<prompt> An OPV l shows this symbol on it. What does it indicate?The vaccine has reached its expiry dateThe vaccine has not been stored properlyThe vaccine l is emptyUse the vaccine if expiry date not reached  <response>: The pictures below show the interpretation of vaccine l monitor on the OPV vaccine l: - If color of inside square lighter than outside circle - We can use the vaccine - It is heat sensitive label that indicates cumulative heat exposure over time. 