The 2016 video cited by The Guardian and ABC News proves that no such incident took place where Trump flees after a man shouts 'coronavirus'.
The description of the original video cited by The Guardian and ABC News articles says that a protester tried to rush to the stage at Trump's rally held in Dayton, Ohio on 12 March 2016. The secret service officers had to form a protective cordon around Donald Trump after that.
The viral video has been manipulated to add a man next to Trump at the podium who yells 'coronavirus' and backs away, followed by the secret service forming a protective cordon. Therefore it is proved that the viral video is fake.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.