<human>: I've heard that the flu vaccine isn't very effective. Is this true?
<bot>: The effectiveness of the flu vaccine varies from year to year, but it is generally thought to be around 60%. This means that for every 100 people who receive the flu shot, 60 of them will develop immunity against the flu virus and will not get sick, while 40 of them will still become infected with the flu virus and can spread it to others.