Oops. Due to an incident involving some old dilithium crystals and a dodgy antimatter containment field generator I got cheap, there appears to have been a small explosion.
This has blown you through a wormhole in the space-time continum.

The year is now 1937 and you're in Max Theiler's lab in South Africa.

Max Theiler (for it is he):

"Since Reed's original work, we've found out a lot more about yellow fever. For one thing, we now know that the disease is caused by a virus, something which followed from Reed's eventual demonstration that this was a filterable agent.

Also, we discovered that we could transmit the virus to a variety of animals and animal cells in culture. We've been growing a strain of the virus we call 17D in chick embryo cells for a number of years. We think that this could be the basis of a useful vaccine to prevent yellow fever.

Care to guess how we made the vaccine?

• By growing the virus in chick cells and inactivating it with formalin

• By attenuating the 17D strain after many sequential passages in chick cells

• By cloning the virus and expressing it in E. coli