The risk of being infected on an airplane cannot be excluded, but is currently considered to be low for an individual traveller. The risk of being infected in an airport is similar to that of any other place where many people gather. If it is established that a COVID-19 case has been on an airplane, other passengers who were at risk (as defined by how near they were seated to the infected passenger) will be contacted by public health authorities. Should you have questions about a flight you have taken, please contact your local health authority for advice.
The European Union Aviation Safety Agency (EASA) recommended measures to be taken by national authorities, such as thorough disinfecting and cleaning of aircraft after each flight serving high-risk destinations. EASA also recommended that airlines operating on all routes step up the frequency of cleaning, disinfect as a preventative measure and ensure full disinfection of any aircraft which has carried a passenger who was suspected or confirmed as being infected with COVID-19. Airport operators should similarly disinfect terminals regularly.
Because of how air circulates and is filtered (HEPA) on airplanes, most viruses and other germs do not spread easily. Although the risk of infection on an airplane is low, try to avoid contact with sick passengers and wash your hands often with soap and water for at least 20 seconds or use hand sanitizer that contains at least 60% alcohol.
Source: ECDC & CDC