Giving a COVID Vaccine to This Age Group First Would Be the Most Effective Way of Stopping Spread, Study Finds

Giving a COVID-19 vaccine—if and when one becomes available—to people in the 30-59 age group first would be the most effective way of curbing the spread of the SARS-CoV-2 virus, a study has found.

In a pre-print paper—meaning one that has not been peer-reviewed—posted to the online server medrxiv.org, an international team of scientists concluded that initially targeting any coronavirus vaccine to young and middle-aged adults in this age group could "more than double" its effectiveness when it comes to reducing transmission of the virus.

The team found that in 179 countries, individuals between 30 and 59 years of age tend to be the "highest priority" group because of high contact rates with others, as well as higher risk of infection and disease.

The researchers said that targeting the allocation of a vaccine could have a significant impact on its effectiveness.

"The vaccine should be initially targeted to young and middle-aged adults as these individuals are the most likely to become infected and transmit infection," Michael Meehan, lead author of the study from James Cook University in Australia, told Newsweek. "By targeting specific age groups we can substantially reduce the number of doses required to achieve an equivalent reduction in transmission—compared with un-targeted strategies."

"Since it is unlikely that the vaccine will be 100 percent effective in all recipients, very large fractions (80-90 percent) of the population will be required to be vaccinated in order to achieve herd immunity, through vaccination alone. However, this fraction can be considerably reduced—for example, by 50-60 percent—if doses are targeted to priority age groups."

Meehan said the extent to which individuals contribute to the spread of COVID-19 can be down to many factors. But the most important of these are: their probability of becoming infected following contact with an infectious individual; their probability of developing symptomatic and severe disease following infection; and the number of contacts they make with other members of the population.

The team's analysis of different age groups based on mathematical modelling shows that, in most cases, young and middle-aged individuals were the greatest contributors to the transmission of the virus, and, thus, should be targeted first with any vaccine.

"We decided to investigate COVID-19 vaccination strategies in attempt to look ahead at the next steps in SARS-CoV-2 infection control," Meehan said. "Anticipating that the initial deployments of vaccine will be limited—assuming a safe and effective vaccine is eventually approved—we thought it was critically important to attempt to optimize the delivery of those doses that are made available to ensure the maximal disruption to transmission."

According to the World Health Organisation, there are more than 100 COVID-19 vaccine candidates in development, with a handful of these in the human trial phase.

The study suggests that the number of vaccine doses required to reduce transmission of the virus—and potentially achieve elimination—may be considerably lower than initial estimates.

But since asymptomatic carriers of the virus contribute significantly to its spread, the impact of any potential vaccine is "critically dependent" on the type of protection it provides, the authors said.

"Vaccines that help prevent individuals from becoming infected have a far greater impact compared with those that allow individuals to become infected but prevent them from developing symptomatic disease," Meehan said.

Thus, some countries may not be able to achieve herd immunity through vaccination alone—whether or not doses are targeted—since it is unlikely that the vaccine will be 100 percent effective in all recipients.

The authors note that they decided to come up with the most effective strategy for reducing transmission. But other studies have decided to focus more on reducing deaths or ICU hospitalizations, for example. In these cases, researchers found that older, more vulnerable individuals, should be the first groups to be targeted for vaccination.

Perry Halkitis, dean of the Rutgers School of Public Health, who was not involved in the study, told Newsweek that deploying vaccination in a targeted manner made sense from the perspective of mathematical modeling, but is "insufficient" from a public health perspective, as other factors must also be taken into account.

"The group of individuals ages 30-59 is not monolithic and differences exist within this age groups both within and across the countries included in this analysis," he said. "The [study] assumes that there is homogeneity in that age group that clearly does not exist in terms of risk-taking behaviors or environmental factors that precipitate risk."

"It is incredibly important to deploy the vaccine to those most at risk within this 30-59 age group, specifically frontline workers including grocery store employees, food servers, mail carriers, healthcare providers among many others. Many of our essential workers are also members of racial and ethnic minority groups, which experience greater health disparities due to social conditions that are perpetuated by racism and discrimination, putting them at an especially heightened risk."

In addition, he said people with underlying chronic health conditions and the elderly are especially vulnerable.