Six months....impossible, page-151

Yeah, it's because they mainly test sick people and those who have been in contact with them.

For every positive test there may be a multiple of asymptomatic carriers spreading pathogens who have no reason to get tested because they haven't lost their sense of taste and smell, don't have a cough.
Don't find breathing difficult and so on.
They go about their daily business infecting others and can lead to untraceable cases where people are sick enough to get tested.
The untraceable ones are those that the boffins worry about.

If you were a modeller what figure would you take a stab at?