It brings the total number of infections to 57, say UK health officials.
Parents say they are "horrified" that similar warnings have been issued after four deaths.
The warning comes as seven cases of new "variants of concern" are detected in Northern Ireland
Other groups have reported higher protection, but the results are still seen as a triumph.
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Borrowing - which hit a record £22.3bn in October - cannot go on indefinitely, chancellor says.