Medical News, Vaccine studies

Vaccine antibody levels shown to significantly decrease after two months

Over 600 people of various ages, genders, and clinical vulnerabilities were studied by the researchers. According to the study, antibody levels decreased from 7506 U/mL to 3320 U/mL for Pfizer, and 1201 U/mL to 190 U/mL for Astrazeneca, after about two months.

Due to the recent rise in COVID-19 cases associated with various SARS-CoV-2 variants, vaccine encouragement is at an all-time high. While July’s data shows Moderna’s COVID-19 vaccine is 76% effective against current COVID-19 infections, Pfizer’s vaccine showed to only be 42% effective.

Pfizer–BioNTech and Oxford–AstraZeneca have substantial immunogenicity and short-term effectiveness, according to current research, but the long-term effects have not been studied in-depth.

The University College at London decided to take a deep dive and measure the long-term effects of the Pfizer and AstraZeneca vaccines. Their results showed that no matter the individuals age or sex, the antibody levels after the second vaccination drastically decrease overtime. 

The researchers performed the study on over 600 individuals all of different ages, genders, and clinical vulnerabilities. They studied the S-anitbody levels for confirmed N-seronegative samples after the second vaccination. They measured their levels periodically and split them in groups from 14-20 days, 21-41, days, 42-55 days, 66-69 days, and 70+ days.

The paper’s results state. “A significant trend of declining S-antibody levels was seen with time for both ChAdOx1 (p<0·001) and BNT162b2 (p<0·001), with levels reducing by about five-fold for ChAdOx1, and by about two-fold for BNT162b2, between 21–41 days and 70 days or more after the second dose. This trend remained consistent when results were stratified by sex, age, and clinical vulnerability.

The study found that the amount of antibodies is greater after the Pfizer vaccine than the AstraZeneca vaccine. Additionally, after about two months, the antibody levels dropped from 7506 U/mL to 3320 U/mL for Pfizer and 1201 U/mL to 190 U/mL for AstraZeneca.

Dr. Maddie Shrotri, a co-author of the UCL paper stated, “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. If they carry on dropping at this rate, we are concerned that the protective effects of the vaccines may also begin to wear off, particularly against new variants; but we cannot yet predict how soon that might happen.” 

The researchers hope that the recently published study helps perpetuate further research into the long-term efficacy of these vaccines, as well as aids policymakers in their decision-making process. The study emphasizes the potential need for booster shots for these vaccines.


The study was published in The Lancet, on July 17th, 2021.

Abstract. Vaccines based on the spike glycoprotein of SARS-CoV-2 are being rolled out globally to control transmission and limit morbidity and mortality due to COVID-19. Current evidence indicates strong immunogenicity and high short-term efficacy for BNT162b2 (Pfizer–BioNTech) and ChAdOx1 nCoV-19 (Oxford–AstraZeneca). Both vaccines are delivered through a prime-boost strategy, and many countries, including the UK, have used dose intervals longer than 3–4 weeks, expecting to maximise first-dose coverage and immunogenicity. With continued high global incidence, and potential for more transmissible SARS-CoV-2 variants, data on longer-term vaccine efficacy and antibody dynamics in infection-naive individuals are essential for clarifying the need for further booster doses.

Shrotri, Madhumita, et al. “Spike-Antibody Waning after Second Dose OF BNT162b2 or ChAdOx1.” The Lancet, vol. 398, no. 10298, 2021, pp. 385–387., doi:10.1016/s0140-6736(21)01642-1. 

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