In the ongoing debate of how long those who have recovered from a COVID-19 infection could have immunity against the novel coronavirus, a new study — which is said to be the most comprehensive to date — offers an encouraging answer.
In a study published to the pre-preprint server bioRxiv on Monday, researchers said that immunity against SARS-CoV-2, the virus that causes a COVID-19 infection, could last for at least six months, or it could be longer, perhaps a matter of years.
The study, which has not yet been peer reviewed or published in a scientific journal, was conducted by scientists at the La Jolla Institute of Immunology in California and the Icahn School of Medicine at Mount Sinai in New York.
Researchers analyzed various aspects of immunity, including antibodies, B cells and two types of T cells. T cells respond to a foreign invader such as a virus but are different from antibodies and are thought to provide immunity against the coronavirus for a longer period of time.
The study involved 185 U.S. adults ages 19 to 81. All had contracted the virus but had recovered, with most suffering only mild illness. Researchers collected blood samples from the study participants, with some participants giving only one sample while others gave samples over a series of months, according to the study.
By the end, the researchers noted that antibodies were “durable,” showing only modest declines after six to eight months. The antibody responses among the participants “spanned a 200-fold range,” the researchers said in the study.
T-cell memory, meanwhile, “might reach a more stable plateau, or slower decay phase, later than the first 6 months post-infection," they wrote, while B cells grew in number and “were more abundant at 6 months than at 1 month,” they said.
The findings bolster past research on coronavirus immunity, including one study that showed immunity in recovered COVID-19 patients for at least three months. Additionally, the researchers noted, the findings are “also consistent with [the] recent detection of SARS-CoV T cells 17 years after the initial infection.” In other words, the findings are in line with a recent discovery that survivors of the SARS outbreak in the early 2000s still had T cells against that coronavirus more than a decade after recovering.
“That amount of memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years,” Shane Crotty, a virologist at the La Jolla Institute of Immunology who co-led the study, told The New York Times of the findings.
The findings also sparked reactions from scientists who were not a part of the study.
“This preprint has yet to be peer-reviewed but brings exciting news. The immune system is more than just antibodies in the blood and these authors have carefully measured different types of antibodies and different types of immune memory cells to see how long immunity lasts. They identify particular types of memory B cells and memory T cells which are still present in good quantities six to eight months after infection,” said Deborah Dunn-Walters, a professor of immunology at University of Surrey and chair of the British Society for Immunology expert advisory group on COVID-19 Immunology, in a statement distributed by the United Kingdom's Science Media Centre.
“In fact, the cells continued increasing for two or three months after symptom onset. So even if the levels of antibody in the blood go down, there are cells standing by ready to make new ones if needed,” she continued.
“The paper confirms the importance of looking at memory B cells and memory T cells in order to assess immunity and shows the best types of memory cells to look for and the best time to look for them. It gives us hope that immunity to SARS-CoV-2 could last for several years,” added Dunn-Walters.