Washington: A new study shows that two months after the second Pfizer/Moderna vaccination, the antibody response drops by 20 percent in adults with previous cases of COVID-19. The study also tested how well existing vaccines are resistant to emerging variants.
The results of the study were published in the journal Scientific Reports. The Northwestern University study emphasized the importance of receiving a second dose of the vaccine, not only because immunity from vaccines is generally known to wane over time, but also because of the risks posed by emerging variants, including the highly infectious delta variant.
The study also showed that prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor does it guarantee a strong antibody response to the first vaccine dose.
This directly contradicts the assumption that infection with COVID will make a person naturally immune from infection again. The results also support vaccination (and two doses), even for people who have had the virus previously.
A team of scientists, including biological anthropologist Thomas McDaid and pharmacologist Alexis Demonbreun, tested blood samples from adults who tested positive for SARS-CoV-2 to measure how long the immune benefits of the Pfizer and Moderna vaccines last and how well they protect against the newer. variables.
Study participants were drawn from a racially and ethnically diverse community sample of Chicago-area adults who were recruited at the start of the epidemic. Using in-house lab-developed antibody test kits, participants provided blood samples two to three weeks after the first and second dose of vaccination and two months after the second dose.
In the lab, the researchers tested neutralizing antibodies by measuring whether a blood sample could block the interaction between the virus’s spike protein and the ACE2 receptor — that interaction is how the virus causes an infection once it enters the body.
“When we tested blood samples from participants about three weeks after the second vaccine dose, the average level of inhibition was 98 percent, indicating a very high level of neutralizing antibodies,” said McDaid, professor of anthropology at the Weinberg College of Arts and Sciences. Science and Faculty Fellow at the University’s Institute for Policy Research.
The scientists tested the emerging variants B.1.1351 (South Africa), B.1.1.7 (UK) and P.1 (Brazil) and found that the level of inhibition of the viral variants was significantly lower, ranging from 67 percent to 92 percent.
In test samples collected two months after the second dose, they found that antibody responses decreased by about 20 percent. The researchers found that the antibody response to vaccination varies based on a history of previous infection. Individuals with clinically confirmed cases of COVID-19 and multiple symptoms had a higher response level than those who tested positive but had mild or no symptoms.
“Many people and many clinicians assume that any previous exposure to SARS-CoV-2 will confer immunity to re-infection. Based on this reasoning, some people with previous exposure do not think they need to be vaccinated,” she said.
“Or if they are vaccinated, they think they only need the first of two doses of the Pfizer/Moderna vaccine,” McDaid added.
“Our 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,” McDaid continued.
“For people who have had a mild or asymptomatic infection, their antibody response to the vaccination is essentially the same as that of people who have not been exposed before,” McDaid explained. McDaid added that although the research was conducted before the Delta virus emerged, the conclusions are similar.”
In terms of post-vaccination protection, the story is the same for all variants, including delta – the vaccine provides good protection, but not as good protection as the original version of the virus for which the vaccine was designed.”
“Combine that with the fact that immunity wanes over time, you get increased vulnerability to infection. So that’s two shocks now – delta plus weakened immunity between the first wave of vaccinations,” McDaid concluded.