People vaccinated three times or immunised after an earlier COVID-19 infection have comparable neutralising antibody response to those with a breakthrough infection, according to a study.
A breakthrough infection is a case of illness in which a fully vaccinated individual becomes infected.
The study, published in the journal Cell, looked at the strength, durability and breadth of neutralising antibody response generated by breakthrough infections in individuals vaccinated against SARS-CoV2.
The researchers at the University of Washington in the U.S. noted that the Delta and Omicron coronavirus variants have enhanced transmissibility and immune evasion compared to the original virus.
These characteristics, and the waning of immunity from vaccines, have led to breakthrough infectionsin vaccinated individuals, they said.
The study found that the degree of antibody response depended on whether a person has had one, two, three, or four exposures to the spike protein through infection, vaccination, or a mixture of the two.
The spike protein is used by the SARS-C0V-2 virus to enter and infect cells.
The researchers checked antibody response in a group of individuals who had been vaccinated after having COVID-19.
They also analysed the antibodies in people who were previously vaccinated and experienced a breakthrough infection, those who were vaccinated only, and individuals who were boosted.
The team found that people who had received three-vaccine doses, those vaccinated after recovering from COVID-19, and those with a breakthrough infection had almost comparable neutralising antibody responses, in terms of magnitude and breadth.
Their blood serum binding and antibody neutralising responses to the spike protein in the coronavirus variants were much more potent and lasting than those generated by people who had received only two doses of vaccine.
This observation suggested that the increased number of exposures to SARS-CoV-2 antigens, either through infection and vaccination or triple vaccination, enhanced the quality of antibody responses, the researchers said.
They also investigated neutralisation of the divergent Omicron SARS-CoV-2 variant of concern that is driving the current wave of infections globally.
Their findings showed that boosted individuals had neutralising antibodies at similar levels to subjects vaccinated twice against the original ancestral strain.
This suggests a large amount of immune evasion, but that vaccine boosters can help close the neutralising antibody gap caused by Omicron, the researchers added.
