The Alpha Incident

The Alpha Incident is a 1978 American film directed by Bill Rebane.

A space probe returns to Earth from Mars, carrying with it a deadly organism which has the lethal potential to destroy all life on Earth. Being transported across country by train, the microorganism is released when a nosy train employee inspects the cargo. This results in the entire train station being quarantined. Those trapped wait for the government to find a cure, while trying not to fall asleep because that is when this unseen killer strikes.

Source: Wikipedia