Rapid emergence and spread of the gamma variant in Haiti

Clinician with a collection vial to test for the new variant  of the coronavirus strain called the gamma variant.
Illustration of a collection vial for genetic viral variant testing. (Credit: Stock)

Researchers are learning more about how people who have immunity—either through natural infection or vaccination—respond to freshly emerging variants of the SARS-CoV-2 virus which causes COVID-19. New data from Haiti demonstrates how a largely unvaccinated population that had widespread past exposure to earlier lineages of the virus was still susceptible to a new wave of illness driven by a genetic variant.

The gamma variant, also known as variant of concern P.1, first emerged in the fall of 2020 in Brazil. The severity of the P.1 outbreak in Manaus took many people by surprise because the city had already seen a huge wave of COVID-19 infections from earlier SARS-CoV-2 lineages.  It had been hoped that natural immunity generated from the original surge of cases would protect people from subsequent infection. That did not happen, and the city experienced a major second surge of illness.

New data from Haiti retrospectively reveals a similar scenario. In work published today in Clinical Infectious Diseases, UF researchers report the findings from seropositivity (blood tests) and genetic sequencing analyses over time in Haiti which reveal how the P.1 genetic variant spread rapidly nearly a year after an initial wave of COVID-19.

The first epidemic wave swept through the island in the summer of 2020. Findings from blood tests indicated about 40% of the population had been exposed at that time, the researchers write. After the initial peak, cases in Haiti remained at a generally low level until April 2021, when there was a sudden, striking increase in case numbers. Genetic sequencing showed that this surge of cases was caused by the new introduction of the gamma (P.1) variant into Haiti. Once introduced, this variant expanded exponentially and rapidly replaced other lineages that had been circulating in the population.

“Our data highlight the profound impact that a highly transmissible variant such as P.1 can have when introduced into a new area,” said Glenn Morris, M.D., M.P.H & T.M., Director of the UF Emerging Pathogens Institute and one of the co-authors of the study. “There has been the belief that prior exposure to early lineages of SARS-CoV-2 would protect a population from such introductions. However, as seen with the gamma variant in this instance, and as seen in the United States with the recent introduction of the delta variant, these variants have the ability to rapidly spread in a region where there have been numerous prior COVID cases.”

The study authors note that the rapid expansion of gamma variant cases in Haiti occurred in a setting in which there had been minimal administration of COVID vaccines. While the appearance of variants such as gamma and delta in a new population is of major concern, vaccination continues to be a key element in control of the disease.

Contributing authors from UF include Massimiliano S Tagliamonte, Carla Mavian, Melanie Cash, Britanny Magalis, Marco Salemi, and Glenn Morris (UF College of Medicine/EPI); John Lednicky (UF College of Public Health and Health Professions/EPI); and Alberto Riva (UF Interdisciplinary Center for Biotechnology Research).

Written by: DeLene Beeland