This article is good about why some people have side effects and some don't www.bbc.co.uk/news/health-56375307
But even two people the same age can have wildly different reactions to a vaccine.
"There is enormous genetic diversity in our immune systems, that's what underlies the difference," Prof Riley told Inside Health.
This diversity means some people's immune systems run a little bit hotter and are more prone to reacting aggressively.
Prof Riley said: "The people who, like yourself, go into full blown flu-like symptoms have rather overreacted to the whole thing.
"And it may be you're one of those people that always feels terribly ill if you have a cold or flu. I don't want to accuse you of having man-flu, but you may be one of those people."
Another factor that slightly increases the chance of side effects is having had a previous coronavirus infection, which can lead to an incredibly strong immune response after vaccination.
Do side effects mean I have more protection?
Selfishly, I had hoped that having side effects meant I had an incredibly strong immune response and there has been some evidence from previous vaccines that this would be the case.
"There are examples, like pandemic flu in 2009, where stronger side effects meant a strong immune response," said Prof Pollard.
But that is not the case with the Covid vaccine, everyone is getting roughly the same protection.
"It's fascinating, even though the elderly had few side effects, they had exactly the same immune response."