Indeed, Australia suffered "the worst flu season on record" for the majority of 2019 https://www.abc.net.au/news/2020-02-11/early-outbreaks-to-blame-for-worst-flu-season-on-record/11949320. It lasted eight months, despite 2019 being "one of the most successful vaccination years to date" (which dovetails with your speculation on whether vaccines are fueling disease outbreaks rather than curtailing them). So the outbreak of COVID in 2020 was not novel in Australia (the number of cases of COVID reported in 2020 was significantly less than those reported in 2019). These viruses have been circulating in the community for years. The CDC simply didn't receive the funding boost to label and promote until this decade.