Actor languages such as Erlang and Elixir have emerged as popular tools for designing reliable, fault-tolerant distributed applications, but communication patterns used by actors are often informally specified. Multiparty session types (MPSTs) are a type discipline for communication protocols: if a program typechecks according to its session type, then it is guaranteed to fulfil its role in a communication protocol, but the unidirectional communication mechanism used by actors makes it difficult to apply session types to actor languages directly. By combining a flow-sensitive effect system with an event-driven programming model, we show the first statically-typed session type system for actors that can participate in multiple sessions.