Consider the following b4 deciding:-
a) if money is your main incentive, doing another UG degree e.g. in dentistry, or if you are flexible with subjects, accountancy or business studies, would be much better.
b) there is considerable and increasing demand for immunologists, particularly in view of the fact that pharmaceutical research is concentrating quite heavily on targetted therapy of diseases with specific antibodies against e.g. neoplastic cells, being a major part of this (employers that make a lot of money can afford to pay well, and pharmas make big money [I have worked in this sector, although I am a hopeless academic [dreadfully not money-minded]!).
c) I was offered an MSc in Medical Immunology at St Thomas' Hospital in London a short while ago (I won't tell you exactly when as you will put on your Usain Bolt shoes if I do!
); I decided not to take it up, mainly because I do not like lab work, and there was a lot of that in the course. If you like dealing with instruments (now very computerized) e.g. in immunohistochemistry, radioimmunoassay, etc. then this would be a positive point.
d) One other consideration is the nature of your UG degree (assuming you did one!) - if it was in an arts subject, you might find an MSc in a science/medical subject hard going.
e) Have you got any other offers for other science masters? Look at the pros/cons of these, too.
Weigh up your alternatives, if necessary mathematically as I do for making decisions in life, and make an informed decision.
Best of luck!