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If it is already there than she will, most likely, have already have been exposed - however, I would take any excuse to get as long a holiday as possible as I love the summer holidays! Especially if you think she is going to spend some of it feeling ill!
FWIW, my dd had a confirmed case in her class last week. School have carried on as normal (apart from sending home those who were unwell) and she's been absolutely fine. Don't think it's necessary to keep them off unless they have other health problems tbh.
Dc's have just come back with a letter stating 2 confirmed cases in their school (small primary). I feel anxious for all of us but mostly my 10 day old baby. Thinking same as you Minko. Ds is leaving to go to secondary and would miss all leaving dos. My hv recommended that I avoid large gatherings with the baby this am and that was before this letter this afternoon. I'm not sure what to do.