Total antibody levels start to decline after six weeks of complete immunisation by AstraZeneca and Pfizer vaccines, according to a study published by the Lancet Journal. The study claims that antibody levels further decline by over 50% in the next 10 weeks. There have been concerns about the protective effects of the vaccine wearing off against new variants if the antibody levels wane at this rate. However, it is still unclear when that might happen.

The UCL Virus Watch study further discovered that antibody levels after two shots of Pfizer are higher than those after two doses of AstraZeneca, known as Covishield in India.

Furthermore, antibody levels in vaccinated people were much higher than the ones already infected by SARS-CoV-2, they said.

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“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 COVID-19,” said Madhumita Shrotri from UCL Institute of Health Informatics in a statement.

She added, “However, we found these levels dropped substantially over the course of two to three months.”

As per research, the data was collected from close to 600 people aged 18 and above. The findings were consistent across all groups of people regardless of age, chronic illnesses or sex. It was deduced that vaccines remained effective against severe diseases.

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“When we are thinking about who should be prioritised for booster doses our data suggests that those vaccinated earliest, particularly with the AstraZeneca vaccine, are likely to now have the lowest antibody levels,” said Professor Rob Aldridge from UCL Institute of Health Informatics. As it was found that those immunised with the Pfizer vaccine had higher antibody levels than those vaccinated with AstraZeneca’s, Mr Aldridge pointed out that this should be considered when boosters are rolled out.

As of now, further research is imperative to determine whether there is an antibody level threshold required for immunity against severe disease.