A new modeling study published in the Canadian Medical Association Journal shows that unvaccinated people threaten vaccine safety even when vaccination rates against SARS-CoV-2 are high.
The researchers used a simple segmentation model of respiratory viral disease to explore the effect of mixing between unvaccinated and vaccinated people. Subjects were represented as residents of 3 potential sections including susceptible, infected, infectious, and immune-recovering. These compartments were divided to reflect two related subgroups: vaccinated and unvaccinated people.
The researchers simulated mixing between similar groups where people have exclusive contact with others of the same vaccination status as well as random mixing between different groups. When mixing the unvaccinated with the unvaccinated, the risk to the vaccinated people was lower. When vaccinated and unvaccinated people mix, a large number of new infections will occur in vaccinated people, even in scenarios where vaccination rates are high. The cumulative incidence rates among the vaccinated subjects were higher (15%) by random mixing. Unvaccinated participants showed a disproportionate contribution to infection risk after adjusting for contact number.
The results remained stable even when they modeled lower levels of vaccine efficacy for preventing infection, such as those who did not receive a booster dose or with novel variants of SARS-CoV-2. The lower estimate of vaccine efficacy (40%) reflects the uncertainty about the emerging Omicron variant at the time. In contrast, an estimate of the upper limit of vaccine efficacy (80%) reflected the higher efficacy observed with the delta variant.
The authors acknowledge that there are some limitations to the simplicity of their model. Vaccine efficacy against infection but not the additional benefits of vaccination is designed to prevent severe disease and the effect of vaccines to prevent forward transmission by vaccinated but infected individuals. However, the simplicity of the modeling unequivocally illustrates the risk of infection from the unvaccinated.
Opponents of immunizations and immunizations often argue that it is a matter of personal choice or individual rights. However, this study reinforces the fact that an individual or personal responsibility approach to Covid-19 will lead to poor control of the epidemic. The actions of non-vaccinators affect the general population.
A report by Frontiers in Public Health found that the more “singular” a country is, the higher the number of Covid cases and deaths. The report also found that the higher the number of individual participants, the greater the chances that they would not adhere to epidemic prevention measures.
According to the Centers for Disease Control and Prevention (CDC), only 66.1% of the US population received two doses of the Covid-19 vaccine and received fewer boosters. We need more accurate messaging about why vaccination against Covid-19 is important. The original message that Covid-19 vaccines would prevent all infections was unrealistic and inconsistent with the results of other vaccines. But vaccines do not need to prevent infection to be very effective. The inactivated polio vaccine against Salk virus, for example, does not prevent infection or transmission but has been responsible for eliminating polio in the United States and in many other countries around the world.
Vaccination radically reduces the chance of serious illness, death and hospitalization. This reduces the burden on our healthcare systems. If hospitals are overwhelmed with Covid cases, it affects the level of care for all health issues. No person or people is safe from the ravages of Covid-19 until we all survive.
Public health policy and regulations have been developed in the past around behaviors that create health risks to society, as well as individuals. For example, if we have public health laws that limit indoor smoking and driving under the influence of alcohol and drugs, it may be time to consider vaccination against Covid-19 in the same regard.
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