Protective immunity against coronavirus may last for over eight months
(Sourced from PTI)
COVID-19 survivors may have protective immunity against the fatal disease caused by the SARS-CoV-2 virus for months or even years after the infection, a study published in the journal Science suggests. The findings, based on the analysis of blood samples from 188 COVID-19 patients, suggest that nearly all survivors of the disease have the immune cells necessary to fight re-infection.
"Our data suggest that the immune response is there -- and it stays," Professor Alessandro Sette from La Jolla Institute for Immunology in the US said. The study helps clarify some concerning data, which showed a dramatic drop-off of COVID-19 fighting antibodies in the months following infection. Some feared that this decline meant that the body wouldn't be equipped to defend itself against re-infection.
Sette explained that a decline in antibodies is rather normal. "Of course, the immune response decreases over time to a certain extent, but that's normal," he noted. "That's what immune responses do. They have a first phase of ramping up, and after that fantastic expansion, eventually, the immune response contracts somewhat and gets to a steady state," Sette added.
The researchers measured antibodies, memory B cells, helper T cells, and killer T cells, all four components of immune memory, and found that virus-specific antibodies persist in the bloodstream months after infection. They said the body also has immune cells (memory B cells) readily available, adding that if a person encounters SARS-CoV-2 again, these cells could reactivate and produce antibodies to fight re-infection.
The SARS-CoV-2 virus uses its "spike" protein to initiate infection of human cells. The researchers looked for memory B cells specific for the SARS-CoV-2 spike and found that those cells increased in the blood six months after infection. "COVID-19 survivors also had an army of T cells ready to fight re-infection," the researchers further added.
"The different parts of the adaptive immune systems work together, so seeing COVID-19-fighting antibodies, memory B cells, memory CD4+ T cells and memory CD8+ T cells in the blood more than eight months following infection is a good sign," said LJI Professor Shane Crotty.
However, the researchers cautioned that protective immunity does vary dramatically from person to person. They saw a 100-fold range in the magnitude of immune memory. "People with a weak immune memory may be vulnerable to a case of recurrent COVID-19 in the future, or they may be more likely to infect others," the researchers said.