An epidemiologist says historical cases of Covid-19 aren't new - and shouldn't worry people

Six non-infectious historical cases have been reported in a Waikato household that showed symptoms in February after a family member visited from Italy.

A recent covid test after one of them developed a sore throat, has showed the former infection.

Otago University professor Michael Baker says some New Zealanders tested positive on arrival overseas, despite getting over the infection well before.

He says it doesn't pose a risk of virus transmission, and it's not important when it comes to controlling the current outbreak.

Baker says this historical case is the longest-standing sign of past infection he's heard of.