We are flying to Malawi with Kenya Airways, which means a transit through Nairobi. We won't be leaving the airport, so does this mean that we won't need a Yellow Fever jab? - Jason Burnham, Stoke on Trent

Sunday times travel expert Richard Green writes: Yellow Fever isn't present in Malawi, but it is in a part of the world that has the right conditions for the disease to take hold, were it introduced.

So if you are flying to Malawi from a country without endemic Yellow Fever ­ like the UK or Europe, or on one-stop flights via South Africa, you won't need a vaccination.

However, if you pass through a country where Yellow Fever is present, like nearby Kenya or Tanzania, you will need proof of vaccination. You can do this by using an internationally recognized certificate, which you'll get automatically wherever you get your jab from, as set up by the World Health Organization (WHO, www.who.int). Note that you must have the jab at least 10 days before you travel, but the good news is that it is then valid for 10 years after that.

The disease principally affects humans and monkeys, and is transmitted via the bite of Aedes mosquitoes, found in tropical areas of Africa and South America. There is a good map at http://www.fitfortravel.scot.nhs.uk/advice/diseases/yellowfever.htm.

The Hospital for Tropical Diseases has a Travellers Heathline Advisory Service (0207 950 7799, www.thehtd.org) for pre-travel advice and how to avoid illness whilst travelling. Also look at the good travel health resources at www.travelhealth.co.uk and www.fitfortravel.scot.nhs.uk.

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