This is the 11189th most frequent Russian word.
гриппе
The Russian word "гриппе" is the prepositional case of "грипп," meaning "flu" in English.
The word "гриппом" is in instrumental case here, indicating the cause of the illness.
Я болею гриппом.
I am sick with the flu.
Here, "гриппа" is in genitive case, describing the time of having the flu.
Во время гриппа следует отдыхать.
During flu, one should rest.
In this context, "гриппа" is also in genitive case, indicating what the vaccine is against.