The Emergence of Delta as the Predominant Strain

The delta variant has replaced the alpha variant as the predominant strain in COVID-19 cases in the United States.

The evolution of delta as the dominant strain in the US has been quick. Contagion Editor-in-Chief Jason Gallagher points out that it accounted for just 5% of cases here in May, and has increased to over 90% of cases in July.

Back in the spring, India was decimated by the delta variant. The country reported over 300,000 cases on a single day alone in May. At one point, the country was losing 3000 people daily to COVID-19. India’s official death toll is more than 414,000, but the statistic has been called into question recently as some have reported the mortality number should be much higher.

Although the US overall has a much higher vaccination rate now than India did in the spring, there are states with lower rates and it is greatly affecting the COVID-19 incidence rates there as well as hospitalizations. The south, and in particular Florida and Texas, have seen the greatest increases.

Contagion spoke with Gallagher about the delta variant including “the fitness of the strain,” how the vaccination rates have affected the surge, and the greater incidence rates of breakthrough infections that the Centers for Disease Control and Prevention reported from its study, which was released last week.