Adelaide, Nov 4 (IANS): Waning natural immunity has caused a spike in Covid-19 cases in South Australia (SA), the state's health chief has warned.

According to data published by SA Health on Friday, there were 1,691 new cases of Covid-19 and four deaths reported across the state in the latest seven-day reporting window, which ended on Tuesday, reports Xinhua news agency.

It marked an increase of 55 per cent from 1,089 cases in the previous seven-day period and the highest weekly figure since the start of June.

Appearing before a parliamentary inquiry into the state's Covid-19 response on Friday, SA Chief Public Health Officer Nicola Spurrier said the spike was clearly the beginning of a "new wave" of infections, but it was not being driven by the BA.2.86 - or Pirola - variant, which was first detected in Australia in September.

"Predominantly, our cases are still XBB as opposed to being this new variant," Spurrier said, adding that "the reason we're having another wave is because of this natural waning of immunity".

She forecast that SA would experience another spike in cases in approximately six months, and said the gap between vaccination doses was key to preventing major outbreaks.

The latest reported figures took the total number of Covid-19 cases in SA since the start of the pandemic to 939,051 and the total number of deaths to 1,624.

Spurrier told the inquiry that she was very comfortable with the state's public health response to the pandemic over the past four years.

"I would not have done anything differently," she said.