how do you answer the question how do you do?

A: How do you do?
B: How do you do?

Is it okay to say;

A: How do you do?
B: Fine, you?

Here are some answers:

I'm fine, thank you. How are you?

I'm terribly sick right now. Please excuse me if I don't get too close or shake your hand. How are you?

I'm pleased to see you again. How are you?

Happy to meet you. How are you?

One of the first things I learned many years ago, when I started learning English was this:

The question 'How are you?' can be answered with the phrase 'Fine, thanks.'

The question 'How do you do you?' should always be answered with another 'How do you do?'

Just like Eliza Doolittle was taught in 'My Fair Lady'.

As Mr Micawber and Stormy have suggested, the traditional, and only correct, response to 'How do you do?' in Britain was 'How do you do?' I was taught at home and at school in the 1950s that this was the only correct exchange when one was first introduced to somebody; 'Pleased/Nice to meet you' was definitely infra dig, as was any attempt to 'answer' the formulaic 'How do you do?'