What to do about shifting AZ advice

The fact the advice regarding the AZ vaccine has changed four times since early April may therefore simply reflect the fast-moving nature of the pandemic. Picture: Aaron Francis

Last week, as Australians were confined in yet another round of lockdowns, Scott Morrison urged the Australian Technical Advisory Group on Immunisation to review its advice, which unconditionally recommended the AstraZeneca vaccine only for over-60s. Following that request, ATAGI updated its view and recommended the vaccine’s broader use.

ATAGI’s mandate is ‘‘to provide technical advice to the minister for health on the medical administration of vaccines available in Australia”. It is understandable that ATAGI would periodically reassess its advice as it responds to additional clinical information and to changes in the disease environment, including in the extent of community transmission, the virus’s infectivity and the severity of the disease.

The fact the advice regarding the AZ vaccine has changed four times since early April may therefore simply reflect the fast-moving nature of the pandemic. Nonetheless, it is troubling that ATAGI, in revising its views during outbreaks, has repeatedly said its “recommendations for non-outbreak settings remain unchanged”.

That approach smacks of advising that precautions be taken against bushfires only when fires are raging. Yet, as with bushfires, the pattern with Covid-19 has been one of outbreaks that are then extinguished (in Covid’s case by lockdowns), leading to periods of quiescence. A rational forecaster would take that pattern into account and, even in the lulls, incorporate the likelihood of future outbreaks into its recommendations about mitigating risk.

Instead, ATAGI’s scenarios are based on an underlying pattern of low, medium or high rates of infection that persist at a constant level for the entirety of its assessment period. That leads it to underestimate the individual benefits of vaccination – helping to induce low rates of vaccination – and then forces it to suddenly shift course when outbreaks occur, undermining the value of its advice.

But that difficulty is merely symptomatic of a deeper problem with ATAGI’s methodology. At the heart of ATAGI’s approach is a comparison of two potentially serious risks, which it assesses from the standpoint of the individual deciding whether to be vaccinated: those associated with Covid and those of vaccination.

The risks arising from vaccination are analytically straightforward: if one has the jab, there is a determinate probability of an adverse reaction. But the risks associated with Covid are more complex because they are affected by the policy response which, in turn, is affected by the vaccination rate that ATAGI itself influences.

Thus, it is obvious the risk of community transmission can be reduced through harsh restrictions on activity. But it would be absurd if ATAGI implicitly assumed those restrictions were or would be speedily put in place, thus artificially lowering the estimated risk of catching Covid, discouraging vaccination and hence making continuation of the stop-go pattern virtually inevitable. In the short run, that would be a self-fulfilling prophecy; in the longer term, it would damage ATAGI’s reputation by forcing one reassessment of risk after the other.

Rather, just as we recommend taking precautions against bushfires as if lives and properties are going to be in danger instead of being saved by firefighters, so ATAGI’s work should include a central or reference scenario that realistically takes account of the fact the stop-go cycle cannot persist forever. In that way, it would be modelling an exit from the pattern and allowing Australians to measure the risks they will face if they choose to remain unvaccinated.

We are not suggesting ATAGI should only model that reference scenario; nor are we implying that modelling that scenario would be easy. ATAGI has a difficult job to do, which it has undertaken competently and professionally. But as the Delta variant moves the pandemic into a new phase worldwide, the old Roman saying may be unusually apt: Per aspera ad astra – we go through difficulty to the stars.