ARM 2: Coprimary outcome 2.incidence of any upper or lower community acquired respiratory viral infection (define as identification of respiratory viruses such as coronavirus other than SARS-CoV-2; influenza; parainfluenza; respiratory syncytial virus; rhinovirus; adenovirus; human metapneumovirus).Assessed using local standard of care testing (e.g. respiratory swabs; saliva and/or blood)[28 days from baseline];ARM 2: Coprimary outcome 1incidence of COVID-19 when Interferon alpha is given as post-exposure prophylaxis with a known positive contact or exposure with COVID-19. COVID-19 confirmed by qPCR from respiratory swab .[28 days from baseline]

ARM 2: Coprimary outcome 2.incidence of any upper or lower community acquired respiratory viral infection (define as identification of respiratory viruses such as coronavirus other than SARS-CoV-2; influenza; parainfluenza; respiratory syncytial virus; rhinovirus; adenovirus; human metapneumovirus).Assessed using local standard of care testing (e.g. respiratory swabs; saliva and/or blood)[28 days from baseline];ARM 2: Coprimary outcome 1incidence of COVID-19 when Interferon alpha is given as post-exposure prophylaxis with a known positive contact or exposure with COVID-19. COVID-19 confirmed by qPCR from respiratory swab .[28 days from baseline]