geneva studies show people with the coronavirus are most infectious just at the point when they first begin to feel unwell world health organization who experts said on tuesdaythis feature has made it so hard to control spread of the virus that causes covid19 disease but it can be done through rigorous testing and social distancing they saidit appears from very limited information we have right now that people have more virus in their body at or around the time that they develop symptoms so very early on maria van kerkhove a who epidemiologist and technical lead on the pandemic told a live session on social mediapreliminary studies from germany and the united states suggest that people with mild symptoms can be infectious for up to 89 days and it can be a lot longer for people who are more severely ill she saidearlier some disease experts questioned her statement on monday that transmission of covid19 by people with no symptoms is very rare saying this guidance could pose problems for governments as they seek to lift lockdownsvan kerkhove citing diseasemodelling studies clarified on tuesday that some people do not develop symptoms but can still infect otherssome estimates of around 40 percent of transmission may be due to asymptomatic cases but those are from models so i didnt include that in my answer yesterday but wanted to make sure that i made that clear she saiddr mike ryan whos top emergencies expert said that the novel coronavirus lodges in the upper respiratory tract making it easier to transmit by droplets than related viruses such as sars or mers which are in the lower tractnow as we look at covid19 we have an infectious pathogen that is present in the upper airway for which the viral loads are peaking at the time you are just beginning to get sick he saidthat means you could be in the restaurant feeling perfectly well and start to get a fever you are feeling ok you didnt think to stay home but thats the moment at which your viral load could be actually quite high he saidryan added and its because the disease can spread at that moment that the disease is so contagious thats why it spread around the world in such an uncontained way is because its hard to stop this virusbut some countries have shown that transmission can be brought down to an acceptable level or even to no level as new zealand had recently demonstrated he said