Ardern broke the news on social media this morning with a post of a card her daughter Neve had made for Mother's Day.
She said Gayford "woke up feeling a bit average and has tested positive ... so we have 7 days of family time ahead of us!"
She said she and daughter Neve are "fine".
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"I'll be working from home so anyone who watches question time, or is attending my Business NZ speech on Wednesday, you'll still see me remotely."
Neve's card read "Yay! It is Mother's Day. I love fishy kisses. I love you like hot lava!"