COVID-19 vaccination alone might not finish the pandemic

A simulation-based study at Miami University, USA, found that vaccinating the general population against Coronavirus Disease 2019 (COVID-19) alone, given current availability and implementation strategies, is not enough to control the pandemic. In order to override the current infection rate of Coronavirus 2 with Severe Acute Respiratory Syndrome (SARS-CoV-2), the strict implementation of non-pharmacological control measures should be continued along with mass vaccination programs. The study is currently available on the medRxiv * preprint server.


The United States of America is among the countries hardest hit by the ongoing COVID-19 pandemic. According to the World Health Organization, of 104.8 million SARS-CoV-2 infections and 2.28 million COVID-19 deaths worldwide, there are more than 26 million cases and over 450,000 deaths in the United States alone. In addition, there is evidence that the pandemic reduced the life expectancy of U.S. citizens by more than a year, which is ten times more severe than the decrease seen during the opioid epidemic.

In the early stages of the COVID-19 pandemic, non-pharmacological control measures were seen as the best possible way to contain the spread of the virus. These measures mainly include wearing face masks, hand washing, social distancing, restricted movement, contact tracing, and quarantine strategies. However, in the later stages of the pandemic, several potential vaccines were launched in many countries, raising hopes of a return to normal life amid the pandemic situation. In the U.S., the FDA recently approved two COVID-19 vaccines for limited and emergency use.

In the current study, scientists assessed the effectiveness of nationwide COVID-19 vaccination programs, public vaccine adoption, and daily vaccination capacity under two federal plans proposed by the former Trump administration and the Biden administration. In addition, they examined the correlation between non-pharmacological control measures and vaccines in treating the COVID-19 pandemic.

Overview of our modified COVASIM model with the state diagram and the specification of all transitions, including the most important procedures for vaccinations and infections.

Overview of our modified COVASIM model with the state diagram and the specification of all transitions, including the most important procedures for vaccinations and infections.

Study design

In the current study, scientists performed extensive single-level simulations by expanding a validated open source COVID-19 model (COVASIM) based on vaccines with vaccine efficacy, implementation capacity and public acceptance. Using the model, they simulated the need for two doses of vaccine and the likelihood of infection before receiving the second dose. They also investigated whether there is a connection between vaccination interventions and non-pharmacological interventions in managing the pandemic situation.

Important observations

The comparison between two federal plans found that the Biden plan (1 million vaccine doses / day) is more effective in fighting SARS-CoV-2 infection than the plan created by the previous Trump administration ("Operation Warp Speed"). According to the simulation data, the envisaged vaccination schedules can significantly reduce the number of COVID-19 cases even if public vaccine readiness is insufficient and effectiveness is less than expected. Between vaccine effectiveness and vaccine compliance / acceptance, it has been observed that increasing the effectiveness of the vaccine can significantly reduce the rate of infection and induction of the proportion of immune subjects in a given population, which is critical to achieving herd immunity. In contrast, predictions of vaccine acceptance showed more complex results.

In particular, the scientists hypothesized that increased vaccine acceptance is associated with decreased infection rates. However, the simulation data mostly showed reversed results for both vaccination schedules, especially under conditions with the lowest constraints on non-pharmacological control measures. Scientists believe that since vaccination programs are primarily aimed at immunizing older populations with much less social interactions than the younger population, the real impact of vaccination on reducing virus spread is largely offset. Another reason for such reverse results could be the low availability of vaccines. In both situations, the risk of infection transmission for the younger population continues to increase until they are eligible for vaccination. This can lead to a general induction of the rate of infection in a given population.

Study significance

The study results show that vaccination programs alone cannot control the pandemic, although they are effective in reducing the infection rate. In a situation where the non-pharmacological control measure is largely relaxed, it is difficult to achieve herd immunity through vaccination alone. Similarly, in situations where there is no restriction on control measures, higher public compliance with vaccination regulations leads to a higher infection rate, mainly due to the low availability of vaccines and / or the priority of vaccinating the elderly. Even as vaccination programs progress, the implementation of non-pharmacological control measures should therefore continue to strictly lead to a normal state of life in the midst of the pandemic.

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

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