Study shows unvaccinated people are at increased risk of infecting vaccinated people

A new modeling study published in the Canadian Medical Association Journal demonstrates that unvaccinated people threaten vaccinee safety even when SARS-CoV-2 vaccination rates are high.

The researchers used a simple compartmental model of viral respiratory disease to explore the effect of admixture between unvaccinated and vaccinated people. People were depicted as residing in 3 possible compartments, including susceptible to infection, infected and infectious, and recovered from infection with immunity. These compartments have been divided to reflect the two connected subpopulations: vaccinated and unvaccinated people.

The researchers simulated the mixing of similar populations in which people have exclusive contact with others with the same vaccination status as well as random mixing between different groups. When unvaccinated mixed with unvaccinated, the risk to vaccinated people was lower. When vaccinated and unvaccinated people mixed, a significant number of new infections would occur among vaccinated people, even in scenarios where vaccination rates were high. Cumulative infection rates among those vaccinated were highest (15%) with random mixing. Unvaccinated participants made a disproportionate contribution to the risk of infection after adjusting for the number of contacts.

The results remained stable even when they modeled lower levels of vaccine efficacy for preventing infection, such as in those who did not receive a booster dose or with new variants of SARS-CoV- 2. The lower bound estimate of vaccine efficacy (40%) reflected uncertainty about the emerging variant of Omicron at the time. In contrast, the upper bound estimate of vaccine efficacy (80%) reflected the higher efficacy seen with the Delta variant.

The authors acknowledge that there are some limitations to the simplicity of their model. Vaccine effectiveness against infection was modeled, but not the additional benefits of vaccination to prevent serious disease and the impact of vaccines on preventing direct transmission from vaccinated but infected people. However, the simplicity of the modeling unequivocally demonstrates the risk of infection of unvaccinated people.

Those who oppose vaccinations and vaccination mandates often argue that it is a matter of personal choice or individual rights. However, this study reinforces that an individualistic or self-responsibility approach to Covid-19 will lead to poor control of the pandemic. The actions of unvaccinated people have an impact on the whole population.

A report by Frontiers in Public Health found that the more “individualistic” a country was, the higher the number of Covid cases and fatalities. The report also found that the more individualistic participants were, the more likely they were not to adhere to epidemic prevention measures.

According to the CDC, only 66.1% of the US population has received two doses of the Covid-19 vaccine and even fewer have received boosters. We need better, more nuanced messages about why vaccination against Covid-19 is so essential. The initial message that Covid-19 vaccines would prevent all cases of infection was unrealistic and inconsistent with results from other vaccines. But vaccines don’t need to prevent infection to be highly effective. Salk’s inactivated virus polio vaccine, for example, does not prevent infection or transmission, but has been responsible for eradicating polio in the United States and many other countries around the world.

Vaccination also radically reduces the risk of serious illness, death and hospitalization. This reduces the load on our health systems. If hospitals are overwhelmed with Covid cases, it affects the standard of care for all health conditions. No person or population is safe from the scourges of Covid-19 until we all are.

In the past, public health policy and regulation have been developed around behaviors that create health risks for the community, as well as individuals. For example, if we have public health laws that restrict smoking indoors and driving under the influence of alcohol and drugs, it might be time to consider vaccination against Covid-19. in the same way.

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