Study shows immune cells against COVID-19 stay high in number six months after vaccination

A recent study by Johns Hopkins Medicine researchers provides evidence that CD4+ T lymphocytes — immune system cells also known as helper T cells — produced by people who received either of the two available messenger RNA (mRNA) vaccines for COVID-19 persist six months after vaccination at only slightly reduced levels from two weeks after vaccination and are at significantly higher levels than for those who are unvaccinated. The researchers also found that the T cells they studied recognize and help protect against the delta variant of SARS-CoV-2, the virus that causes COVID-19. According to the U.S. Centers for Disease Control and Prevention, the delta variant — currently the predominant strain of SARS-CoV-2 in the United States — causes more infections and spreads faster than earlier forms of the virus. The study findings were first reported online Oct. 25, 2021, in the journal Clinical Infectious Diseases. “Previous research has suggested that humoral...