The health protection agency gives some good advice here: http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/SeasonalInfluenza/InformationForThePublic/influsw15vaccinationandpregnancyFAQ/ When you're pregnant the part of your immune system that fights viruses is weakened. This is unrelated to how healthy you are pre-, or during, pregnancy, or whether you've successfully fought viruses before; it's essentially a side effect of your immune system not fighting the baby inside you (50% of which is genetically different to you). As a result, pregnant women are particularly susceptible to the H1N1 virus, which is one of the strains of 'flu virus doing the rounds this year, and are more likely to get severe complications such as pneumonia. I know all this because I'm an obstetrician and gynaecologist. 2 years ago, during the epidemic, I saw a previously fit and healthy pregnant woman tragically die from complications from H1N1. Her baby, which we'd had to deliver extremely prematurely, in an attempt to save her life, also died. Because of effective vaccination programmes, we often forget, in this day and age, that viruses can be deadly. I am currently pregnant, and was first in the queue for both the 'flu, and later, the pertussis vaccines. I really urge all pregnant women to do the same.