Fourth dose of COVID vaccine offers only slight boost against Omicron infection
▻https://www.nature.com/articles/d41586-022-00486-9
Regardless of the vaccine brand, the fourth dose raised participants’ levels of ‘neutralizing’ antibodies, which can block viral infection of cells. But levels after the fourth dose did not surpass those observed shortly after the third dose, suggesting that the vaccines had hit an upper limit. “You can’t keep boosting antibody responses forever,” says Davenport.
The researchers also assessed the neutralizing antibodies from 25 participants for the antibodies’ power against several SARS-CoV-2 variants. They found that, after the third vaccine dose, participants’ antibodies could block Omicron from infecting cells — but not as well as they blocked the Delta variant. After the fourth dose, the antibodies’ potency against Omicron rose but also not more than their potency against Delta.
Those antibody data might explain why the fourth dose did not translate into substantial extra protection against infection with Omicron. A four-dose course of the #Pfizer vaccine was 30% more protective against infection than a three-dose course; for #Moderna, that extra efficacy was 11%.