Reinfections with COVID-19 are becoming more common across the country in the wake of new sub-variants of the virus, according to an infectious diseases expert.

As more people become became eligible this week to receive a fourth vaccine dose, as well as antiviral treatments, Associate Professor Paul Griffin from the University of Queensland said people should not become complacent surrounding the virus.

He warned those who have recently come down with COVID-19 could become reinfected in a matter of weeks.

“We are seeing reinfections being more common and in short intervals, and that is why we recommend the reinfection period be reduced to four weeks,” he told the Seven network on Tuesday.

“If you get symptoms again, you need to assume it could be a new infection.”

It comes as the Australian Health Protection Principal Committee recommended the reinfection period be reduced from its current 12 weeks to 28 days, following the rise of cases of the BA.4 and BA.5 Omicron variant.

Associate Prof Griffin said the rise in new COVID-19 infections alongside an increase in influenza cases was also concerning.

“This is translating into significant numbers in hospitals, with predictions … we may exceed the hospitalisations we saw in the first big wave in January,” he said.

“We cannot assume people are protected just because they’ve had COVID, you need to be up to date with your vaccines and linking with therapies if you are eligible.”

However, doctors have said antiviral treatments, which have become more readily available, are not a substitute for being vaccinated.

Royal Australian College of GPs vice-president Bruce Willett said the two measures were important but should be seen as having separate functions.

“One of the concerns with these antiviral agents is people may see them as a substitute for getting vaccinated – they definitely are not,” he told Sky News.

“Vaccination is still our first and foremost protection against severe COVID.”

He said vaccination could reduce a person’s chances of hospital admission or getting severe disease by a factor of five.

Dr Willett noted there was a problem in some rural and regional areas in getting access to the antiviral drugs, but it was likely to improve.

“We have all been caught a little bit on the hop with the expansion of the availability,” he said.

Australians over 70 who test positive for the virus were from Monday offered access to antivirals on the Pharmaceutical Benefits Scheme.

Access was also 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.

Normally costing more than $1000, the two antiviral treatments are now available for $6.80 for concession card holders and about $40 for everyone else.