Washington: People who are infected after getting vaccinated develop a greatly enhanced immune response to variants of the SARS-CoV-2 virus that causes COVID-19, according to a lab study.

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

The findings suggest that the immune response in such people is likely to be highly effective against other variants as the SARS-CoV-2 virus continues to mutate.

“You can’t get a better immune response than this. These vaccines are very effective against severe disease,” said study senior author Fikadu Tafesse, an assistant professor at Oregon Health & Science University (OHSU) in the US.

“Our study suggests that individuals who are vaccinated and then exposed to a breakthrough infection have super immunity,” Tafesse said.

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 – than antibodies generated two weeks following the second dose of the Pfizer vaccine.

The results suggest each exposure following vaccination actually serves to strengthen immune response to subsequent exposures even to new variants of the virus.

“I think this speaks to an eventual end game. It doesn’t mean we are at the end of the pandemic, but it points to where we are likely to land,” said study co-author Marcel Curlin, an associate professor at OHSU School of Medicine.

“Once you are vaccinated and then exposed to the virus, you are probably going to be reasonably well-protected from future variants,” Curlin said.

The study implies that the long-term outcome is going to be a tapering-off of the severity of the worldwide epidemic, the researchers said.

Vaccine immunity, they said, 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, all employees of OHSU who were vaccinated with the Pfizer vaccine and subsequently enrolled in the study.

A total of 26 people were identified through testing 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 immune response to live virus exposed to blood sampled 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 those antibodies were substantially better at neutralising the live virus.

The study underscores the fact that vaccination remains the key to ending the pandemic.

“The key is to get vaccinated. You have got to have a foundation of protection,” Curlin added.

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