Primary schools will remain shut in Watford, Three Rivers, London and parts of Essex from the start of term in January.
Education Secretary Gavin Williamson said primary schools in certain parts of England will be asked to stay closed to all except vulnerable children and those of key workers.
The other pupils will be encouraged to use remote learning.
This is a “last resort” the education secretary said, and the majority of areas will have schools opened on January 4.
The schools asked to remain closed in Hertfordshire also include Broxbourne and Hertsmere.