Use of herpes zoster antivirals fell markedly after the launch of a national vaccination program for people in their 70s, suggesting uptake of the jab has previously been underestimated, researchers say.

The vaccine, Zostavax, was added to the National Immunisation Program (NIP) in November 2016, for patients aged 70, with catch-up offered to those aged 71-79.

A study of PBS data shows that scripts for antivirals such as acyclovir and valaciclovir, which had been rising by an average 2% per year since 2006, dropped by 13.6% per year among the target age group in each of the two years after NIP listing.

Although the vaccine was the first for older people funded by the Government in 20 years and heavily promoted, there have been concerns over the uptake, as figures from the Australian Immunisation Register (AIR) suggested coverage of 34% of 70 year olds and just 26% of those eligible for the catch-up.