"Unfortunately like all sickness we can't anticipate and it's difficult to plan for situations where staff are unavailable at short notice due to illness so our main concern is to make sure customers know as far in advance as possible."
People can check their buses by using the Metlink app, checking the real-time boards at bus stops or calling the contact centre to see what time their bus is due.
However, there is also the underlying issue of a driver shortage which will cause issues even as sickness improves, if Metlink cannot fill the 120 spaces it needs.
Tramways Union president Gary Froggatt says it's a similar story in Auckland – the long hours, early starts and assaults on drivers make it a less-desirable job choice for newcomers.
"Better pay will help attract more people into the industry, better hours, more friendly more flexible hours could help - I've been in the industry for a long time and the hours and shifts have expanded from eight to 14 hours."
Gain says Metlink is doing its best to attract new drivers in.
"We are trying to what we can to make bus driving a more attractive job – we have increased wages, reduced split shifts but it is a concern and we're trying to do what we can to attract more people to bus driving."
She extended her thanks to all the drivers and customers for their patience, saying Metlink is "incredibly grateful".
"It's a difficult time but it's beyond our control."
