Second COVID-19 booster substantially raises immunity, trial shows

People who already have high antibody titres, such as from infection, do not benefit as much, say researchers

Boosting with a fourth dose of mRNA vaccine can substantially increase immunity against COVID-19, in some cases beyond the peak response achieved after a third dose, according to a first-of-its-kind trial.  


However, researchers say the benefits of a fourth dose appear limited for people whose immune response has remained elevated because of recent infection or vaccination, indicating there might be a ‘ceiling effect’. 

The UK Government-funded COV-Boost substudy, conducted at 18 sites, is the