This was noted in people infected by the first SARS virus, SARS-CoV-1, in 2003. SARS patients who subsequently died had higher antibody levels during acute infection and worse clinical lung injury compared to SARS patients who went on to recover. In MERS, which is also a coronavirus infection, survivors with higher antibody levels experienced longer intensive care unit stays and required more ventilator support, compared to subjects with no detectable antibodies.
In contrast, strong T-cell levels in SARS and MERS patients correlated with better outcomes. The same has also played out, so far, in COVID-19 patients.
“A strong antibody response correlates with more severe clinical disease in COVID-19, while a strong T-cell response is correlated with less severe disease. And antibodies have been short-lived, compared to virus-reactive T-cells in recovered SARS patients,†Hellerstein said.
The most worrisome part, he said, is that antibodies also can make subsequent infections worse, creating so-called antibody-dependent enhancement. Two vaccines — one against a coronavirus in cats and another against dengue, a flavivirus that affects humans — had to be withdrawn because the antibodies they induced caused potentially fatal reactions. If an antibody binds weakly against these viruses or falls to low levels, it can fail to “neutralize†the virus, but instead help it get into cells.