Impact of the Delta variant on vaccine efficacy and response strategies

Expert Rev Vaccines. 2021 Oct;20(10):1201-1209. doi: 10.1080/14760584.2021.1976153. Epub 2021 Sep 9.


Introduction: The Delta variant of SARS-CoV-2 has caused a new wave of the COVID-19 epidemic in many countries. It is the most infectious variant of SARS-CoV-2 to date, and its high infectivity means that a higher proportion of the population needs to be vaccinated to reduce the disease burden, which poses a substantial public health challenge.

Areas covered: The evolution of the Delta variant is reviewed, including an overview of the Delta Plus variant with a K417N mutation in the RBD, which may confer an improved immune evasion ability. Decreases in serum neutralizing antibody titers after vaccination against Delta were greater than those against Alpha but less than those against Beta. The protective efficacy of existing vaccines against the Delta variant have declined and is related to the number of doses and the time since vaccination.

Expert opinion: The currently used vaccines are effective against hospitalization/severe disease due to the Delta variant. Accelerating the popularization of vaccination, improving the coverage rate, and the implementation of intervention measures, such as wearing masks, are effective means to control the spread of the Delta variant and other variants. However, vaccination alone against SARS-CoV-2 without intervention measures may lead to continuous spread and the emergence of new variants.

Keywords: SARS-CoV-2; Vaccine; efficacy; neutralization; variant.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Antibodies, Neutralizing / immunology
  • Antibodies, Viral / blood
  • COVID-19 / prevention & control*
  • COVID-19 / virology
  • COVID-19 Vaccines / administration & dosage*
  • COVID-19 Vaccines / immunology
  • Hospitalization / statistics & numerical data
  • Humans
  • Immune Evasion / immunology
  • SARS-CoV-2 / immunology
  • SARS-CoV-2 / isolation & purification*
  • Severity of Illness Index
  • Vaccination / methods


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • COVID-19 Vaccines

Grants and funding

This work was supported by the National Key R&D Program of China (2020YFC0860500).