A new laboratory study from Oregon Health & Science University (OHSU) suggests more than one path toward strong COVID-19 immunity.

According to the study, two types of immunity - breakthrough infections after vaccination or natural infection followed by vaccination - produce essentially equivalent amounts of increased immune protection.

"It makes no difference whether you get infected and then vaccinated, or if you get vaccinated and then a breakthrough infection," senior co-author Fikadu Tafesse, Ph.D., assistant professor of molecular microbiology and immunology in the OHSU School of Medicine, said. "In either case, you will get a really, really robust immune response - amazingly high."

The study follows an OHSU study published in December that described extremely high levels of immune response following breakthrough infections - so-called "super immunity." That study was the first to measure cross-neutralization of blood serum from breakthrough cases using multiple live SARS-CoV-2 variants.

It doesn't matter whether someone gets a breakthrough illness or is vaccinated after a normal infection, according to a recent study. Immune responses evaluated in blood serum in both cases indicated antibodies that were similarly plentiful and strong - at least 10 times more potent - than immunity induced only by vaccination.

Researchers gathered a total of 104 people, all of whom were OHSU employees who were vaccinated with the Pfizer vaccine, and divided them into three groups: 42 people who were vaccinated without infection, 31 people who were vaccinated after infection, and 31 people who had breakthrough infections after vaccination.

The researchers took blood samples from each participant and exposed them to three forms of the live SARS-CoV-2 virus in a Biosafety Level 3 lab on the OHSU Marquam Hill campus, controlling for age, sex, and time since vaccination and infection.

They discovered that both groups with "hybrid immunity" had higher levels of immunity than the control group.

The research was conducted prior to the emergence of the Omicron variant, but researchers anticipate that the hybrid immunological responses will be comparable to the new variant.

With the highly contagious omicron variety already circulating around the world, the new findings suggest that each new breakthrough infection might bring the pandemic to an end.

OHSU scientists said they haven't studied numerous rounds of natural infection, but considering that millions of people in the U.S. and around the world are completely unvaccinated, many people will likely fall into that category. With the introduction of the extremely contagious Omicron, many previously afflicted unvaccinated people are likely to be infected again.

The virus will eventually encounter an ever-expanding reservoir of human immunity.

Over time, the virus will run into an ever-expanding pool of human immunity.

The study was published online in the journal Science Immunology.