Previous Covid infection may not offer long-term protection, study finds | Coronavirus

  • June 17, 2021

Previous infection with coronavirus does not necessarily protect against Covid in the longer term, especially when caused by new variants of concern, a study on healthcare workers suggests.

Researchers at Oxford University found marked differences in the immune responses of medical staff who contracted Covid, with some appearing far better equipped than others to combat the disease six months later.

Scientists on the study, conducted with the UK Coronavirus Immunology Consortium, said the findings reinforced the importance of everyone getting vaccinated regardless of whether they had been infected with the virus earlier in the pandemic.

“If you look at the trajectory of the immune response after infection, mostly it is still detectable six months later, but it’s highly variable between people,” said Eleanor Barnes, a professor of hepatology and experimental medicine at Oxford and a senior author on the study.

“That is quite different to vaccination. If you vaccinate you get a really robust response, but with natural infection there’s much more diversity in responses.”

The researchers analysed blood samples from 78 healthcare workers who had Covid, with or without symptoms, between April and June last year. The blood was checked monthly for up to six months post-infection for a range of immune responses. These included different types of antibody that target the virus, B cells that make antibodies and retain a memory of the disease, and T cells, which reduce the severity of disease by killing off infected cells.

Writing in a preprint, which has yet to be peer-reviewed, the authors describe how they used a machine learning system called Simon, for Sequential Iterative Modeling Over Night, to see whether a person’s early immune response and the severity of their infection could predict their longer-term immunity. Dr Adriana Tomic, the first author on the study, said a signature in the antibody and T-cell response at one month predicted how robust the antibody response would be at six months.

The majority of people who produced a weak immune response at one month had no detectable antibodies that could neutralise the Alpha variant, first seen in Kent, at six months. None mounted neutralising antibodies against the Beta variant first spotted in South Africa. The researchers have yet to analyse data for the Delta variant now dominant in the UK.

While most of the healthcare workers who developed symptomatic disease had a measurable immune response six months later, more than a quarter did not. More than 90% of those who had asymptomatic infections had no measurable immune response six months later, the researchers found. The work is part of the protective immunity from T cells to Covid-19 in health workers (Pitch) study, funded by the Department of Health.

“In our view, previous infection does not necessarily protect you long-term from Sars-Cov-2, particularly variants of concern,” said Barnes. “You shouldn’t depend on it to protect you from subsequent disease, you should be vaccinated.”

The wide variability in immunity triggered by natural infection in part reflects the radically different exposures people can have to the virus while going about their lives. Immunity from vaccination is more reliable because people are given a standard dose in a standard way.

Danny Altmann, a professor of immunology at Imperial College London, who was not involved in the study, said the findings cautioned against simple assumptions around how immunity waned with time. “People show rather diverse trajectories after infection, but immunity often seems to hold up well at six months,” he said. “Most of all, studies such as this remind us that policy decisions on ‘boosting’ need to be evidence based in the context of a strong programme of immune monitoring.”

Covid immunity lasts for a year, vaccine boost helps fight variants, study says

Covid immunity lasts for a year, vaccine boost helps fight variants, study says

  • June 16, 2021
Covid-19 vaccine shot | Representational image | Bloomberg


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New Delhi: Immunity in Covid-recovered patients is long-lasting and gets a 50-fold boost after vaccination, according to a new study.

The study, published in the journal Nature Monday, also said that the mRNA vaccines can sufficiently protect against emerging mutations.

More than a year after the Covid-19 pandemic broke, the emergence of new variants that appear to be more transmissible and resistant to antibodies has added to the challenge of controlling the spread of the disease.

To understand how long the immunity lasts, researchers from the Rockefeller University, Weill Cornell Medicine and California Institute of Technology assessed the blood samples of 63 people who had recovered from Covid-19. The samples were collected 1.3, 6.2 and 12 months after infection.

Of these 63 people, 41 per cent had received mRNA vaccines.

The study found that in Covid-recovered patients, antibodies against the protein known as receptor binding domain (RBD) of SARS-CoV-2 and neutralising activity remain relatively stable from six to 12 months, without vaccination.

A receptor-binding domain is a key part of the virus located on its ‘spike’ protein that allows it to latch onto the cell to gain entry into cells and lead to infection.

Memory B cells — a type of white blood cells that learn to recognise specific viral proteins — was also found to remain stable upto 12 months.


Also read: New atomic-scale 3D map of Covid virus protein could hold clue to preventing lung damage


Antibody levels

In addition, the team found that vaccination increases all components of the antibody response. Antibody levels remained relatively unchanged between six to 12 months after SARS-CoV-2 infection, and that vaccination further boosted this activity by nearly 50-fold.

The study found that the ability of vaccine-induced antibodies to neutralise variants of concern was comparable to or greater than that against the original virus.

Researchers also identified that the broad response against the SARS-CoV-2 virus involves what is known as the antibody somatic mutation — a cellular mechanism using which the body’s immune system adapts to the changing virus during the course of the infection.

This results in antibodies that are exceptionally resistant to mutations in the SARS-CoV-2 RBD — including those found in variants of concern

In addition, B cells that produce a broad range of potent antibodies are retained in the body over time and expand dramatically after vaccination.

The data suggest that immunity in Covid-recovered individuals will be very long-lasting, researchers said. Along with this, Covid-recovered patients who receive mRNA vaccines produce antibodies and memory B cells that should be protective against circulating SARS-CoV-2 variants, the study concluded.

(Edited by Neha Mahajan)


Also read: AY.1 — The new Covid variant on world radar stems from Delta variant, linked to immune escape


 

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