Immune system 'remembers' coronavirus for at least six months

People may be able to fight off reinfection for at least six months after they recover from Covid-19 thanks to cells that can “remember” the virus, according to research published yesterday.

Researchers in the United States and Switzerland studied dozens of people who had recovered from Covid-19 and found that while their antibodies may fade over time, they maintained levels of specific memory B cells.

These cells can remember the pathogen and can, if faced with reinfection, prompt the immune system to reinitiate the production of virus-fighting antibodies.

“Memory responses are responsible for protection from reinfection and are essential for effective vaccination,” concluded the study published in the journal Nature.

“The observation that memory B cell responses do not decay after 6.2 months, but instead continue to evolve, is strongly suggestive that individuals who are infected with SARS-CoV-2 could mount a rapid and effective response to the virus upon re-exposure.”

The authors assessed 87 people with a confirmed Covid-19 diagnosis at a little over one month and six months after infection.

While they found that virus neutralising antibody activity decreased with time, the number of memory B cells remained unchanged.

Researchers said their study indicated that the memory B cell response against the coronavirus evolves during the six months after infection in the presence of viral remnant proteins in the body -- enabling the cells to produce more potent antibodies.

How long people can fight off reinfection to the new coronavirus and what immune process is involved are key to predicting the dynamics of the pandemic.

Previous research has caused concern by showing that neutralising antibodies can decline quickly after infection with SARS-CoV-2.

But more recent studies have highlighted the role of other parts of the immune system in longer-term immunity.   

One paper published in the journal Science this month suggested that nearly all major parts of the immune system that can learn to recognise and repel a new pathogen could continue to respond to the virus for at least eight months.

This included protein spike specific memory B cells, which the researchers found actually increased in the blood six months after infection.

The paper was based on analyses of blood samples from 188 Covid-19 patients.

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Gene-editing may produce dangerous unintended mutated viruses

Using gene-editing tools to create virus-resistant plants may have an unintended consequence of propagating of mutated viruses, according to scientists.

Researchers  attempted to genetically engineer cassava plants to fight off viruses. 

"Because this technology creates a selection pressure on the viruses to evolve more quickly, and also provides the viruses a means to evolve, it resulted in a virus mutant that is resistant to our interventions," said a researcher.

For the study, the researchers used a new gene-editing technology called CRISPR-Cas9 in an attempt to design cassava plants that could cut the DNA of the mosaic virus and make the plants resistant to its damaging effects. 

They were not successful and decided to sequence hundreds of viral genomes found in each plant to understand exactly what happened.

"We discovered that the pressure that CRISPR-Cas9 applied to the virus probably encouraged it to evolve in a way that increased resistance to intervention," said the researcher, who noted CRISPR-Cas9 has many other applications in food and agriculture that do not pose the same risks.

CRISPR-Cas9 is found in nature, where bacteria use it to defend against viruses. However, the researchers found the technology results in different outcomes in plants -- and researchers are stressing the importance of screening against these sorts of unintended results in the future.

The cassava plant is a starchy root vegetable that is consumed for food throughout the tropics. 

Cassava is a primary staple crop grown in South America, Africa and Asia, from which a billion people get most of their calories each day. Each year, cassava crops are plagued by cassava mosaic disease, which causes 20 per cent crop loss. 

It is the mosaic disease that researchers endeavoured to engineer against.

The research team is encouraging other scientists who are using CRISPR-Cas9 technology to engineer virus-resistant plants, to test their plants to detect similar viral mutations.

"We need to do more research on these types of applications of CRISPR-Cas9 technology before we proceed with field testing," said the researcher.

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