Even when SARS-Cov-2 vaccination rates are high, unvaccinated people pose a risk to the vaccinated, says a new modelling study published in CMAJ.
According to an international modeling study, those who have been vaccinated are significantly more at risk of COVID-19 infection when they mix with people who have not been vaccinated.
“Many opponents of vaccine mandates have framed vaccine adoption as a matter of individual choice,” says Dr. David Fisman, Dalla Lana School of Public Health, University of Toronto, with coauthors.
However, they “found that the choices made by people who forgo vaccination contribute disproportionately to risk among those who do get vaccinated.”
To better understand the dynamics of an infectious disease like SARS-CoV-2, researchers built a simple model to investigate the effect of mixing unprotected and vaccinated patients.
They replicated like-with-like population mixing, in which people only interact with those who have the same vaccination status, as well as random population mixing.
When unvaccinated individuals were mixed with unvaccinated, the risk to vaccinated individuals was reduced.
Even in settings where vaccination rates were high, a significant proportion of new infections would arise in vaccinated persons when they mixed with unvaccinated people.
Even when they modelled lower levels of vaccination effectiveness for infection prevention, such as in patients who have not received a booster dose or with new SARS-CoV-2 variants, the authors’ findings remained steady. These findings could have implications for future SARS-CoV-2 waves or the behavior of novel variations.
“Risk among unvaccinated people cannot be considered self-regarding,” they add.
In other words, not getting vaccinated has consequences not only for the unvaccinated but also for the people around them.
“Considerations around equity and justice for people who do choose to be vaccinated, as well as those who choose not to be, need to be considered in the formulation of vaccination policy,” the authors conclude.
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