Update vep_handler.py

vep_handler.py

@@ -133,7 +133,7 @@ def fetch_vep(chrom: str, pos: int, ref: str, alt: str) -> VEPResult:
     # Ensembl VEP REST requires no "chr" prefix for human GRCh38
     url = (
         f"{_ENSEMBL_REST}/vep/human/region/"
-        f"{chrom_norm}:{pos}-{pos}/{alt}"
+        f"{chrom_norm}:{pos}-{pos}/{ref}/{alt}"
         f"?content-type=application/json"
         f"&canonical=1"
         f"&pick=1"