Two forms of immunity -- breakthrough infections following vaccination or natural infection followed by vaccination -- provide roughly equal levels of enhanced immune protection, finds a study.
The study, published online in the journal Science Immunology, found that in both cases, the immune response measured in blood serum revealed antibodies that were equally more abundant and more potent -- at least 10 times more potent -- than immunity generated by vaccination alone.
"It makes no difference whether you get infected and then vaccinated, or if you get vaccinated and then a breakthrough infection," said Fikadu Tafesse, Assistant Professor of molecular microbiology and immunology in the Oregon Health & Science University's School of Medicine.
"In either case, you will get a really, really robust immune response -- amazingly high," Tafesse added.
Although the study was done before the emergence of the highly transmissible omicron variant, researchers expect the hybrid immune responses would be similar.
"The likelihood of getting breakthrough infections is high because there is so much virus around us right now," Tafesse said.
"But we position ourselves better by getting vaccinated. And if the virus comes, we'll get a milder case and end up with this super immunity."
Researchers recruited a total of 104 people, all who were vaccinated by the Pfizer vaccine, and then carefully divided them into three groups: 42 who were vaccinated with no infection, 31 who were vaccinated after an infection, and 31 who had breakthrough infections following vaccination.
Controlling for age, sex and time from vaccination and infection, the team drew blood samples from each participant and exposed the samples to three variants of the live SARS-CoV-2 virus.
They found both of the groups with "hybrid immunity" generated greater levels of immunity compared with the group that was vaccinated with no infection.
With the wildly contagious Omicron variant now circulating across the globe, the new findings suggest each new breakthrough infection potentially brings the pandemic closer to the end.
"I would expect at this point many vaccinated people are going to wind up with breakthrough infections -- and hence a form of hybrid immunity," said senior co-author Bill Messer, Assistant Professor of molecular microbiology and immunology, and medicine (infectious diseases) in the OHSU School of Medicine.
Over time, the virus will run into an ever-expanding pool of human immunity.
With the spread of the highly contagious Omicron variant, many unvaccinated people who were previously infected are likely to confront the virus again.
For that group, previous research reveals a much more variable level of immune response than vaccination, Messer said.