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Can natural immunity from prior infection protect you from getting COVID again? The answer, like every question throughout this pandemic, is it depends.

A study released in September and published on the CDC website of 72 people on Predictors of Nonseroconversion after SARS-CoV-2 Infection, showed that “Not all persons recovering from severe acute respiratory syndrome coronavirus 2 develop SARS-CoV-2–specific antibodies.”

This means that the level of antibodies after infection depends on numerous factors, including a patient’s immune system, age, health history and viral load of SARS-CoV-2 in their nose.

The study showed that 36 percent of participants were seronegative even with testing on three samples each, for IgA, IgM, and IgG against multiple  SARS-CoV-2 antigens and neutralizing antibodies.

This is why the CDC and WHO recommend vaccination even after recovery from COVID-19.

To measure IgA, IgM, and IgG antibodies, labs like Lifescan Labs in Skokie, Illinois use a SARS-CoV-2 antibody or serology test. This test measures the antibodies in a blood sample to determine if an individual has had a past infection with the virus that causes COVID-19 or antibodies from vaccination. These types of tests cannot be used to diagnose a current infection.

In another, earlier study released in Nov. 2020 of a real-world sample, “Among 156 frontline healthcare personnel who had positive SARS-CoV-2 antibody test results in spring 2020, 94 percent experienced a decline at repeat testing approximately 60 days later, and 28 percent seroreverted to below the threshold of positivity.”

In late August 2021, a study released from Israel showed that those who recovered from prior infection were less likely to be reinfected by the Delta variant than those who were vaccinated. It’s the largest real-world observational study so far to compare natural and vaccine-induced immunity to SARS-CoV-2. Importantly, the study also showed that those who had prior infection, combined with at least one vaccine, were even better protected from Delta, as well as hospitalization and death. 

Science Magazine reports on the Israeli study, saying, “The natural immune protection that develops after a SARS-CoV-2 infection offers considerably more of a shield against the Delta variant of the pandemic coronavirus than two doses of the Pfizer-BioNTech vaccine, according to a large Israeli study that some scientists wish came with a ‘Don’t try this at home’ label. The newly released data show people who once had a SARS-CoV-2 infection were much less likely than never-infected, vaccinated people to get Delta, develop symptoms from it, or become hospitalized with serious COVID-19.”

The study is obviously not a green light to go out and “let her rip” or plan a COVID infection party because the risk of contracting COVID can result in severe disease, symptoms of long COVID or death.

Widespread vaccination is key to controlling the pandemic and avoiding mutation into a new variant that evades the vaccines.

The Israel study, however, is an important one to show that natural immunity is real and should be a factor considered in public health decisions.


Only serology testing can indicate each person’s antibody levels

At Lifescan Labs, based in Skokie, Ill., we’ve invested heavily in our ability to perform COVID antibody tests for anyone who needs one. Testing the level of antibodies is key to making the best decision for each patient’s health, especially for immunocompromised individuals.

For most people following an infection, binding and neutralizing antibodies develop within 1–3 weeks after the onset of symptoms, and titers correlate with disease severity.

Testing the level of antibodies is one key way to know how well protected an individual is from having a severe outcome to a reinfection of COVID. For some patients with compromised immune systems due to past or present illnesses, says Dr. Sam Lipshitz, medical director at Lifescan Labs, antibodies can dip below a healthy number even after double vaccination. These patients are eligible for a booster.


Here’s how serology testing at Lifescan Labs works

Lifescan Labs performs the serology/immunology assay of SARS-Cov-2-IGG antibodies using the ABBOTT Advise DX SARS-CoV-2 assay methodology with an automated, state-of-the-art instrumentation also by Abbott Diagnostics. This test has been authorized for emergency use by the FDA (under an EAU) for use only by accredited laboratories.

Our laboratory in Skokie, Ill. performs this test every day, and results are available within a few hours from time of sample receipt in the laboratory to final results.

We are also able to draw blood samples on-site from individual patients.

While there is no pre-testing preparation required prior to blood sample collection, regulatory experts highly recommend that samples should be tested from individuals who have indicated a prior or recent COVID-19 infection of 15 days or more post symptom onset. For some people, the test is used to measure antibody levels after receiving the vaccine.

