diff --git a/HowBadIsMyBatch.ipynb b/HowBadIsMyBatch.ipynb
index 4d7fa23b888..82abff26e63 100644
--- a/HowBadIsMyBatch.ipynb
+++ b/HowBadIsMyBatch.ipynb
@@ -1165,6 +1165,14 @@
     "#### Pfizer Batches"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "f6e460ab",
+   "metadata": {},
+   "source": [
+    "see https://www.howbadismybatch.com/clusters.html"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -1189,16 +1197,13 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "# https://www.howbadismybatch.com/clusters.html\n",
-    "\n",
     "import re\n",
     "\n",
     "batchCodeTable = createADRsByVAX_LOTTable(vaers, \"PFIZER\\BIONTECH\")\n",
     "batchCodeTable['VAX_LOT_PREFIX'] = batchCodeTable['VAX_LOT'].str[:2]\n",
     "batchCodeTable = batchCodeTable.sort_values(by = 'VAX_LOT_PREFIX', ascending = True)\n",
-    "twoLetters = re.compile(r'^[a-zA-Z]{2}')\n",
-    "batchCodeTable = filterColumnOfDataFrameWithRegexp(dataFrame = batchCodeTable, column = 'VAX_LOT_PREFIX', regexp = twoLetters)\n",
-    "batchCodeTable[batchCodeTable['VAX_LOT_PREFIX'].apply(lambda vax_lot_prefix: bool(twoLetters.match(vax_lot_prefix)))]\n",
+    "twoLetterPrefix = re.compile(r'^[a-zA-Z]{2}')\n",
+    "batchCodeTable = filterColumnOfDataFrameWithRegexp(dataFrame = batchCodeTable, column = 'VAX_LOT_PREFIX', regexp = twoLetterPrefix)\n",
     "batchCodeTable = batchCodeTable[batchCodeTable['VAX_LOT_PREFIX'].isin(['EN', 'EP', 'ER', 'EW', 'FA', 'FC', 'FD', 'FE', 'FH'])]\n",
     "batchCodeTable = batchCodeTable[batchCodeTable['ADRs'] > 400]\n",
     "batchCodeTable"