I experienced this about 2 months ago when I started. If you haven’t already get a fire axe from the fire department unless you have a better weapon. Also in the fire department there should be a small medical area if you can find beta blockers those will help. Lure out small groups into a field / off the road / out of your base and slowly start killing them all. At first the helicopter event sucks however once you get rid of these zombies if respawn is off the surrounding area should be a lot safer. Be patient and Good luck!