Dallas County Coronavirus (COVID-19) Updates and Information

The term “herd immunity” describes a situation where a high enough percentage of the population is immune to an infection that the infectious organism can no longer circulate and continue infecting people. The population percentage at which herd immunity is reached increases with the infectiousness of the infecting organism. Early in the Covid-19 pandemic, the degree of infectiousness of the initial virus suggested that herd immunity might be reached when 70%-90% of the population are immune, either from vaccination or infection. However, as viruses spread throughout a population, they can change over time to produce variants. As the 50% more infectious Alpha variant has taken over, herd immunity requires a higher percentage of immunity, and as the even more highly infectious Delta variant completely takes over, the percentage will be even higher. Above all, we will know when we have reached the point of herd immunity when new Covid-19 cases are no longer appearing.

PCCI has been taking into account every variant, all data to date, or the duration the immunity lasts. The impact of the Delta variant has NOT yet been factored into the PCCI herd immunity models and new and reliable scientific studies in major scientific journals (Nature, NEJM, and others) have just started to come out with new important evidence that will affect these estimates. It is becoming evident that the Delta variant is changing the game significantly. It’s doing it in two ways:

1. By being much more infectious – every COVID infected person can transmit to 5 or 8 people (called the reproductive number and symbolized as R0 5-8) as opposed to the Alpha variant which transmits to 3 to 5 people (R0 3-5), the Delta variant is about 60% more infectious than the original SARS-CoV-2 virus (COVID virus) was. Because of this we will need to have a much higher bar for immunity.
2. The most recent research is shedding new light on the amount of true protection individuals have, from COVID-19 infection, to include the new strains – like Delta. Being vaccinated with two doses of one of the mRNA vaccine offers the strongest protection. Having only one dose of a vaccine is still protective, but to a lesser degree than having received both shots. Lastly, we are seeing that unvaccinated individuals have no meaningful protection and even those who had a previous COVID-19 infection (natural immunity) are only weakly protected, against the newer variants. This will inevitably affect that way that we look at previously infected individuals, and what amount of effective natural immunity they are realistically carrying against the Delta strain, not to mention strains to come. Moving forward for public health estimates we will weigh heavily the effectiveness of both vaccines (mRNA [two doses] and J&J [single dose]) and report separately the percent of individuals who have been vaccinated as well as our COVID case counts.