SARS-CoV-2 anti-spike IgG antibody responses after second dose of ChAdOx1 or BNT162b2 in the UK general population

We investigated anti-spike IgG antibody responses following second doses of ChAdOx1 or BNT162b2 SARS-CoV-2 vaccines in the UK general population. In 186,527 individuals, we found significant boosting of anti-spike IgG by second doses of both vaccines in all ages and using different dosing intervals, including the 3-week interval for BNT162b2. After second vaccination, BNT162b2 generated higher peak levels than ChAdOX1. Antibody levels declined faster at older ages than younger ages with BNT162b2, but were similar across ages with ChAdOX1. With both vaccines, prior infection significantly increased antibody peak level and half-life. Protection was estimated to last for 0.5-1 year after ChAdOx1 and >1 year after BNT162b2, but could be reduced against emerging variants. Reducing the dosing interval to 8 weeks for both vaccines or further to 3 weeks for BNT162b2 may help increase short-term protection against the Delta variant. A third booster dose may be needed, prioritised to more vulnerable people.