How the Delta Variant Impacts Vaccination Strategies

The piece you’re about to read is from Klick Health’s Life (Sciences) After COVID-19 series, a collection of expert perspectives designed to inform and inspire the life sciences community for the coming changes and opportunities we anticipate as a result of this global health crisis.

Throughout the COVID-19 pandemic, the Klick Consulting and Applied Sciences teams have been closely researching infection data from several sources to better understand the nature of the pandemic and how it has been evolving.

During the global vaccine rollout, our team took a keen interest in tracking the data and manually scraped daily case and death counts from December 1, 2020 through July 30, 2021 from 192 countries to understand the impact of vaccines as they became more widely available.

Analysis A: Change in cases and deaths over time

First, we wanted to understand how cases and deaths were impacted by the delta variant’s emergence in the population. Figures 1 and 2 visualize cases and deaths over time split by First-Dose-First and Full-Dose countries.

In essence, the First-Dose-First strategy is a public health strategy looking to maximize the number of individuals with partial COVID-19 immunity by giving one vaccine dose to as many people as possible, as quickly as possible. The Full-Dose strategy seeks to maximize the number of fully protected individuals by giving full vaccine doses to as many people as possible, as quickly as possible.

The methodology for determining whether a country is classified as a First-Dose-First or a Full-Dose country for the purpose of these analyses is set out in the Methodology and Terminology section below.

What is of note in Figure 1 is the similarity in the change in cases prior to the emergence of the delta variant and the drastic difference afterwards. The First-Dose-First strategy made sense prior to the new variant but it is no longer as effective. In Figure 2 we see that in contrast to the case rates, the death rates were always more successfully curbed in countries following the Full-Dose strategy. This was exacerbated after the expansion of the spread of the delta variant in early April.

Another important note from this analysis was that the uptick in cases seen since the beginning of July due to the increase in the delta variant had not yet resulted in an increase in deaths.

One possible explanation for this is that deaths are typically a lagging indicator (meaning it takes some time after infections increase before deaths also increase) so it may not yet be visible in the data. The other is that the Full-Dose vaccination strategy is preventing a rise in the number of population-wide deaths by immunizing (or drastically reducing the severity of infection in the event of breakthrough infections) those most likely to suffer hospitalizations or deaths if infected.

Figure 1—Since the rapid increase in delta variant, the Full-Dose strategy has become less effective for decreasing the case rate

Additional analysis must be done to compare the level of vaccination rates between the strategies.

Figure 2—Death rates have been consistently decreasing within Full-Dose strategy countries

Additional analysis must be done to compare the level of vaccination rates between the strategies.