Covid19 – Study shows AstraZeneca and Pfizer vaccine antibody levels may decline post 2-3 months
Total antibody levels start to wane six weeks after complete immunisation with Pfizer and AstraZeneca vaccines, and can reduce by more than 50 per cent over 10 weeks, according to study published in The Lancet journal. 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.
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. “However, we found these levels dropped substantially over the course of two to three months,” Shrotri said in a statement.
For Pfizer, antibody levels reduced from a median of 7506 Units per millilitre (U/mL) at 21–41 days, to 3320 U/mL at 70 or more days.
For AstraZeneca vaccine, antibody levels reduced from a median of 1201 U/mL at 0–20 days to 190 U/mL at 70 or more days, over five-fold reduction.
The researchers noted that that each individual only contributed one sample, so they cannot yet confirm how quickly antibody levels drop for each individual, or whether these would continue to drop or reach a stable level over the next few months. They also noted that different people will have different levels of immunity depending on the virus neutralising ability of their antibodies as well as their T-cell responses.
The findings support the recommendation that clinically vulnerable adults, adults over the age of 70, and all residents of elderly care facilities should prioritize booster immunization, the researchers said. Said. In addition, those who received the AstraZeneca vaccine are likely to have much lower antibody levels than those who received the Pfizer vaccine, they said.
“Even with low measurable antibody levels, immunological memory that can provide long-term protection is likely to continue,” the study authors said. They said further research was important to establish whether there was a threshold for the required antibody levels. For protection from severe illness.
Mixed vaccination of first AstraZeneca and then a Pfizer Covid-19 shot boosted neutralizing antibody levels by six times compared with two AstraZeneca doses, a study from South Korea showed.
The study involved 499 medical workers – 100 receiving mixed doses, 200 taking two doses of the Pfizer/BioNTech shot and the remainder getting two AstraZeneca shots. All showed neutralizing antibodies, which prevent the virus from entering cells and replicating, and the result of the mixed schedule of vaccines showed similar amounts of neutralizing antibodies found from the group that received two Pfizer shots.
A British study last month showed similar results that an AstraZeneca shot followed by Pfizer produced the best T-cell responses, and a higher antibody response than Pfizer followed by AstraZeneca.
Antibodies triggered by Sinovac COVID-19 vaccine declined below a key threshold from around six months after a second dose for most recipients, although a third shot had a strong booster effect, according to a lab study. Chinese researchers reported the findings from a study of blood samples from healthy adults aged between 18-59 in a paper published on Sunday, which has not been peer reviewed.
Researchers said it was unclear how the decrease in antibodies would affect the shot’s effectiveness, since scientists have yet to figure out precisely the threshold of antibody levels for a vaccine to be able to prevent the disease.