New modelling shows COVID-19 ‘mixed vaccination’ strategy could save more lives

By Melissa Coade

Wednesday June 16, 2021

All thanks to Lady Mary Wortley Montagu’s pioneering inoculation experiments. (Adobe/MandriaPix)

Researchers from Norway and the US have found that population-wide COVID-19 vaccination is most effective when the strategy targets people in the most vulnerable groups first, and then people who are most sociable — alternating between the groups every six months.

According to scientists this kind of dual vaccine strategy could be the best way to reduce deaths from the virus.

“The development of vaccines has opened a way to lower the public health and societal burden of COVID-19 pandemic,” the researchers said.

“To achieve sustainable gains in the long-term, switching the vaccination from one target group to a more diverse portfolio should be planned appropriately.”

Modelling by the researchers showed that a ‘mixed vaccination’ strategy — where half of the available COVID-19 doses were given to the people classified to be in the high risk category of suffering serious effects of the virus, and the other half of doses given to ‘core-sociable’ people — was preferable. They recommend switching vaccination priority between the vulnerable and sociable groups every six months.

“Featuring analyses of all relevant data including age pyramids for 15 representative countries with diverse social mixing patterns shows that mixed strategies (that results in both direct and indirect protection of high-risk groups) may be better for the overall societal health impact of COVID-19 vaccine rollout,” the researchers said.

“Over time switching the priority from high-risk older age groups to core-sociable groups responsible for heightened circulation and thus indirect risk may be increasingly advantageous.”

“One motivation for a cyclic regime is to keep high-risk and high-contact [people in the community] from visiting vaccine-providing centres at the same time.”

The study found there would be a ‘considerably greater reduction’ in the number of people who died from COVID-19 by adopting this strategy over one which vaccinated people in older age groups and only focused on individuals’ direct risk. 

While the current vaccine policy in Australia and most other countries has been to initially vaccinate groups of people according to their relative risk, the researchers suggest that the effectiveness of this approach tends to reduce the ‘burden of mortality’ in the early stages of a rollout. However they also warn that the experience of other infectious diseases shows that the efficacy of ‘critical direct positive measures’ like this can lessen in the intermediate and long term. 

As a result, the scientists argue that vaccine strategies adopted by public health teams should remain flexible.

The study by researchers from the University of Oslo and Pennsylvania State University was published in the Royal Society Open Science journal on Wednesday.


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