Israeli trial shows a fourth vaccination raises antibody levels but provides little extra protection against SARS-CoV-2 infection.
could be beneficial for people at higher risk of severe illness. Several countries, including Israel, Chile and Sweden, are offering fourth doses to older adults and other groups.
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 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%.That meant that, by the end of January, 52 participants who had received a fourth dose had tested positive for SARS-CoV-2 and 73 of the matched controls who had received only three doses had done so.