One Kind of Immunity to the Coronavirus Lasts at Least Six Months, Study Finds

One Kind of Immunity to the Coronavirus Lasts at Least Six Months, Study Finds
Blood samples about to be tested for covid-19 antibodies at a clinic in Moscow on May 15, 2020 (Photo: Vasily Maximov, Getty Images)

New research this week offers some hope for at least one aspect of our immunity to the coronavirus that causes covid-19. The study, conducted by researchers in the UK, found evidence that certain T cells created to combat the coronavirus during infection continue to show a “robust” response at least six months later. This cellular immune response is thought to play an important role in preventing reinfection or lessening the severity of a subsequent infection, alongside other components of our immunity like antibodies.

The new research is the work of the UK Coronavirus Immunology Consortium, a nationwide study backed by the UK government and involving several universities. As part of the project, the researchers have kept track of 100 volunteers who all tested positive for antibodies to the coronavirus sometime in March or April. Though some people developed symptoms at the time of their diagnosis, none needed hospitalisation.

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T cells are one of the main cells of the immune system. They carry out a wide assortment of duties during an infection, from directly trying to kill infected cells to helping other cells do their job better, including those that produce the proteins we call antibodies. Like antibodies, our body can produce T cells that specifically “remember” a past pathogen and are able to leap in action when it tries to reinfect us. Compared to studying how antibodies respond to a germ, though, a person’s cellular immune response is more complex and harder to measure. That makes this study one of the most important and largest of its kind.

The early results, released in a paper on the preprint website bioRxiv on Tuesday, certainly look encouraging. All of the volunteers appeared to develop T cells specific to the virus soon after diagnosis, the researchers found. And when the volunteers’ blood was studied six months later, these T cells seemed to remain in their system.

“To our knowledge, our study is the first in the world to show robust cellular immunity remains at six months after infection in individuals who experienced either mild/moderate or asymptomatic,” said Paul Moss, a hematologist at the University of Birmingham and one of the project’s lead scientists, in a statement released by the Consortium Tuesday.

Immunity to a disease like covid-19, as we have discussed before, is a complicated mess. Some research has suggested that coronavirus-specific antibodies can fade away in as little as three months, yet other research has suggested that the most important antibodies — those that directly prevent the virus from infecting new cells — can be sustained in most survivors for at least five months. And there are still other parts of the immune system relevant to covid-19 that haven’t been studied in much detail, such as memory B cells.

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Experts do expect our natural immunity to the coronavirus to start waning eventually, simply based on our history with other coronaviruses that make us sick (how vaccine-induced immunity will work is still uncertain). But the findings from this new study and others suggest that some level of protection should endure for more than a few months. This protection may not necessarily prevent reinfection in all cases (indeed, we are starting to see scattered cases of reinfection reported throughout the world), but it will likely blunt the impact of a second infection if it does happen, experts have told Gizmodo.

There’s still a lot about our immune response to covid-19 left to be understood, and the findings from this study will provide new breadcrumbs for scientists to follow.

For instance, the study found that people who felt sick tended to have a stronger T-cell response than those who were asymptomatic, which could suggest that symptomatic survivors are better protected. People’s level of T-cell response over time also strongly correlated to their level of antibodies to the virus, while a larger T-cell response at the start was linked to a slower decline of antibodies. That likely means that any future vaccines will have to provoke a strong T-cell response in addition to an antibody response in order to be effective as possible.