Diseases like influenza have virtually disappeared in Australia during the COVID-19 pandemic, but one acute and highly contagious virus has remained stable despite strict restrictions and social distancing.
More than 10,000 cases of varicella-zoster virus, which causes chickenpox, were recorded in Queensland last year and similar levels were seen in 2020.
It has a reproduction number (R value) as high as 13, meaning that one infected person can pass on the virus to as many as 13 others, depending on immunity levels.
Queensland Health said the virus could spread easily among people who have not had the disease or had not been vaccinated against it.
Other diseases also dropped, with the number of flu cases dropping from 6,047 in 2020 to 296 last year.
No lock for the pox
University of Sydney infectious diseases expert Robert Booy said the figures showed how transmissible chickenpox was.
"Its effective reproductive number can be anywhere between about three and 13," he said.
"So the efforts we make to socially and physically distance become ineffective in the face of a virus that is so highly transmissible."
Chickenpox is transmitted through close contact, either by air or direct contact with fluid from the blisters it causes.
Queensland Health said it believed chickenpox case numbers had remained high due to a combination of reasons, including that young children were still in the process of learning basic hygiene practices.
Check your vax status
Clare Walker, a GP and secretary of the Rural Doctors Association of Queensland, said it was important for people – especially pregnant women – to check their vaccination status for chickenpox.
"It's been around for a long time and will be with us, probably, for a long time yet — not one that we're probably going to get rid of," she said.
"For older children or teenagers and young adults, there are some of them who will not have had chickenpox and didn't get the vaccine when they were small.
Dr Walker warned the disease could have severe consequences for those without immunity.
"In adults, they can get encephalitis – so an infection in their brain – and you can get quite a nasty pneumonia, which can be fatal," she said.
When a person recovers from chickenpox, the virus stays dormant in the nerves close to the spine and as a person gets older, it can rear its head in the form of debilitating, painful shingles.
Under the National Immunisation Program, children from the age of 18 months can access a free measles, mumps, rubella, varicella vaccine, which provides 80 to 85 per cent protection against chickenpox.
Queensland Health said it was particularly effective against severe illness, offering 95 to 98 per cent protection.
Nothing to party about
Dr Booy said he hoped so-called "chickenpox parties", where parents tried to deliberately infect their children, were a thing of the past.
"It's a rare event that people want to pass chickenpox from one child to another," he said.
Dr Booy said the pandemic had shown social and physical distancing had been very effective in limiting the spread of diseases.
But he warned the public to expect the number of infectious diseases to increase once those measures ended.
"As borders open up and as we stop wearing masks and proceed to interact more physically, with hugs and kisses with our friends and neighbours, those diseases will again become more common," he said.
