The late switch from Ms Rousseff to Ms Silva may have been caused partly by a row about Brazil's abortion laws.

ECONOMIST: Brazil's presidential election

"You have to really be able to articulate the reason why you want to make the switch, " says Ms. Mannion.

WSJ: Contemplating a Career in Nonprofits?

To ease the seasonal swap, or to switch bags for the weekend, Ms. Botkier keeps her makeup in pouches.

WSJ: Tricks of the Trade: The Bag Makes the Woman

If 10% of these patients switch to Tysabri, it would mean an additional 30, 000 MS patients that Wall Street is not counting on.

FORBES: Loving Elan's Latest Comeback