Countries worldwide had previously suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an “immunity passport” or “risk-free certificate”. World Health Organization, however, had argued that there was no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection. Now the latest study conducted by the researchers at Northwestern University in the US has found that recovering from the COVID-19 “doesn’t guarantee” antibodies or confer immunity to re-infection.
Scientists analyzed the data from the participants two months after they received their second Pfizer/Moderna vaccine shots and found that the antibody response decreased by nearly 20 percent in adults with prior cases of COVID-19. The study also tested how well current vaccines resist the emerging variants such as the Delta variant in triggering protection. Researchers undermined the importance of administering the second dose of the COVID-19 vaccine, stressing that not only does the immunity from vaccines “wanes over time,” but also there’s an increased risk of infection posed by emerging variants, including the highly contagious delta variant.
Prior exposure to the SARS-CoV-2 that caused COVID-19 respiratory ailment “does not guarantee a high level of antibodies, nor does it guarantee a robust antibody response to the first vaccine dose,” the study highlighted. Scientists contradicted the myth that contracting COVID will naturally make the recovered patient immune to re-infection. The findings were similarly applicable to those who received two doses of the COVID-19 vaccine as it does not provide immunity to reinfection, and therefore, governments worldwide have outlined the importance of adhering to the health safety measures such as masking. This is true even for people who have contracted the virus previously.
Biological anthropologist Thomas McDade and pharmacologist Alexis Demonbreun, tested blood samples from adults who had tested positive for SARS-CoV-2 to measure how long the immunity benefits of Pfizer and Moderna vaccines last. They also analyzed the level of antibodies and their impact on the newer COVID-19 variants. For this, a sample of Chicago-area adults was recruited. Participants submitted blood samples two to three weeks after their first and second dose of vaccination and two months after the second dose.
“Individuals with clinically confirmed cases of COVID-19 and multiple symptoms had a higher level of response than those who tested positive but had mild symptoms or were asymptomatic,” the study published by the Northwestern university found.
“When we tested blood samples from participants collected about three weeks after their second vaccine dose, the average level of inhibition was 98 percent, indicating a very high level of neutralizing antibodies,” said McDade, professor of anthropology in the Weinberg College of Arts and Sciences and a faculty fellow with the University’s Institute for Policy Research.
In the labs, researchers tested for the neutralizing antibodies by measuring whether the blood sample could inhibit the interaction between the virus’ spike protein and the ACE2 receptor – this interaction is how the virus causes an infection once it enters the body. Scientists tested the emerging variants B.1.1351 (South Africa), B.1.1.7 (UK) and P.1 (Brazil) in the blood samples and found the level of inhibition to viral variants was significantly lower, ranging from 67 percent to 92 percent. Just two months after the second dose of the vaccine, the antibody responses declined by about 20 percent, the study found.
“Many people, and many doctors, are assuming that any prior exposure to SARS-CoV-2 will confer immunity to re-infection. Based on this logic, some people with prior exposure don’t think they need to get vaccinated. Or if they do get vaccinated, they think that they only need the first dose of the two-dose Pfizer/Moderna vaccines,” McDade said.
But study shows that prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor does it guarantee a robust antibody response to the first vaccine dose.