The United States is only days away from achieving President Biden’s goal of vaccinating 100 million people 100 days from taking office. While the United States leads the world in the number of COVID-19 cases at more than 29.7 million and deaths topping 539,000, the United States has stepped in as a leader in the vaccination of its population.
However, the current vaccination strategy is not considered basic reproduction number (R0), which helps predict the spread of COVID-19 cases.
New preprinted research paper published in medRxiv* servers by Anthony R.Ives of the University of Wisconsin-Madison and Claudio Bozzuto of Wildlife Analysis GmbH suggest current vaccination efforts will reach the United States herd immunity in about 4.5 months. However, they argue that a more cost-effective and more effective vaccine strategy that takes geography into account. This will help allocate vaccines to districts with high populations that tend to be lower class and with high minority populations. These countries are currently on track to be the last to achieve herd immunity under current vaccine distribution strategies.
The author writes:
“From an epidemiological perspective, because of the difference in R0 value between districts is driven partly by population density, districts with the highest risk of bouncing back and the most recent severe outbreaks achieving herd immunity. From a socio-economic perspective, these high density districts include many of those that are economic engines in the US. Finally, high-density districts have relatively large African-American populations, and current distribution plans cause a delay of about 4 days behind whites achieving herd immunity. “
Target vaccination strategies proposed by high R countries0 number
Given that urban environments are at high risk of spreading the virus, the dense population results in a higher estimate of R0. Therefore, the authors argue that vaccination strategies should target densely populated populations to achieve herd immunity faster and avoid more cases of COVID-19.
To calculate it, they tracked the proportion of the US population that would attain herd immunity under the current distribution strategy. Starting from March 15, 2021, they assumed the following: Current vaccination rates using one of the three FDA-approved vaccines – Moderna, Pfizer-BioNTech, or Johnson & Johnson – would be 1.58 million doses per day when 71.1 million people are already vaccinated with at least one dose, the vaccine is 90% effective, and vaccinated people cannot spread COVID-19.
Their results showed herd immunity in the United States could be achieved in as little as 130 days.
Allocation of the appropriate and efficient SARS-Cov-2 vaccine according to R0. Panel (a) shows the proportion of US residents living in districts who have achieved herd immunity, calculated as 1 – 1 / R0 at the district level; day 0 on the x-axis is March 15, 2021. The black line assumes the current distribution in which vaccine is evenly shipped to states according to population size, and the red line assumes the distribution depends on the estimated district-level R0 value. Panel (b) shows the mean population density of districts (individuals per km2) achieving herd immunity in the weekly time window. Panel (c) provides the proportion of white and African American communities living in states that have achieved herd immunity.
The new plan achieves herd immunity faster in all regions
Instead, their analysis suggests that their proposed strategy would help the United States achieve nearly equal herd immunity for all counties and 51 days earlier than the current vaccination strategy. Additionally, the United States will eventually use 39% less vaccine under the new plan.
“This result depends on R0strategy based starting mid-March; the overall benefits are expected to shrink the longer population size-based strategies are maintained. “
With new variants of concern from the UK, South Africa and Brazil, researchers note these estimates may change, and more vaccinations may be needed.
To account for the new variant’s higher transmission rate, they adjusted the mathematical formula to include 1.5 times higher transmission than initially measured at the start of the pandemic in 2020.
The findings suggest that with the strategies proposed by the researchers, the United States would reduce the time to achieve herd immunity to 76 days and use less than 35% of their vaccine dose.
Evidence suggests that scaling up vaccination efforts in more populated countries will be fairer and more efficient, use less vaccine in the long term, and achieve herd immunity faster.
* Important Notice
medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be construed as conclusions, guidelines for health-related clinical / behavioral practice, or are treated as defined information.