The coronavirus Gamma variant, officially known as P.1, was a specific lineage of SARS-CoV-2, the virus responsible for COVID-19. It emerged during the global pandemic as one of several variants that acquired genetic changes, distinguishing it from earlier versions of the virus. The World Health Organization classified it as a “variant of concern” due to its potential implications for public health.
Origin and Naming
The Gamma variant was first identified by Japan’s National Institute of Infectious Diseases on January 6, 2021, in four travelers from Amazonas, Brazil. It was confirmed to be circulating widely in Brazil, particularly in Manaus, causing a significant surge in infections in early 2021.
Scientifically, this variant is designated P.1, a descendant of the B.1.1.28 lineage. The World Health Organization (WHO) assigned it the label “Gamma variant” as part of a scheme to use Greek letters for variants of concern. This designation reflected its potential for increased transmissibility, more severe disease, or reduced effectiveness of vaccines and treatments.
Key Characteristics and Concerns
The Gamma variant possessed 17 amino acid substitutions, with ten located in its spike protein, including the N501Y, E484K, and K417T mutations. The N501Y mutation, also found in other variants like Alpha, was associated with an increased binding affinity to the human ACE2 receptor, potentially enhancing the virus’s ability to infect cells.
The E484K mutation, present in Gamma and Beta variants, was linked to reinfection and could reduce the neutralizing activity of antibodies from vaccination or previous infection. Studies suggested that the Gamma variant could be 1.7 to 2.4 times more transmissible than earlier SARS-CoV-2 strains. Some research indicated that P.1 infected individuals had a greater chance of death compared to those infected with the B.1.1.28 lineage.
Effectiveness of Vaccines and Treatments
COVID-19 vaccines generally demonstrated effectiveness against the Gamma variant, particularly in preventing severe disease, hospitalization, and death. For instance, a single dose of the Oxford/AstraZeneca vaccine was 82% effective against hospitalization or death caused by Beta or Gamma variants. Full vaccination effectiveness against Gamma was estimated around 72–82%.
The Gamma variant’s mutations, especially E484K, raised concerns about reduced neutralizing antibody activity, which could affect some therapeutic treatments like monoclonal antibodies. Monoclonal antibody therapies reduced hospitalizations and deaths, but their effectiveness against Gamma varied. Some treatments, such as casirivimab, showed reduced effectiveness against Gamma compared to earlier strains.
Global Spread and Subsequent Decline
Following its detection in Brazil, the Gamma variant spread to numerous countries worldwide, verified in 98 locations by December 2021. It caused widespread infection in Brazil, particularly in Manaus, where it rapidly replaced previous lineages.
The Gamma variant eventually declined in global dominance. This was largely attributed to the emergence and rapid spread of newer, more transmissible variants like Delta and Omicron. These later variants displaced Gamma, becoming the predominant circulating strains. By March 2022, the Gamma variant was largely supplanted by Delta and Omicron variants.