Very difficult decision to make. Pregnant women are uniquely vulnerable ( particularly in second and third trimesters) due the suppression of their natural immune system to avoid damaging the foetus.
Health Emergency - Information on Vulnerable Groups
It would appear however that antivirals are not contra-indicated in the event of infection -which is good.
Health Emergency - Antiviral recommendations
There are however very few facilities ( effectively none in the event of a large outbreak) in the UK for the specialist blood re-oxygenation treatment necessary in acute cases --- witness the Scottish Woman sent to Scandinavia for treatment. This might have implications for foetal oxygen deprivation.
also some re-assurance on vaccine safety:- http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/national-vaccination-program/$file/thiomersal.pdf
You will see from these links I am citing
Australian references. The country has a sophisticated medical system and a reasonably open system of government reporting. They have already experienced a Swine Flu epidemic and a vaccination program so I would predict the best clinical
experience/outcomes as opposed to prediction is to found there. I hope this helps a little Ollie with you and your partners' difficult decision.