The Australian Health Protection Principal Committee, the federal government’s peak decision-making body for disease control, recommended on Friday that the immunity time for COVID-19 cases be cut to 28 days amid the rise of the new BA.4 and BA.5 Omicron subvariants.

Previously, people who had recovered from the virus were exempt from being a close contact or a positive case for 12 weeks.

“BA.4 and BA.5 are associated with increased immune escape and we are likely to see rates of reinfection rise among those who have previously been infected with an earlier COVID-19 variant and those who are up to date with their vaccinations,” AHPPC said in a statement on Friday.

“Given reinfections may occur as early as 28 days after recovery from a previous COVID-19 infection, the AHPPC advises that the reinfection period be reduced from 12 weeks to 28 days.”

The latest genome sampling from SA Health shows 11.7 per cent of infections are BA.4 and 12.6 per cent are BA.5.

The majority of cases, 68.6 per cent, have been BA.2.

Health Minister Chris Picton said the AHPPC recommendation was “unfortunate” but reflected the reality of the new Omicron subvariants.

“For 12 weeks people have had this get out of jail free card for COVID, unfortunately what we’re seeing with BA.4 and BA.5 has a lot more immune escape compared to previous strains,” he told ABC Radio Adelaide today.

“So if you’ve had BA.1 and BA.2 in previous waves that we’ve seen, that isn’t necessarily going to protect you from BA.4 and BA.5.”

Chief public health officer Nicola Spurrier said reinfections were on the rise in South Australia.

“One of the things that we’ve noticed here in South Australia is that people have been getting new infections within the three months,” she told reporters on Sunday.

“We are learning more about BA.4, BA.5, the severity doesn’t seem to be any worse but you could have symptoms that are on par or even more severe than with that initial infection.

“The infection itself doesn’t seem to be giving you very much protection.”

She said the state’s health situation was “very much more complex now” with the number of different variants and varying levels of immunity.

SA Health reported two COVID-19 deaths and 3039 cases on Sunday, down from the 3246 reported on Saturday, although testing numbers also decreased 33.9 per cent from the day before.

There are 240 people in hospital and nine in intensive care, including two on a ventilator. Wednesday’s deaths included a woman in her 50s and a woman in her 90s.

SA Health-commissioned modelling forecasts the state is still on track to record between 5000 to 6000 daily COVID cases within two weeks’ time.

It comes as South Australians aged 30 to 64 can from today come forward for a fourth dose – or second booster – of a COVID-19 vaccine.

The change in eligibility will see an extra 491,000 people eligible for a fourth shot in South Australia and 7.4 million across the country.

People over 50 are recommended to get the extra shot while those over 30 are eligible if they wish.

“The strong recommendation is for people over the age of 50 to take that up,” Picton told ABC Radio today.

“This will be available not only through 600 different GPs and pharmacies across the state, but also through SA Health clinics as well.

“This is going to mean a lot of people get that boost to their immunity before we see more cases increasing.”

Meanwhile, federal Health Minister Mark Butler announced on Sunday that Australians over 70 who test positive to the virus will be able to access antivirals on the Pharmaceutical Benefits Scheme from Monday.

Access will also be expanded to people over 50 with two or more risk factors for severe disease and Aboriginal or Torres Strait Islander people over 30 with two or more risk factors.

Anyone 18 or over and immunocompromised may also be eligible.

Two antivirals are on the Pharmaceutical Benefits Scheme: Lagevrio and Paxlovid. Normally costing more than $1000, they will be available from Monday for $6.80 for concession card holders and about $40 for everyone else.

A new advertising campaign will also be launched to educate Australians about the availability of treatments.

The Plan For COVID campaign encourages people to test at the first sign of symptoms, talk to their doctor without delay for advice and seek treatment options.

Butler said hospitals are bracing for increasing cases as winter progresses and encouraged younger Australians in particular to get their third shot.

About 2.5 million people in their 30s and 40s are yet to have their third dose, he said.

“I really encourage you to get out and get that (third) dose because that’s the big kicker. That’s the thing that really lifts your immunity against severe disease,” Butler told reporters in Adelaide on Sunday.

“The fourth dose will give you a boost and that boost is important right now because of the phase of the pandemic we’re going through, this additional third wave.”

More than 31,000 new infections and 24 deaths were reported across Australia on Sunday, a slight dip on the previous 48 hours.

There were 4094 Australians in hospital by the end of the weekend, with increasing influenza rates adding to the pressure on healthcare staff.

– With AAP