As of Monday, a generic version of Tamiflu is available in the US.

Unlisted generic drugmaker Alvogen, which developed the cut-price version with India’s Natco Pharma, said it expected the cheaper product to save the US healthcare system up to $500 million in the upcoming flu season.

Over the years, Tamiflu has provided Roche with occasional windfall profits as flu epidemics have led to spikes in demand, most notably during global H1N1 swine flu outbreak in 2009 when revenue from the drug hit almost $3 billion.

Since then sales have fallen back and Tamiflu is currently a relatively small component of Roche’s overall revenue, which reached $37 billion in the first nine months of 2016.

Roche faces bigger generic challenges starting next year, when the first so-called biosimilar versions of its injectable biotech cancer drugs are expected to reach the market in Europe.