The FLARE Four
- Researchers in China completed serological assessments of 14 patients who had been hospitalized for COVID-19 and became virus-free
- Not only were SARS-CoV-2-specific antibodies detected, but in most patients the antibodies were neutralizing—capable of protecting against re-infection
- There was also evidence of a virus-specific T cell response
- There was strong correlation between neutralization antibody titers and the number of virus-specific T cells, suggesting an integrated humoral and cellular immune response
- While more research is needed, these findings are additional assurance that natural infection confers protective immunity and that future vaccination may be effective
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Studies of SARS-CoV, MERS-CoV and non-SARS coronaviruses, as well as a non–peer-reviewed, pre-print study of rhesus monkeys, suggest humans should possess protective immunity to SARS-CoV-2 after infection. This research was discussed in a fast literature update posted on April 24, 2020.
The newest study of protective immunity in patients recovering from COVID-19, published in Immunity, is the most comprehensive yet. Its promising results are discussed by Tiara Calhoun, MD, Internal Medicine and Global Medicine resident, and Vladimir Vinarsky, MD, a physician in the Division of Pulmonary and Critical Care, with advisory review by Rod Rahimi, MD, PhD, all of Massachusetts General Hospital, in a fast literature update posted on May 5.
Participants and Methods
The researchers evaluated blood samples from eight patients being discharged from a university hospital in Beijing. They also examined blood samples obtained two weeks after discharge from a separate group of six patients. All patients had a positive SARS-CoV-2 nucleic acid test and radiographic signs of mild COVID-19.
Blood from all 14 patients showed IgM and IgG antibodies specific to two proteins derived from SARS-CoV-2: the viral nucleocapsid protein (NP) and the receptor-binding domain of the spike protein (S-RBD). These antibodies were not detected in healthy controls.
Humoral Immune Response
For S-RBD, although not NP, there was a strong correlation between antibody titer and neutralizing activity against SARS-CoV-2.
Cellular Immune Response
The number of T cells secreting interferon-gamma was higher in recovered COVID-19 patients than in controls, suggesting a SARS-CoV-2-specific T cell response. There was also a strong correlation between neutralization antibody titers and the number of virus-specific T cells.
- Similar to all prior COVID-19 immunology studies, a very small number of patients were evaluated
- No information is given about changes in immunity over time in the same patients
- It remains unknown what antibody titer or number of memory T cells is needed to confer protection
This study provides encouraging, but certainly not definitive, evidence that humans develop protective immunity after COVID-19.
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Learn more about immunology research at Mass General