As Robert said and I know full well being a nurse practitioner, there is no way that you'll be able to drag yourself to church if you truly have the flu. It puts you down!! People confuse a "bad cold" or bronchitis with the flu. Flu keeps you out of circulation for days.
As others already said, cover when you sneeze and cough, sit away from others, don't shake hands, wash your hands often!!! and call or visit your primary care provider for guidance on your symptoms and what you have.
Ask your priest for guidance on whether it's a sin when you have a slight illness.
If it's a flu and you really can't get out of bed anyway... I was always told that God understands if you can't make it to mass due to severe illness, but you still need to devote some special time to God. You can try doing a Eucharistic adoration from home with the site savior.org. They have a webcam which always shows the Eucharist in exposition.
(From the first week of Jan through APRIL)! They should have stayed Home!
If I am terribly sick I watch The Sunday Catholic mass on:
" Heart of the Nation" out of Milwaukee WI., airing on ION TV ( early Sunday morning).
The email is: Mail@ HeartoftheNation.org
Hopefully there is a Catholic mass somewhere in everyone's viewing area!
*Find out before winter sets in, just in case!
Catholic apologist Jimmy Akin wrote a post on the issue several years ago.
One winter, we had a priest who mentioned during his sermon that an elderly parishioner called the rectory all upset. There had been a bad winter storm that left a lot of ice and she was nervous about falling on her way to mass. The priest said it was okay to stay home under those circumstances. People can use common sense.
Everything isn't a sin.