I think this advert should be banned!!! In the dark ages before Domestos there were loads of germs which you built up an immunity against. Nowadays everything is so clean and sterile if one little germ escapes you die.....
Obviously the statement is tortological, but in advertising, it helps to punch home your message, and a one-syllable word which can be delivered with suitable power makes sure everyone is paying attention to the message.
As for the "99%" - advertisers are unable to say anything is one hundred per cent of anything because that cannot be proven, so it's against the advertising legislation.