Recent reports show that antibodies from Covid19 last only a month or two
Latest papers suggest 78 days but with a significant interpersonal variation. However this is not the same as immunity. The immune system stores the data and makes new antibodies if it re encounters the pathogen. Otherwise our blood would be solid, not liquid, from the millions of infections we encounter in our lives.
To date there are three cases of reinfection where we have enough data to demonstrate it is true. In all cases the second infection was asymptomatic or parsi symptomatic. ie the antibodies worked to avoid serious illness.
Sadly this doesnt help aviation. We will get a vaccine and together with the natural progression of infectious diseases plus increasing numbers of recovered cases life will return to normal. Until then fear in some countries, lockdown regulations and quarantine in some countries, and the issues of losing your flight money in some countries will work in the opposite direction.
My guess is we will have a vaccine by December, start mass vaccination in Q1 2021, and achieve vaccination / suppression / remission in europe, north america and australasia by Q3 or Q4. Governments need to concentrate financial support on transportation and hospitality in the meantime