diff --git a/covsirphy/__version__.py b/covsirphy/__version__.py
index aa74e09d1..80be2c18e 100644
--- a/covsirphy/__version__.py
+++ b/covsirphy/__version__.py
@@ -1,4 +1,4 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-__version__ = "2.22.0-gamma"
+__version__ = "2.22.1"
diff --git a/pyproject.toml b/pyproject.toml
index e67cfaf7a..b814098a0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "covsirphy"
-version = "2.22.0"
+version = "2.22.1"
 description = "COVID-19 data analysis with phase-dependent SIR-derived ODE models"
 authors = ["Hirokazu Takaya <lisphilar@outlook.jp>"]
 license = "Apache-2.0"