A research published in The Lancet journal has found that the total antibody levels start to become weaker six weeks after completing immunisation with Pfizer and AstraZeneca vaccines. The antibody levels may also be reduced by more than 50 per cent over 10 weeks or 2-3 months.
The researchers from University College London (UCL) in the UK noted that if the antibody levels carry on dropping at this rate, there are concerns that the protective effects of the vaccines may also begin to wear off, particularly against new variants. However, they said, how soon that might happen cannot be predicted yet. The UCL Virus Watch study also found that antibody levels are substantially higher following two doses of the Pfizer vaccine than after two shots of the AstraZeneca preventive, known as Covishield in India.
Antibody levels were also much higher in vaccinated people than those with prior SARS-CoV-2 infection, they said. "The levels of antibody following both doses of either the AstraZeneca or Pfizer vaccine were initially very high, which is likely to be an important part of why they are so protective against severe COVID19," said Madhumita Shrotri from UCL Institute of Health Informatics. "However, we found these levels dropped substantially over the course of two to three months," Ms. Shrotri said in a statement.