found you can always ask me.
This Information Guide includes online sources I've pre-vetted (in the description I explain why I think the source is safe but please double-check) and this guide also includes databases with scholarly articles and newspapers.
Last tip - google "[insert term for Spanish Flu] archives " this will hopefully point you towards more scholarly collections online.
other names the Spanish Flue is known by:
The above online collection of Encyclopedias will provide short authoritative summaries on various subjects. I recommend starting your search in GVRL to bit size information from medical, social, and historic perspectives on your topic.