Spike-antibody waning after second dose of BNT162b2 or ChAdOx1 - The Lancet
▻https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01642-1/abstract
(#Vaccins Pfizer et AZ)
A significant trend of declining S-antibody levels was seen with time for both ChAdOx1 (p<0·001) and BNT162b2 (p<0·001; figure; appendix), 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 [..,]
[…]
Across both vaccine types, women had higher initial S-antibody levels than men at 21–42 days after complete vaccination; also ending with higher levels at 70 days or more (appendix). Similarly, those aged 18–64 years had higher levels at 21–42 days compared to those aged 65 years and older, with correspondingly higher levels at 70 or more days (appendix).
[…]
This analysis should be repeated with a larger number of participants to allow better adjustment for potential confounding, and with longitudinal follow-up of antibody dynamics in individuals over 6–12 months to establish plateau levels, or time to seroreversion.
Higher antibody levels are possibly associated with greater protection against variants that can partially evade immunity, which could explain the observed higher efficacy (partly preliminary) of BNT162b2 compared to ChAdOx1 against the Delta variant (B.1.617.2). Disparity in peak antibody levels between vaccine types, and to a lesser extent between population groups, might therefore be important if antibody levels in some groups drop below ( as yet undefined) thresholds of protection earlier than in others.
There is, however, accumulating evidence suggesting the importance of T-cell-mediated immunity, particularly in individuals with weak or absent antibody responses, so it is possible that T-cell responses compensate to some extent as antibody responses wane.
In the context of recent advice in support of booster vaccinations from the UK’s Joint Committee on Vaccination and Immunisation, and given the potentially rapid S-antibody decline suggested by these data, heterologous regimens, which preliminary data suggest elicit stronger antibody and T-cell responses,, might provide more durable immunity and greater protection against emerging variants.
However, the ultimate effect of different dose intervals and various heterologous combinations on clinical outcomes remain important unanswered questions . Principally, the ethical basis for universal booster dose deployment in high-income settings should be carefully considered in the context of widening global vaccine inequities. Data on disparities in peak antibody levels and rates of decline might therefore inform targeted and equitable booster deployment.