David Seymour says the new south Auckland community cases show the Government has left New Zealand a "sitting duck hoping for luck".
On Sunday the Ministry of Health (MoH) revealed three new cases - a mother, father, and daughter from the same household in Papatoetoe.
The ACT leader says it proves the Government should have been hardening the country's defences with better contact tracing, testing, and vaccination over the past year.
"It hasn't and we are now reduced to hoping this outbreak will somehow be contained like the January case," Seymour says in a statement.
"The Government has left New Zealand as a sitting duck, hoping for more luck that our isolation has already afforded us. We can only hope for all those who depend on doing business without further lockdowns that our luck hasn't run out yet."
Seymour points to the poor testing of border workers - something covered by Newshub last year.
"The person in question had not been tested since January 18, and her infection has not been discovered until now, four weeks later," Seymour states.
"The Government was warned about failing to test at the border last year but, having papered over that, it appears little improvement has been made.
"We are fortunate that the worker in question got themselves tested outside of the MIQ testing program. Once again, the initiative of Kiwis has saved the day."
Seymour also points to a "mediocre effort" at digital contact tracing.
"The NZ COVID Tracer app remains at less than one million scans per person each day. Practically ineffective. Fewer than one million people have turned on the Bluetooth tracing capability, rendering it ineffective, too," he argues.
Earlier on Sunday Newshub revealed expert concern with our poor QR code scanning rates. Software developer Radhika Reddy said they're a "cause for concern", and wants them to be covered in a rapid audit similar to the one commissioned by infectious diseases expert Dr Ayesha Verrall last May, before the COVID Tracer app was launched.
The ACT Party leader is also critical of the delay in getting New Zealand's vaccination programme underway.
"Even with the vaccine arriving, unexpectedly early and in unknown quantity, New Zealand will barely be in the first 100 countries to begin its vaccination program," he says.
"As ACT has said, not having COVID-19 last month was not a good reason to delay vaccination, it is about preventing an outbreak next month."