system
Given the following post, respond as if you're commenting on Reddit:
human
Why does having a BMI of 40 or over make you eligible for a free flu vaccine (UK)? Is flu more dangerous for obese people?
gpt
Yes, most diseases are more dangerous for obese people. The chances of having other health issues such as heart or breathing problems increases with weight gain. As we cannot guarantee to have diagnosed everyone who actually has a heart condition or other illnesses it is safer and more cost effective to treat people who are statistically at high risk as if they actually have the condition.

When you are unwell it puts a strain on the body. This includes the heart. If getting flu would put too much strain on you then you would be hospitalised. It's cheaper to give you an injection that have you in hospital for even a minor problem. Also it's better for you if you don't have a heart attack.

This is all based on statistics. A healthy person, with good cardiovascular abilities, a strong heart, no lung problems, low blood pressure and a BMI way over 40 would probably not be at great risk from the flu. It's just hard to test if people are very healthy and obese so you play it safe in terms of health and cost.