First fully peer-reviewed modelling shows need for comprehensive COVID-19 vaccination coverage
Epidemiological modeller A/Prof James Trauer has worked with Queensland colleagues on new modelling that shows Australia’s current COVID-19 vaccination program, featuring aged-based stratification of AstraZeneca and Pfizer, will not achieve herd immunity unless 85 per cent of the population, including many 5-16 year olds, are double vaccinated.
The research was led by James Cook University researcher Professor Emma McBryde with extensive collaboration from several staff of the Epidemiological Modelling Unit, including Romain Ragonnet and Pavithra Jayasundara.
It was published today by the Medical Journal of Australia, and provides the first fully peer reviewed estimates for Australia’s pathway to re-opening as vaccination rates increase.
The model explores a range of pre-vaccination effective reproduction numbers for the Delta variant, starting from a value of five. At a lower effective reproduction number of three, the mixed program can achieve herd immunity at 60-70 per cent coverage without vaccinating 5-14 year-olds. If that value is increased to seven, herd immunity can’t be achieved with the current vaccines. The value of five is significantly higher (and hence more conservative) than that used in Australia’s National Plan modelling.
Even at the highest value of seven, the researchers emphasise that vaccination still prevents over 85 per cent of deaths, compared with no vaccination.
The model incorporates age-specific population mixing, viral infectiousness, susceptibility and severity to estimate the final scale of the pandemic under various public health interventions across Australia. The predicted endpoints include the final numbers of infected people, cumulative hospitalisations, deaths and years of life lost.
A/Prof Trauer said, “With the outbreaks in New South Wales and Victoria growing alongside the vaccination program, a shift away from vaccinating the vulnerable and instead concentrating on vaccinating those with the highest likelihood of spreading the virus becomes increasingly important.
“Australia is unlikely to achieve herd protection unless vaccination is extended to younger ages or combined with other measures, and the national strategy should now prioritise delivering Pfizer vaccine to 16-39 year-olds.
“The bottom line for Australians is if you can get vaccinated, do it, and continue to adhere to mask-wearing and other public health interventions until we have reached those higher levels of coverage.”