Contrary to current belief that recovered Covid-19 patients have antibodies to fight the disease for up to three to five months, a significant study has claimed that the protective immunity against the SARS-CoV-2 virus could last for at least eight months or more. The fact that immune memory against SARS-CoV-2 is possible for more time is also a good sign for vaccine developers.
The findings published in the prestigious journal Science helps clarify some Covid-19 concerning data from other labs, which showed a dramatic drop-off of Covid-fighting antibodies in months following the infection.
Some feared that this decline in antibodies meant that the body wouldn't be equipped to defend itself against re-infection.
"Our data suggests that the immune response is there -- and it stays," said researcher Alessandro Sette, a professor at La Jolla Institute for Immunology in the US.
According to the researchers, nearly all Covid-19 survivors have the immune cells necessary to fight re-infection.
For the study, the research team analysed blood samples from 188 Covid-19 recovered patients.
"We measured antibodies, memory B cells, helper T cells and killer T cells, all at the same time," said Shane Crotty, a professor at the Institute.
"As far as we know this is the largest study ever for any acute infection that has measured all four of those components of immune memory," Crotty added.
The findings suggested that responses to the novel coronavirus, SARS-CoV-2, from all major players in the "adaptive" immune system, which learns to fight specific pathogens, could last for at least eight months after the onset of symptoms from the initial infection.
Study co-author Daniela Weiskopf emphasised that the study tracked responses to natural SARS-CoV-2 infection, not immune memory after vaccination.
"It is possible that immune memory would be similarly long lasting following vaccination, but we will have to wait until the data comes in to be able to tell for sure," Weiskopf said.
"The vaccine studies are at the initial stages and so far have been associated with strong protection. We are hopeful that a similar pattern of responses lasting over time will also emerge for the vaccine-induced responses".
The researchers said they would continue to analyse samples from Covid-19 patients in the coming months and hope to track their responses 12 to 18 months after the onset of symptoms.
"We are also doing very detailed analyses at a much, much higher granularity on what pieces of the virus are recognised," said Sette.
The researchers found that virus-specific antibodies do persist in the bloodstream months after infection. Importantly, the body also has immune cells called memory B cells at the ready.
If a person encounters SARS-CoV-2 again, these memory B cells could reactivate and produce SARS-CoV-2 antibodies to fight re-infection.
The SARS-CoV-2 virus uses its "spike" protein to initiate infection of human cells, so the researchers looked for memory B cells specific for the SARS-CoV-2 spike. They found that spike-specific memory B cells actually increased in the blood six months after infection.
Sette explains that a decline in antibodies is very normal.
"Of course, the immune response decreases over time to a certain extent, but that's normal. 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," the researcher opined.