Moderna shares fell to an almost three-year low amid concerns about COVID-19 vaccine demand. The company reiterated its full-year guidance of $6-8 billion in sales but said it was too early to predict exact demand. The update came after Pfizer, Moderna's competitor, cut its outlook "solely due to COVID products" and lack of demand for COVID vaccines and treatments. Moderna noted it will have better visibility about the expected U.S. vaccine market size by the end of October and will provide an update during its November 2nd earnings call. Moderna shares fell over 6% on Monday.