Swiss authorities issued Thursday a health alert about a flight from Tel-Aviv, warning passengers they might have been infected with measles from another traveller.
The public health office said the alert applied to El Al flight 347 to Zurich on Tuesday morning which connected with Swiss International Airlines flight 2806 to Geneva.
The ill passenger was on both flights.
"Measles transmission to unvaccinated passengers who have not contracted measles before cannot be ruled out," a statement from the health office said.
Switzerland has been in the grip of a measles epidemic since November 2006 because of relatively low vaccination rates that have made it the most infected country in Europe, according to a study.
Some 3,400 cases have been declared to authorities since the epidemic started, including 250 people who have had to be treated in hospital, according to the public health office.
A young girl from neighbouring France died in a Geneva hospital last month after contracting measles.
Some 27 percent of 12,132 cases recorded in 32 European countries in 2006 and 2007 came from Switzerland, the highest proportion, according to study published by the British medical journal The Lancet in January.
The epidemic has sparked a debate about making the vaccination against the virus compulsory in Switzerland.
Last year, the World Health Organization advised foreigners who were attending the Euro 2008 matches in Austria and Switzerland to make sure they were vaccinated against measles, to avoid spreading the disease worldwide.