Delta (B.1.617.2), Vaccine Effectiveness & Intranasal Vaccines: Microbial Minutes

Aug. 19, 2021

Are breakthrough infections more common with Delta? Why are fully vaccinated people still transmitting the virus? Could intranasal vaccines block transmission? What can be done to stop viral evolution?

What's Hot in the Microbial Sciences?

ASM presents Microbial Minutes, a monthly video series of trending topics in the microbial sciences.

Recent surges of COVID-19 as a result of the Delta variant’s rapid spread have caused mixed feelings of discouragement, fear and denial across the globe. Healthcare workers are once again feeling the strain as hospitals are flooded with COVID-19 cases. And the CDC has recommended masking in indoor public spaces, regardless of vaccination status, in areas where COVID-19 transmission is high. 

People are questioning whether vaccines are still working. And if so, why we need to wear masks again. We dissect the research that will help address those questions. 

Will Vaccines Remain Protective Against the Delta Variant?

How Dangerous is the Delta Variant (B.1.617.2)?

Stowe J. et al. "Effectiveness of COVID-19 vaccines against hospital admission with the Delta (B.1.617.2) variant." 2021

Venkata-Viswanadh E. et al. "Infection and Vaccine-Induced Neutralizing-Antibody Responses to the SARS-CoV-2 B.1.617 Variants." New England Journal of Medicine. Aug. 12, 2021.

Are Breakthrough Infections More Common With Delta?

Gupta N. et al. "Clinical characterization and Genomic analysis of COVID-19 breakthrough infections during second wave in different states of India." medRxiv. July 15, 2021.

Brown C.M. et al. "Outbreak of SARS-CoV-2 Infections, Including COVID-19 Vaccine Breakthrough Infections, Associated with Large Public Gatherings — Barnstable County, Massachusetts, July 2021." Morbidity and Mortality Weekly Report. Aug. 6, 2021.

Why Are Fully Vaccinated People Still Transmitting the Virus?

Ying Chia P. et al. "Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study." medRxiv. July 31, 2021.

Matheson N.J. et al. "How does SARS-CoV-2 cause COVID-19?" Science. July 31, 2020.

Sheikh-Mohamed S. et al. "A mucosal antibody response is induced by intra-muscular SARS-CoV-2 mRNA vaccination." medRxiv. Aug. 4, 2021.

Could Intranasal Vaccines Help Block Transmission?

India's Bharat Biotech's nasal COVID-19 vaccine advances into next stage of trials

van Doremalen N. et al. "Intranasal ChAdOx1 nCoV-19/AZD1222 vaccination reduces viral shedding after SARS-CoV-2 D614G challenge in preclinical models." Science Translational Medicine. Aug. 18, 2021.

An D. et al. "Protection of K18-hACE2 mice and ferrets against SARS-CoV-2 challenge by a single-dose mucosal immunization with a parainfluenza virus 5–based COVID-19 vaccine." Science Advances. July 2, 2021.

Take-Away Points

  • The Delta variant is 40-60% more transmissible than Alpha and almost twice as transmissible as the original Wuhan strain.
  • Vaccines remain highly effective at preventing hospitalization and death from Delta infection.
  • Data indicate that vaccinated individuals may still be able to transmit the virus. 
  • This is due, in part, to the generation of insufficient mucosal immunity via systemic injection to remain protective long term.
  • Mucosal routes of immunization are under investigation, with a number of intranasal vaccines entering clinical trial. 
  • In combination, vaccination and masking can reduce the risk of severe disease, slow transmission and reduce the evolution of SARS-CoV-2.

Author: Ashley Hagen, M.S.

Ashley Hagen, M.S.
Ashley Hagen, M.S. is the Scientific and Digital Editor for the American Society for Microbiology and host of ASM's Microbial Minutes.