The end point reading of the test is reported quantitatively from a minimum reportable range of 50 to greater than 25,000 A/units, and recovered values are solely dependent on the person’s immune bodily response. Each individual result varies widely.

Values of 50 A/units or more indicates a POSITIVE IGG level, due to immunologic response to the spike protein of the SARS-Cov-2 virus. Healthcare professionals may use this information as an aid in determining a person’s current immunity status for those who have previously or recently been infected with COVID-19 and recovered or who have received the vaccine.

Results are available directly to the individual (or patient) and may be forwarded to their own healthcare professional for proper interpretation and guidance. 

On a weekly basis, we process around 25 serology tests to measure antibody levels in patients.

The serology test measures spike antibodies  levels, and anything between 50 and 25,000 offers good protection against severe hospitalization or death from a breakthrough infection of COVID-19.


Natural immunity combined with vaccination is a powerful shield against COVID-19

Natural immunity alone cannot control the spread of COVID-19, as evidenced by countries like Iran and Brazil, where higher rates of infection haven’t led to more immunity. Of course, natural immunity is less predictable than vaccination, which is standardized and longer lasting.

The CDC and the WHO both recommend an mRNA vaccination after COVID infection, once an individual recovers. Vaccination, combined with natural immunity, significantly reduces the likelihood of reinfection with a severe outcome of hospitalization or death.


How much do waning antibodies matter?

While immunological studies have shown that antibodies wane after natural infection and after vaccination, what’s less clear is how long immunity against severe disease lasts. That’s because antibodies are one line of defense against contracting and having a severe response to COVID-19. In addition to antibodies, the body is protected by Memory B cells and T cells, which can provide people with durable immunity.

Dr. Lipshitz explains how our bodies also protect us with an army of Memory B cells and T cells. “The body can develop a system to defeat the invaders or at least mobilize it so that you can survive the attack.”

John Wherry, an immunologist at the University of Pennsylvania Perelman School of Medicine in Philadelphia, who led a study described in Nature, says, “Circulating antibodies may be declining, but your immune system is capable of jumping into action once again.”

This is good news for the battle against COVID, but it’s making for heated debate about boosters, as well as world-wide vaccine equity.

What’s interesting, says Dr. Lipshitz, is “this is the first time I can remember in my history of practicing medicine that patients needed this level of awareness of immunology. Now everybody’s trying to be the boss. This has affected our day-to-day lives as a society.”

In general, Memory B cells quietly circulate in the bloodstream, sometimes for decades, and serve to memorize the characteristics of the original antigen that activated their parent B cell during initial infection. If these Memory B cells meet up with the particular antigen again, they’re trained to jump into action. 

As for T cells, they act as the heavy armor of your immune system. When your body encounters SARS-CoV-2, and it slips through the first line of antibody defense, these Memory B-cells and T-cells are ready for battle. 

This is the basics for how vaccines work — patients get a small, harmless amount of protein from a disease to allow the immune system to recognize that protein in the future if the pathogen were to invade the body. 

When it comes to SARS-CoV-2, Penn Medicine researchers analyzed the T-cell responses in 47 healthy people who received two doses of the Moderna and Pfizer/BioNTech mRNA vaccines.

“The results reveal the complex details of how the T-cell response to these vaccines unfolds, and underline the importance of a second dose for people with no history of COVID-19. The findings showed, however, that in people with a history of COVID-19, the T-cell response was already robust after the first vaccine dose, with no significant increase after the second dose, which may have implications for potential future booster shots.”

The response of T-cells to vaccines are harder to study than antibody responses, so less is known about those responses, including in the case of COVID-19.

Studies throughout the pandemic are coming in fast and furious, and many have yet to be peer reviewed, for obvious reasons. However, at this point, both real-world data and laboratory studies have shown that natural immunity immunity and vaccination offer a formidable shield against serious disease and death from COVID-19. The level of the antibodies for each person, though, vary. That’s what serology testing is for.

For more information about serology testing at your organization or facility, contact us here