Total antibody levels start to drop six weeks after complete immunisation with Pfizer and AstraZeneca vaccines, according to study published in The Lancet journal. The study adds the levels can reduce by more than 50 per cent over 10 weeks.
The findings based on data from over 600 people aged 18 and above were consistent across all groups of people regardless of age, chronic illnesses or sex.
The researchers from University College London (UCL) warned protective effects of the vaccines may also begin to wear off, particularly against new variants if the antibody levels carry on dropping at this rate.
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.
Further, the study showed that antibody levels were much higher in vaccinated people than those with prior SARS-CoV-2 infection.
The findings support recommendations that adults who are clinically vulnerable, or those aged 70 years or over should be prioritised for booster doses