Who Should Get Vaccinated First for COVID-19?

Published on December 1, 2020
Photo Credit: Maksim Goncharenok

Vaccines, considered one of the most important advances in modern medicine, have greatly improved our quality of life by reducing or eliminating many infectious diseases. Worldwide, immunization can prevent up to 3 million deaths per year. Vaccines are “one of the most successful and cost-effective public health interventions,” according to the World Health Organization.

As we navigate the next phase in the COVID-19 pandemic, with multiple promising vaccine options in sight, there is much debate on who should be first in line to get vaccinated.

Safe, effective immunization is a critical component in reducing COVID-19-related illnesses, hospitalizations, and deaths. According to the Centers for Disease Control and Prevention’s COVID-19 Vaccination Program Interim Playbook for Jurisdiction Operations, the ultimate goal is to have enough supply available for all who wish to be vaccinated. The supply of vaccine doses will initially be limited, and initial distribution efforts will likely focus on first responders (whether providing direct care or critical support), as well as on those at highest risk for contracting and developing a severe illness from COVID-19.

The CDC’s recently released interim playbook for public health programs and partners provides guidance on how to plan and operationalize a vaccination response to COVID-19. The playbook outlines three phases to COVID-19 vaccination distribution:

  1. Potentially limited COVID-19 vaccine doses available
  2. Large number of doses available
  3. Sufficient supply of vaccine doses for entire population (surplus of doses)

The COVID-19 Vaccination Program Will Require a Phased Approach

Source: CDC COVID-19 Vaccination Program Interim Playbook for Jurisdiction Operations

The goal of Phase 1 is to concentrate distribution efforts on reaching the initial populations of focus. These “critical populations” are defined as meeting one or more of the following criteria (the CDC emphasizes that estimates of these groups should be as accurate as possible):

  • Critical infrastructure workforce: Healthcare personnel and other essential workers
  • People at increased risk for severe COVID-19 illness: Long-term care facility residents, people with underlying medical conditions, people 65 years of age and older
  • People at increased risk of acquiring or transmitting COVID-19: Racial and ethnic minority groups, tribal communities, homeless populations, and similar
  • People with limited access to routine vaccination services: Rural community dwellers, people with disabilities, under- or uninsured groups, and similar

The U.S. government and healthcare agencies need a clear mechanism to accurately define, identify, and estimate critical populations at a national, regional, and local level. Using Carrot Health data and models, our team has developed such a framework.

Since the declaration of the pandemic in March, Carrot Health has invested significant research, data analysis, and predictive modeling resources towards developing a strong understanding of COVID-19 impacts – including identifying vulnerable populations, the social and economic well-being of different communities, and potential long-term effects. We developed two models that are relevant to assessing COVID-19 risk:

  • Carrot Health Social Risk Grouper® (SRG): The Social Risk Grouper (SRG), a proprietary social determinants of health (SDoH) taxonomy, helps the healthcare industry understand, identify, measure and quantify the social barriers and circumstances in which people live. It helps predict the likelihood of an individual having an adverse health outcome due to SDoH and scores every individual in the U.S. with a range of 0 to 99, with 99 being the highest risk.
  • COVID-19 Critical Infection Risk Index: Using factors demonstrated to influence the severity of COVID-19 infection (e.g., smoking status, age, underlying medical conditions), we developed a COVID-19 Critical Infection Risk Index. Risk factor statuses were predicted at an individual consumer level to match the proportion of individuals estimated to have each risk factor by age and gender. This helped us create a simulated dataset to estimate weights for the Index, which then scored at the individual consumer level. The top 10 percent of the calculated index nationwide were labeled as those most likely to be at risk of a “critical case,” defined as an infected patient requiring an intensive care unit level of care/ventilator.

Using these two models, we scored every individual consumer in the U.S. to assess the likelihood they meet the definition of a critical population. These individual-level scores can be aggregated at a census tract, ZIP Code, or county level to help direct vaccine distribution prioritization in Phase 1.

Every county in the U.S. can be stratified into a critical population risk tier. For example, we identified 328 counties, totaling 18 million people, who fall into Tier 1, the highest risk. This tier includes those who scored the highest on the SRG (i.e., more likely to experience an adverse health outcomes) as well as on the COVID-19 Critical Infection Risk Index. Additionally, the second largest population falls into Tier 2, totaling 96 million people, who are also deemed as higher risk index-higher score — just behind Tier 1.

Critical Population Risk Tier by County

Source: Carrot Health

We also scored and mapped every adult across the nation at the county level. The highest risk counties are color-coded in red. While expected, you’ll notice that no state is without at least one county in at least the Tier 1 or 2 category. And some states are hit relatively worse than others.

COVID-19 Vaccination Distribution Critical Population Index in U.S. by County

Source: Carrot Health

Among the challenge identified in the initial phase of the vaccine distribution, we also need to consider the ethics of distribution. Should we prioritize populations at the highest risk of developing a severe COVID-related illness, or at the highest risk of spreading the virus?

Equipping public health agencies and their partners with the appropriate insights and granularity of data can help guide us through this medical ethics dilemma. There is no one-size-fits all approach that works for every community. Rather, we should let the data guide us and inform the emphasis we place on severity vs. transmission.

Through use of Carrot Health data analytics and insights, we propose an appropriate balance of the following dimensions for each targeted community:

  • Target populations at highest risk of spreading the virus
  • Target populations at highest risk for COVID-related mortality and morbidity
  • Educate populations identified as less likely to comply with vaccination

There is light at the end of the COVID-19 tunnel – multiple promising vaccines will soon be available. And while the vaccine supply may be initially limited, decisions about who gets those first doses could save tens of thousands of lives. Informing these prioritization decisions with the right data will help speed the end of the pandemic.

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