Each year there are at least five million people around the world who develop serious flu ( 流感 ) , and almost half a million deaths.When someone we know gets the flu virus , we expect them to be very careful not to pass it on to others.Doctors and nurses working with flu patients also need to protect themselves from the virus.But what is the best way to do this? This is the question that flu expert Professor Jonathan Van-Tam at Nottingham University is trying to answer.He wants to find out how flu is transmitted , so that he can stop doctors and nurses getting sick. Van-Tam explains their method , “ There are 41 volunteers in my experiment.Some healthy volunteers are made to get flu first.When they show symptoms ( 症状 ) , other volunteers , usually called recipients( 接受者 ) , enter the house.Everyone lives together in the small space for four days.Some of the recipients wear face masks , and wash their hands every 15 minutes , but some have no protection.In this way we can study who catches the flu and which ways of transmitting flu are important.During the four days when they are in contact with the virus , and for the ten days after that , the flu recipients are checked regularly. ” The experiment is not simple and it is very expensive.It is difficult to design correctly , and it is also difficult to plan and carry out.Just one study like this takes about 18 months to organize and needs hundreds of people working on it.But Van-Tam believes it is worth because the results will help to decide what type of protection is needed for people working in hospitals with large numbers of flu patients around the world.And perhaps it could reduce the number of deaths from flu each year.