New York,  Breakthrough infections greatly enhance immune response to variants of the virus that causes Covid-19, according to a new study.

The study, published in the Journal of the American Medical Association (JAMA), revealed that a breakthrough infection generates a robust immune response against the Delta variant.

The findings, led by researchers from Oregon Health and Science University (OHSU), suggest the immune response is likely to be highly effective against other variants, including the Omicron variant, as the SARS-CoV-2 virus continues to mutate.

The study is the first to use live SARS-CoV-2 variants to measure cross-neutralisation of blood serum from breakthrough cases.

"You can't get a better immune response than this," said senior author Fikadu Tafesse, Assistant Professor of molecular microbiology and immunology in the OHSU School of Medicine.

"These vaccines are very effective against severe disease. Our study suggests that individuals who are vaccinated and then exposed to a breakthrough infection have super immunity," Tafesse added.

The study found that antibodies measured in blood samples of breakthrough cases were both more abundant and much more effective - as much as 1,000 per cent more effective - than antibodies generated two weeks following the second dose of the Pfizer vaccine.

Vaccine immunity is currently undergoing a real-world test against the new Omicron variant.

"We have not examined the Omicron variant specifically, but based on the results of this study we would anticipate that breakthrough infections from the Omicron variant will generate a similarly strong immune response among vaccinated people," Tafesse said.

The study compared blood samples collected from a total of 52 people, who were vaccinated with the Pfizer vaccine and subsequently enrolled in the study.

A total of 26 people were identified as having mild breakthrough infections following vaccination. Among the sequence-confirmed breakthrough cases, 10 involved the highly contagious Delta variant, nine were non-delta and seven were unknown variants.

The researchers then measured the immune response to the live virus exposed to blood samples from people with breakthrough cases and compared it with the immune response to the control group. They found the breakthrough cases generated more antibodies at baseline, and they found that those antibodies were substantially better at neutralising the live virus.

"The key is to get vaccinated," Curlin said. "You've got to have a foundation of protection."