Oxford University Study: The dynamics of immunity following second doses differed significantly between BNT162b2 (Pfizer) and ChAdOx1 (AZ), with greater initial effectiveness .. but faster declines in protection against high viral burden and symptomatic infection with BNT162b2. There was no evidence that effectiveness varied by dosing interval, but protection was higher among those vaccinated following a prior infection and younger adults. With Delta, infections occurring following two vaccinations had similar peak viral burden to those in unvaccinated individuals.

So both decline - Pfizer nRMA declines fastest.

Vaxxed people contracting Delta experience the same 'viral burden' as unvaxxed.

Israel and US are already giving booster shots for Pfizer. That indicates it's running out of puff after about 4-6mths.

Meanwhile Pfizer has pumped up its price. One thing i will say for AZ is that it's not a profit-gouging outfit like Pfizer.

Interesting to see Oxford hitting back in the data war after Pfizer had secured PR supremacy.