Rinse, repeat: have we again failed to buy enough vaccines?

Australia has organised 25 million COVID-19 vaccine booster doses, 15 million of which won’t be available until the first half of 2022. It’s almost enough to cover our population if children are included in the rollout and there’s no wastage. 

But there’s no clear schedule for when these will arrive or who will be prioritised for the first booster jab. Advice has changed, with modelling from the Doherty Institute showing that prioritising younger people for the vaccine rollout better reduces transmission after the most at-risk are protected.

Worryingly, emerging evidence shows protection from both AstraZeneca and Pfizer wanes after six months. Efficacy drops off further the less spaced-out the first and second doses are for AstraZeneca, a major concern since Prime Minister Scott Morrison recommended decreasing the time between doses from 12 weeks to eight in outbreak settings. 

Australia could well be repeating its current lockdowns in six months time if booster shots aren’t made a priority. 

What does the data say? 

New data from the ZOE COVID study, which asks users to log their vaccinations and COVID-19 test results, analysed data from nearly half a million participants between December 2020 and July 2021.

It found protection from infection for the Pfizer vaccine decreased from 88% to 74% after six months, while efficacy for AstraZeneca decreased from 77% to 67% in the same timeframe for the Delta variant. Another UK study found that every 30 days after the second dose of AstraZeneca, protection dropped by 22%. 

Importantly, both studies focus on protection from infection, rather than protection from severe illness and hospitalisation, which is the most important indicator of success. 

But protection from severe disease seems to be waning too: data from Israel showed the Pfizer vaccine’s effectiveness in preventing serious illness fell from 90% to 80%, though this data hasn’t been replicated in other countries.

What about spacing out the doses? 

AstraZeneca is a safe and effective vaccine with two doses administered between four and 12 weeks apart. Twelve weeks is the optimal spacing, though the Australian Technical Advisory Group on Immunisation (ATAGI) has recommended the time between doses be reduced to between four and eight weeks for those in outbreak settings to boost protection. The recommendation came after Morrison’s call to shorten the timeframe. 

But data has shown that waiting 12 weeks between doses increases efficacy to 81%, while shortening the interval to between four and six weeks decreases efficacy to 55%. Similarly, those who spaced out their Pfizer doses to three weeks had 3.5 times more antibodies at their peak than those who received a second dose within two weeks, while waiting eight to 10 weeks could further boost immunity. Advice for the timeframe between Pfizer doses hasn’t changed in Australia and remains at three weeks.

It’s not clear what impact time between doses has on the vaccine’s longevity, though lower rates of protection is a concern when efficacy is waning. 

How good are boosters?

Vaccine boosters have been controversial. Earlier this month, the World Health Organization called for a moratorium on boosters until at least the end of September so as not to divert much-needed doses from other parts of the world. 

Pfizer has said a booster dose given six months after the second dose elicits an antibody response five to 10 times higher than after two doses, though hasn’t yet released the data to support this.  

AstraZeneca hasn’t yet released a booster dose, with the company’s CEO saying more data is needed to know if booster shots are necessary. Administering one dose of AstraZeneca followed by one dose of an mRNA vaccine such as Moderna or Pfizer may produce a stronger immune response than two of the same vaccine. 

When do we need the boosters by? 

Australia’s vaccine doses started ramping up in May, meaning protection against severe disease for those in residential aged care settings who were prioritised in the early phase of the vaccine rollout might start dropping around November. 

NSW has recorded the fastest daily vaccination rate in the world and is estimated to reach 70% of those aged over 16 fully vaccinated by the end of October, with the rest of Australia not far behind.

That means we need all of our boosters ready for arms by April at the latest, and no timeframe has been established for when the boosters will arrive. With no AstraZeneca booster yet released, our onshore manufacturing capability is zilch, and mRNA vaccine manufacturing facilities won’t be ready by next year. 

Australia may enjoy a brief period of freedom once we hit 80% vaccination rates — but as we learn to live with the virus, hospitalisation rates could increase as vaccine efficacy wanes.