The Delta variant of SARS-CoV-2 now accounts for >20% of new US infections and WHO estimates is has spread to 96 countries. We summarize current data and perspective.
The SARS-CoV-2 Delta variant (formerly B.1.617.2), assessed to be more highly transmissible than the original virus, has been detected in 96 countries, according to the World Health Organization, and in the US has quickly become the cause of >20% of new cases of infection.
Vaccines currently available do appear to protect against infection with Delta and related hospitalization but public health authorities remain cautious.
All health officials agree that it is the unvaccinated who are at significant risk from this opportunistic variant, a reality now devastating the Indian continent. In the US, the greatest concern is for states in the south and southwest where vaccination rates lag far behind the country as a whole.
Click through our summary of the current impact of the Delta variant and perspective on how and why that will change.
CDC Variants of Concern: Alpha, Beta, Gamma. Spread more easily; potential reduction in neutralization by some EUA mAB treatments; potential reduction in neutralization by post-vaccination or infection sera.
CDC Variants of Concern: Epsilon, Delta. Spread more easily; potential reduction in neutralization by some EUA mAB treatments; potential reduction in neutralization by post-vaccination or infection sera.
Delta Basics. First Identified: India December 2020. First identified in the US: March 2020. CDC upgrade to Variant of Concern June 14, 2021.
Delta US spread. CDC: The Delta variant at the end of June made up >20% US cases and essentially that number had doubled over 2 weeks.
Delta: The globe. WHO: "As of 29 June 2021, 96 countries have reported cases of the Delta variant, though this is likely an underestimate as sequencing capacities needed to identify variants are limited. A number of these countries are attributing surges in infections and hospitalizations to this variant."
Delta: The UK. Public Health England. On June 18, Public Health England reported that Delta accounted for 99% of all new coronavirus cases in the country, up from 90% the previous week. PHR research has also suggested that Delta “is associated with an approximately 60 percent increased risk of household transmission compared to the Alpha variant,” and that the number of new cases was doubling every 4.5 to 11.5 days in regions where Delta was spreading.
Delta UK Most Vulnerable. A recent UK study showed that children and adults aged <50 years were 2.5x more likely to become infected with SARS-CoV-2 Delta.
Delta: Other countries. Delta may hamper EU progress against the coronavirus. Cases increasing in Italy, Belgium. In Portugal, now accounts for 60% of new cases in Lisbon. In Russia, now accounts for ~90% of all new cases in Moscow, now enduring significant outbreak. In Indonesia Delta is already dominant in some locales, including Jakarta. Less than 5% of ~270 million Indonesian residents have been fully vaccinated as of mid-June.
Delta: "Faster, Fitter." The Delta variant “is faster, it is fitter, [and] it will pick off the more vulnerable more efficiently than previous variants. And therefore, if there are vulnerable people left without vaccination, they remain even at further risk." Michael J Ryan, MPH, MB BCh, BAO, Executive director, WHO Emergencies Program, WHO press conference, June 21, 2021.
Delta: WHO says: "Masks." WHO officials, on June 25, 2021, urged fully vaccinated people to continue to wear masks and practice other COVID-19 pandemic safety measures as the highly contagious Delta variant spreads rapidly across the globe. “People cannot feel safe just because they had the two doses. They still need to protect themselves.” Dr. Mariangela Simao. WHO Assistant Director General for Access to Medicines, Vaccines and Pharmaceuticals. WHO press conference, June 25, 2021.
Delta: CDC says: "Masks are local." WHO mask recommendations are made in the context of a global vaccination rate of <15%, says CDC director Rochelle Walensky. CDC says, given overall US vaccination status, guidelines from local policy makers that are based on local COVID-19 conditions should guide current US practice. “There are areas of this country where about a third of people are vaccinated” and so “have more disease.” “…masking policies are not to protect the vaccinated, they are to protect the unvaccinated.” Rochelle Walensky, MD, MPH, Director, US Centers for Disease and Prevention, during network television interviews week of June 28, 2021.
Delta: Epidemiologic Perspective. "It’s actually quite dramatic how the growth rate will change. Delta is spreading 50% faster than Alpha, which was 50% more contagious than the original strain of SARS-CoV-2—making the new variant 75% more contagious than the original." F. Perry Wilson, MD, MSCE, Associate Professor, Yale Medicine Epidemiology.
Delta: Exponential Spread. “Because of the math, it grows exponentially and more quickly. So, what seems like a fairly modest rate of infectivity can cause a virus to dominate very quickly—like we’re seeing now. Delta is outcompeting everything else and becoming the dominant strain.” F. Perry Wilson, MD, MSCE, Associate Professor, Yale Medicine Epidemiology
Delta: The US South. Vaccination rates lag significantly in southern states, placing the unvaccinated at high risk for infection with Delta. The CDC estimates that, as of June 30, 2021, 46.7% of the US population was fully vaccinated and 54.4% had received 1 dose. Compared with the 5 US states with the lowest percentage of fully vaccinated individuals:
Delta: Vaccine Efficacy. Public Health England research. Pfizer-BioNTech: 88% effective against symptomatic disease, 96% effective against hospitalization. Oxford-AstraZeneca: 60% effective against symptomatic disease, 93% effective against hospitalization. Moderna COVID-19 vaccine produced neutralizing titers against all variants tested, including Delta. Studies tracked participants who were fully vaccinated with both recommended doses.