Missed detections of influenza A(H1)pdm09 by real-time RT–PCR assay due to haemagglutinin sequence mutation, December 2017 to March 2018, northern Viet Nam

There are two methods of reverse transcription polymerase chain reaction (RT–PCR) that have been the common methods to detect influenza infections: conventional and real-time RT–PCR. From December 2017 to March 2018, several missed diagnoses of influenza A(H1)pdm09 using real-time RT–PCR were reported in northern Viet Nam. This study investigated how these missed detections occurred to determine their effect on the surveillance of influenza