Pfizer AstraZeneca COVID vaccine antibody levels may decline in 2-3 months: Lancet Study

Total antibody concentrations start to decline in sixth week after complete immunisation with Pfizer and AstraZeneca vaccines. A study presented in Lancet journal on July 15, reported that antibodies wane by more than 50 percent over 10 weeks. In absence of ongoing antibody synsis, antibody concentrations decay at a predictable, exponential rate, explained Professor Eleanor Riley, Immunology and Infectious Diseases, University of Edinburgh, and an author of study.

" levels of antibody following both doses of eir AstraZeneca or Pfizer vaccine were initially very high, which is likely to be an important part of why y are so protective against severe COVID-19," said Mhumita Shrotri from UCL Institute of Health Informatics.

researchers from University College of London (UCL) studied that antibody levels dropping at rate could begin to "wear off protective effects" of vaccines against new variants. However, frequency at which it is to happen is not ascertained in study.  researchers have also noted that antibody levels are substantially higher following two doses of Pfizer vaccine than after both jabs of AstraZeneca preventive, which is called Covishield in India, PTI reported.

According to Lancet study, antibody levels in subjects were initially much higher in vaccinated people than those with before SARS-CoV-2 infection, author and researcher of study Mhumita Shrotri from UCL Institute of Health Informatics said. However, re was a subsequent drop in antibody levels over course of 2-3months, Shrotri ded.

For Pfizer, antibody levels reduced from a median of 7,506 Units per millilitre (U/mL) at 21–41 days, to 3,320 U/mL at 70 or more days. For AstraZeneca vaccine, antibody levels reduced from a median of 1,201 U/mL at 0–20 days to 190 U/mL at 70 or more days, over a five-fold reduction.

'It is not necessarily a problem': Immunologist Prof Riley

Even though re is a subsequent decrease in antibody levels after approximately 6 weeks of getting vaccinated, condition "is not necessarily a problem," clarified Professor Riley. She explained parameters on which antibody concentrations are measured. She also ded that cells take up a process called 'memory response' in face of infections. “ two key parameters are first,  minimum concentration of antibodies required for protection and secondly, how quickly antibody concentrations can increase again in face of infection ( so-called memory response)," she explained.

" decline in antibody concentrations in immediate few weeks after vaccination is exactly what I would expect to see," Professor Eleanor Riley.

While talking about drawbacks of study, she said, "This study does not answer se questions and, indeed, y are perhaps most crucial questions we need to answer in order to determine need for booster doses." As authors mselves say “ clinical implications of waning antibody levels are not yet clear and it remains crucial to establish S-antibody thresholds associated with protection against infection and disease”.

Lower antibody, stronger T-cells

findings were based on data collected from over 600 people aged 18 and above, which were consistent across all groups of people regardless of age, chronic illnesses, or sex, according to researchers. authors highlighted that although clinical implications of waning antibody levels are not yet clear, some decline was expected and current research shows that vaccines remain effective against severe disease.

mRNA vaccines such as Pfizer/BioNTech vaccine are designed to induce high concentrations of antibodies. Viral vectored vaccines (such as Oxford-AstraZeneca vaccine) tend to induce lower antibody responses but stronger T cell responses. differences in antibody concentrations induced by two vaccines are thus not surprising and not a cause for concern. “However, emerging evidence suggests that antibodies are particularly important for blocking infection and preventing onward transmission of virus whereas T cells may be particularly relevant for preventing severe disease and death. Maintaining sufficient antibody concentrations to reduce transmission will be important to limit amount of circulating virus but maybe less important for protection against severe disease," Professor Riley concluded.

(Image input: AP)