According to a study published in The Lancet journal, total antibody levels begin to decline. After six weeks post, complete immunization with Pfizer and AstraZeneca vaccines the antibodies can drop by more than 50% in ten weeks.
According to experts from University College London (UCL) in the United Kingdom, if antibody levels continue to drop at this rate, the vaccinations’ protective benefits may begin to wear off, especially against novel variants.
However, they stated that the timing of this event cannot be predicted at this time.
The UCL Virus Watch research also revealed that after two doses of the Pfizer vaccination, antibody levels are significantly higher than after two shots of the AstraZeneca preventive. Astra Zeneca in India is known as Covishield.
Antibody levels were also much higher in vaccinated people than in people who had previously been affected with SARS-CoV-2, according to the researchers.
“Antibody levels following both doses of either the AstraZeneca or Pfizer vaccine were initially quite high, which is likely to be an important part of why they are so protective against severe COVID-19,” said Madhumita Shrotri of the University College London Institute of Health Informatics.
“However, over two to three months, we found these levels had dropped substantially,” Shrotri said in a statement. According to the researchers, the findings based on data from over 600 persons aged 18 and up were consistent across all groups of people regardless of age, chronic conditions, or sex.
Although the clinical implications of declining antibody levels are not yet clear, the authors point out that some reduction had to be expected. Recent research suggests that immunizations are still effective against severe disease.
Antibody levels dropped from 7506 Units per milliliter (U/mL) at 2141 days to 3320 U/mL after 70 days or more for Pfizer. Antibody levels for the AstraZeneca vaccine dropped from a median of 1201 U/mL at 020 days to 190 U/mL at 70 or more days, a five-fold decline.
“Our data implies that those who were vaccinated first, particularly with the AstraZeneca vaccine, are likely to have the lowest antibody levels presently,” said Professor Rob Aldridge of the University College London Institute of Health Informatics.
The findings back up recommendations that clinically vulnerable persons, those aged 70 or older, and all residents of nursing homes for the elderly be given booster doses first, according to the researchers.
The researchers emphasized that because each person only provided one sample. They can’t yet say how quickly antibody levels drop for each person, or whether they’ll continue to drop or stabilize in the upcoming months.
They also pointed out that different people will have varying levels of immunity based on their antibodies’ ability to neutralize viruses as well as their T-cell responses.
“Even when measured antibody levels are low, there is likely to be ongoing immune memory that can provide long-term protection,” the study’s authors wrote.
