Date: 201906
Local time of day: 1201-1800
Location: ZMA.ARTCC, FL
Flight conditions: VMC
Weather elements / visibility: Thunderstorm; Turbulence
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZMA
ATC / advisory: Center ZMA
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Speed All Types; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action; Flight Crew Regained Aircraft Control
Contributing factors: Procedure; Weather
Primary problem: Weather

Narrative: I was the FO (First Officer). Approaching overhead MIA; we experienced severe turbulence; resulting in over speed; stick shaker; large height deviations and at least four passengers reported injured. Flight continued with normal landing and disembarkation in ZZZ1.During the initial briefing in ZZZ; I questioned why we were taking a route through south Florida weather when the route [over water] was in the clear. A call to Dispatch was made. The Dispatcher suggested this route because of 2+ hour (traffic related) delays crossing the Gulf of Mexico; reviewed the weather; and made a convincing case that the filed route was safe. Indeed; the filed route was adequate; as long as you could stay clear of all clouds.At XA08z; we were in cruise approaching overhead MIA at FL350; M.77. The Captain and I were discussing our deviation plan around some weather ahead. A deviation decision was reached; but at the moment I was about to call for weather deviation; we were given handoff to a different ZMA sector. I attempted checking into the new ZMA (132.2) with 'weather deviation required'. ZMA did not acknowledge us; but continued directing other traffic. We started a weather contingency turn to avoid weather. During the turn; we clipped the corner of said clouds and experienced +300 ft climb; followed by a descent to 34;200 ft. Also experienced both an over speed and stick shaker before severe turbulence subsided. Event ended; and we returned to assigned altitude. I attempted to report our deviation; as well as our severe turbulence encounter; again with no acknowledgment from ZMA. At XA13z; we were given a new ZMA frequency. I switched to the new ZMA frequency; reported our deviations; and received the expected revised clearance.After the severe turbulence: We were in or near cloud tops and experiencing continuous light chop; but still feeling the sting of the previous event; so we had everyone remain seated until we were sure that we were out of the weather. During this period before the 'flight attendants; check in' call was made; there were many discussions by interphone between the captain and the purser regarding cabin status and passenger injuries. Once the seatbelt sign was off; the initial reported injuries were documented by the Purser. Chief Purser came to the cockpit and reviewed the reported injuries with the Captain. I assumed PF (Pilot Flying) duties and also manned VHF 1 during this period; so I didn't monitor their discussions or the VHF 2 calls that took place; but I did relay the cabin report of a fourth injured passenger to the purser during this time. Ultimately; the reported injuries were such that it was decided that medical personnel would attend to the injured after normal landing in ZZZ1.No help from ATC: Received handoff to a new Miami Center (132.2) sector at XA08z; just as we were about to request left deviations to avoid some weather ahead. New Controller never acknowledged us checking on to his frequency; never acknowledged 'weather deviations required'; and never acknowledged 'severe turbulence' reported after the event. We were able to hear normal (congested frequency) two way communications with all aircraft on 132.2 throughout our time with this particular controller; and we did get the normal handoff to the next ZMA Controller at XA13z.Success: '...be seated immediately... ' works. The flight attendants were all working in the galleys at the time and took their jump seats just before the worst of the turbulence began. No crew injuries were reported.Surprise: This particular cell was a surprise to both the captain and I with regards to intensity. We had both a visual and radar picture before reaching the weather. With our turn; I anticipated we would perhaps have light chop at most. That was not our case.Hindsight is 20/20: Going forward; I will not spend as much time waiting for ATC to authorize a weather deviation if I'm not getting acknowledgment. We waited to deviate until we felt couldn't wait any more; but ultimately; the turn was insufficient to avoid weather completely. That being said; we were both surprised by the strength of what I thought would be just light chop.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported encountering severe turbulence associated with a weather system; resulting in several non-crew injuries in the passenger cabin.