At least 12 geographical vaccination pilots in secondary school aged children in years 7 and 8 have also been added to the flu vaccine programme.
Although winter 2013/14 had low levels of flu, Public Health England has urged healthcare professionals not to become "complacent".
The letter reads: "The annual immunisation programme is a critical element of the system-wide approach for delivering robust and resilient health and care services throughout the year, helping to reduce unplanned hospital admissions and pressure on A&E.
"The continuing extension of the programme to include vaccination of more children this year will not only provide protection to those children but also an increasing opportunity to interrupt transmission of flu to the wider population, thereby saving more lives.
"We are grateful for the efforts from all parts of the system towards the continued implementation of this important enhancement of the national programme."