Re: "This is because, while an effective drug can save lives, it cannot significantly slow or prevent the spread of an outbreak."
Why couldn't prophylactic use of a hypothetically effective future EbolaCide2 stop and halt the spread of disease? If EbolaCide2 kills the virus and drops the viral load, it could possibly keep that person from shedding and spreading the virus to others. If others who came in contact, or anticipate possibly coming into contact with an infected person took EbolaCide2 before they became ill (and a single dose of EbolaCide2 could possibly be effective for several weeks), wouldn't that possibly prevent those people from developing illness - by killing the virus before it got a chance to replicate in the new host? How would this not halt the spread of disease (viral replication across hosts)? It's the same thing that vaccine mediated immunity does - helps the new host kill the viral infection so the virus doesn't replicate in the new host or in any other new hosts.
One might have to rely on quarantine of those exposed to a virus, as vaccination of someone in the early stage of viral infection is NOT expected to help that person out at all, right? Drugs would be much better for those people, as they could actually work up to several days after infection, or even several weeks before infection (as noted above).
Vaccines are good, but not everyone will take them, and not everyone *can* take them. Drugs are also needed, especially for viruses that mutate rapidly (like Ebola and influenza), if the drug is broad-spectrum and not affected by viral mutations - as the 'cides are expected to be.
Vaccines can prevent illness in those inoculated, but some drugs (like the 'cides) can also be used prophylactically like vaccines - for shorter periods of time. On the converse, vaccines can't cure any person suffering from an acute viral illness, as far as I know.
Obviously, it's usually easier to prevent a viral illness than to cure it, so a vaccine providing long-term immunity would hypothetically be preferred. On the other hand - SO many people need to be vaccinated it makes it harder.
Which is more important? I'm not sure that question can be or needs to be answered in general for all viruses as a group - as there are too many variables involved. Drugs can save lives now, but vaccines could possibly save more lives in the future (if the vaccine is safe enough, effective enough, if enough people take it, if the virus doesn't mutate enough, and if the virus is expected to be successful enough in the future to put a lot of people at risk).
