French to English Medical Medical (general) Forms of MS

First of all, I would like to say that I have checked in the Kudoz glossaries/answers for this term.

Here is how it appears in my text:

Switch pour efficacité - suite à 1 poussée

(from a market survey about MS drugs currently being used as 1st and 2nd (and later) line treatments). The switch is obviously referring to switching from one drug to another for whatever reason (e.g. here, efficacy). Now, I am pretty sure that it means 'flare-up' or 'attack' or 'bout' of MS, but as some of these drugs are administered in the form of an injection, I had a very small but nagging suspicion that it might be referring to the actual injection (in terms of the thrust of the injection into the skin, etc.). I would be most grateful if a medical expert could clear up that doubt for me!

Thanks in advance.

:)