New research makes the case for third COVID booster

By Melissa Coade

November 19, 2021

All people 16+ who have received a booster dose are considered ‘up-to-date’.  (Prostock-studio/Adobe)

A new study by Australian scientists has been published underscoring the need for booster shots against COVID-19 strains, including a third booster within one year after a full primary vaccination schedule.

Dr Deborah Cromer, a lead author of the study, said the new findings showed that after the first few months of receiving a COVID vaccine, the vaccine would offer reduced efficacy against the disease resulting from other variants like the Delta strain. In order to maintain immune protection across a population, she advised that booster shots were required.

“Vaccines work well in the first months after vaccination and against the viruses that were used to make them,” Cromer said.

“This efficacy declines with time, and our analysis is able to pre-emptively predict this decline based on analysis of antibody levels.”

The Australian analysis predicting protection against variants using neutralising antibodies to inform vaccine rollouts has been described as the ‘first and largest study’ of its kind. The researchers say that it gives policymakers a clearer picture about how levels of protection against severe health outcomes are likely to change based on different vaccines and emerging virus variants over time.

By identifying an ‘immune correlate’ of vaccine protection, the researchers from UNSW Sydney’s Kirby Institute, the Sydney Institute for Infectious Diseases at the University of Sydney and the University of Melbourne’s Doherty Institute believe their analysis can help inform the government’s COVID-19 response. 

Dr Cromer explained that previous research showed that it was possible to measure neutralising antibody levels as a ‘proxy’ for immune protection from COVID-19 infection. 

“In this new analysis, we’ve tested this against the variants of concern, including Delta, and found that the model continues to provide a robust prediction of immune protection, despite the differences between the viral sequence seen in variants like Delta,” Cromer said.

“Without boosters, protection from symptomatic COVID may drop below 50% after six months, which means more people will become infected. Reassuringly though, protection against severe disease and death will likely remain high over the first year.”

The Kirby Institute researcher added that the TGA’s recent approval of booster doses of the COVID-19 vaccine after six months from being fully vaccinated would ‘help maintain high levels of protection against all stages of disease’. The paper also recommended that a third booster shot be made available to people within a year of receiving their second vaccine dose, which would increase immunity to levels higher than seen after a full primary vaccination schedule.

“Optimal timing for boosters will depend on the availability of boosters, and whether the aim is to reduce overall case numbers or reduce the burden on the heath system,” Cromer said.

“Vaccines have had an incredible impact on controlling the current COVID-19 outbreak and will continue to provide very good protection. But boosters will make that good protection even better,” she said.

The University of Sydney’s Professor James Triccas said the new analysis showed that vaccine efficacy could be effectively predicted from a relatively simple laboratory test — this being very useful information to plan for the impact of future COVID strains.

“It is likely that new COVID-19 variants will continue to emerge, as we have seen with Delta, with varying transmissibility and severity,” Triccas said.

“Vaccines may not work as well against some of these variants, but fortunately, our model allows us to predict this.”

“Essentially, we can predict how current vaccines will work against new variants, and test the efficacy of new vaccines, based on the results of small clinical trials that measure antibody responses. That’s a huge win for the battle against COVID-19,” he added.


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