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Covid immunity in recovered patients could last up to 8 months, says study

Scientists at an institute in the US found that nearly all 188 Covid cases studied had immune memory at five to eight months after symptom onset.

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New Delhi: Recovered Covid-19 patients have immunity from the novel coronavirus for up to eight months, a new study has found.

The study, published in journal Science Wednesday, was conducted using samples from 188 Covid cases across the US, at the La Jolla Institute of Immunology.

“If we had seen only marginal immune responses, we would have been concerned,” Alessandro Sette, professor, Center for Infectious Disease and Vaccine Research, said in a statement.

“…but what we see is a very robust T cell response against the spike protein, which is the target of most ongoing COVID-19 efforts, as well as other viral proteins. These findings are really good news for vaccine development,” Sette added.  

While the duration of immune response to the virus has been studied throughout the pandemic, a study by King’s College London had worryingly found that antibody levels that can destroy the virus peaked about three weeks after the onset of symptoms.

However, cases of reinfection remain rare across the world.


Also read: India will be able to vaccinate entire population soon, says Harsh Vardhan


Methodology

The latest study was conducted on 254 samples from 188 Covid cases. The subjects included 80 males and 108 females, aged between 19 and 81 years, and represented a range of asymptomatic, mild, moderate, and severe Covid cases.

However, most subjects had mild Covid cases with 93 per cent never requiring hospitalisation. The rest included those who required ICU care. Ninety seven per cent of the subjects, however, were symptomatic.

Samples were collected from the subjects between 6 days and 240 days post symptom onset (PSO), with 43 samples which were at over six months after infection.

Immunity memory

The study focused on the following five immune memory responses: RBD IgG, RBD memory B cells, Spike IgA, total SARS-CoV-2-specific CD8+T cells, and total SARS-CoV-2-specific CD4+ T cells. These are types of white blood cells which help in immune responses.

Over every three out of five Covid cases were positive for all five of these immune memory compartments at one to two months PSO.

At five to eight months PSO, the proportion of individuals positive for all five of these immune memory compartments had dropped to 43 per cent; but 95 per cent of individuals were still positive for at least three out of five immune memory responses.

Immune memory at five to eight months PSO represented contributions from different immune memory compartments in different individuals.

“Our data show immune memory in at least three immunological compartments was measurable in 95% of subjects 5 to 8 months PSO, indicating that durable immunity against secondary COVID-19 disease is a possibility in most individuals,” the study said.


Also read: IMA ‘welcomes’ Covid-19 vaccines, encourages doctors across India to get vaccinated


 

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