diff --git a/src/idmlaser_cholera/cholera.py b/src/idmlaser_cholera/cholera.py
index ba40a57..361e09f 100644
--- a/src/idmlaser_cholera/cholera.py
+++ b/src/idmlaser_cholera/cholera.py
@@ -120,7 +120,6 @@ class Model:
 from idmlaser_cholera.mods import init_prev
 from idmlaser_cholera.mods import transmission
 from idmlaser_cholera.mods import intrahost
-from idmlaser_cholera.mods import maternal_immunity as mi
 from idmlaser_cholera.mods import ri
 from idmlaser_cholera.mods import sia
 from idmlaser_cholera.mods import fertility
@@ -275,7 +274,7 @@ def check_for_cached():
     #intrahost.step2, # type: ignore
     transmission.step, # type: ignore
     #ri.step, # type: ignore
-    mi.step, # type: ignore
+    immunity.step, # type: ignore
     #sia.step, # type: ignore 
 ]
 
@@ -292,7 +291,7 @@ def check_for_cached():
 
     """
     #"""
-    if tick == 40:
+    if tick == 40: # outbreak/seeding
         init_prev.init( model )
     #"""
     metrics = [tick]
diff --git a/src/idmlaser_cholera/mods/immunity.py b/src/idmlaser_cholera/mods/immunity.py
index 2d3cd2a..5ae3173 100644
--- a/src/idmlaser_cholera/mods/immunity.py
+++ b/src/idmlaser_cholera/mods/immunity.py
@@ -1,6 +1,11 @@
 import numpy as np
 import numba as nb
 
+global use_nb
+use_nb = True
+global lib
+lib = None
+
 # initialize susceptibility based on age
 @nb.njit((nb.uint32, nb.int32[:], nb.uint8[:], nb.uint16[:]), parallel=True)
 def initialize_susceptibility(count, dob, susceptibility, susceptibility_timer):
@@ -20,4 +25,67 @@ def initialize_susceptibility(count, dob, susceptibility, susceptibility_timer):
     return
 
 def init( model ):
-    return initialize_susceptibility( model.population.count, model.population.dob, model.population.susceptibility, model.population.susceptibility_timer )
+    initialize_susceptibility( model.population.count, model.population.dob, model.population.susceptibility, model.population.susceptibility_timer )
+    try:
+        # Load the shared library
+        shared_lib_path = resource_filename('idmlaser_cholera', 'mods/libmi.so')
+        lib = ctypes.CDLL(shared_lib_path)
+
+        # Define the function prototype
+        lib.update_susceptibility_based_on_sus_timer.argtypes = [
+            ctypes.c_int32,
+            np.ctypeslib.ndpointer(dtype=np.uint16, ndim=1, flags='C_CONTIGUOUS'), # susceptibility_timer
+            np.ctypeslib.ndpointer(dtype=np.uint8, ndim=1, flags='C_CONTIGUOUS'), # susceptibility
+        ]
+            
+        lib.update_susceptibility_based_on_sus_timer.restype = None
+
+        lib.update_susceptibility_timer_strided_shards.argtypes = [
+            ctypes.c_int32,
+            np.ctypeslib.ndpointer(dtype=np.uint16, ndim=1, flags='C_CONTIGUOUS'), # susceptibility_timer
+            np.ctypeslib.ndpointer(dtype=np.uint8, ndim=1, flags='C_CONTIGUOUS'), # susceptibility
+            ctypes.c_int32,
+            ctypes.c_int32,
+        ]
+        use_nb = False
+        print( "maternal immunity component initialized. Will use compiled C." )
+    except Exception as ex:
+        print( "Failed to load libmi.so. Will use numba." )
+
+
+# Define the function to decrement susceptibility_timer and update susceptibility
+@nb.njit((nb.uint32, nb.uint16[:], nb.uint8[:], nb.uint8, nb.uint8 ), parallel=True)
+def _update_susceptibility_based_on_sus_timer_nb(count, susceptibility_timer, susceptibility, tick, delta):
+    shard_size = count // delta
+
+    # Determine the start and end indices for the current shard
+    shard_index = tick % delta
+    start_index = shard_index * shard_size
+    end_index = start_index + shard_size
+
+    # Handle the case where the last shard might be slightly larger due to rounding
+    if shard_index == delta - 1:
+        end_index = count
+
+    # Loop through the current shard
+    for i in nb.prange(start_index, end_index):
+        if susceptibility_timer[i] > 0:
+            susceptibility_timer[i] = max(0, susceptibility_timer[i] - delta)
+            if susceptibility_timer[i] <= 0:
+                susceptibility[i] = 1
+
+delta = 8
+def step(model, tick):
+
+    global lib, use_nb
+    if use_nb:
+        _update_susceptibility_based_on_sus_timer_nb(model.population.count, model.population.susceptibility_timer, model.population.susceptibility, tick, delta)
+    else:
+        lib.update_susceptibility_timer_strided_shards(
+                model.population.count,
+                model.population.susceptibility_timer,
+                model.population.susceptibility,
+                delta,
+                tick
+            )
+    return