AstraZeneca, Pfizer COVID vaccine antibodies start declining after 10 weeks, says Lancet study

While world leaders continue to put focus on getting the whole population vaccinated against COVID-19 as new variants of coronavirus continue to emerge, how long do we remain safe after receiving two doses? A new Lancet study said that if a person has received Pfizer or AstraZeneca, the total antibody levels start to wane six weeks after complete immunisation and it can further decline by 50 percent over 10 weeks, study said.  

If antibodies, which give protection from COVID-19, level start decreasing at this rate, the researchers said then it raises concerns over the protective effects of the vaccines on the person. They said that the effects of the vaccine may also start wearing off, especially in protection from new COVID variants. The researchers from University College London (UCL) in the UK, however, added that when the same will happen, cannot be predicted yet, PTI reported.  

The study also said that antibodies level after complete vaccination with Pfizer is substantially higher than from AstraZeneca shots. It added that the antibodies were also much higher in fully vaccinated people as compared to someone with prior SARS-CoV-2 infection. 

"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. However, we found these levels dropped substantially over the course of two to three months," said Madhumita Shrotri, UCL Institute of Health Informatics, in a statement. 

The study was concluded after 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 said, PTI reported. 

While the clinical implications of waning antibody levels are not yet clear, the researchers said, some decline was expected as current research shows the vaccines are effective against severe COVID disease. 

"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.  

"Even when measurable antibody levels are low, there is likely to be continuing immune memory that could offer long-term protection," the authors of the study noted. 

The researchers, on the basis of the findings, said that critically vulnerable adults or those aged 70 years or over, and all residents of care homes for older adults should be prioritised for booster vaccine shots. 

Further study will be important to establish if there is an antibody level threshold needed for protection against severe disease, the scientists said.