Studies have found that SARS-CoV-2 immunity can last for more than 6 months

Currently, more than 56.56 million people worldwide are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is the causative agent of coronavirus disease 2019 (COVID-19) and 1.35 million. More than one person has died. Meanwhile, more than 39.35 million people have recovered from the infection. A problem that currently confuses researchers is the lifespan or duration of immunity to reinfection among recovered people.

US-based scientists from the Lahoya Immunology Institute at the University of California, San Diego and the Mount Sinai Medical College have published a study on preprint servers. bioRxiv *, “Immunological memory for SARS-CoV-2 evaluated for more than 6 months after infection, ”Contributes to the enormous research efforts currently underway in this area.

Background

Understand, as researchers point out Effectiveness of For vaccines currently under development, it is important to know the lifespan of immunological memory for SARS-CoV-2. They also added that this would help develop better diagnostic methods for infectious diseases.

Overall, the ability to quantify individual immune responses to SARS-CoV-2 infections and define their lifespan can more accurately predict the future course of pandemics.

antibody

Viral infections are known to release SARS-CoV-2 specific antibodies and stimulate CD4 + T cells and CD8 + T cells. “CD4 + T-cell and CD8 + T-cell response may be important in controlling and resolving primary SARS-CoV-2 infections,” because this T-cell response leads to less severe disease, “the researchers said. Are writing.

The· Neutralizing antibody Protection against infection can be protected from secondary infection by SARS-CoV-2. When these neutralizing antibodies are given passively – Convalescent plasma For example, the severity of blood transfusion-infection was found to be less severe in laboratory animals. However, in humans, if this passive transfer of neutralizing antibody provided after the infection has already begun has failed to significantly control the severity of the infection. This means that T cells in infected individuals play an important role in protection from secondary infections, not just antibodies, the researchers write.

Circulating memory T cells and memory B cells can take several days to reactivate when re-infected, and this reactivation can trigger a “recall T cell response and / or prior antibody response.” there is.

“The development of the COVID-19 vaccine is closely related to the topic of immunological memory.” This study found that “three branches of adaptive immunity (CD4 + T cells, CD8 + T cells, and humoral immunity). ) ”Was done to assess immune memory, they add.

Study design

This study analyzed immune memory for SARS-CoV-2 in 185 COVID-19 cases who recovered over 6 months after recovery from infection. Forty-three percent of the participants were men and 57% were women. Participants suffered from a wide range of severe illnesses, from asymptomatic to severe. They have been hired from multiple sites. Of the patients, 7% needed hospitalization and some needed intensive care room (ICU) care.

Diseases from 0 to 10 were scored using the NIH ordinal scale numerical scoring system, including adults with confirmed infections. The team scored 1 for “asymptomatic” cases, 2 or 3 for “mild symptoms”, 4 or 5 for “moderate symptoms or disorders”, and “severe disorders”. The score of the case is explained as a score. 6 years and over. Those with a score above 4 needed to be hospitalized.

Blood samples were collected for antibody analysis and SARS-CoV-2 specific CD4.⁺ T cells and CD8⁺ T cell assay and memory B cell assay. Spike receptor binding domain (RBD) IgG was also measured. SARS-CoV-2 specific memory B cells were identified using a fluorescently labeled multimerization probe.

Most of the participants provided blood samples 6 days after the onset of symptoms and then 240 days after the onset of symptoms. A total of 41 samples were obtained more than 6 months (178 days or more) after the onset of symptoms. A total of 38 participants provided samples with 2-4 points during the study period.

Survey results

Overall, the study results showed that the specific antibody response of the virus to the spike protein (called spike IgG) was stable in convalescent patients for more than 6 months. Spike protein-specific memory B cells were also abundant at 6 months. The number of these memory B cells was found to be higher at 6 months after infection than at 1 month after recovery. SARS-CoV-2 specific CD4⁺ T cells and CD8⁺ The half-life of T cells was 3 to 5 months, after which it showed a decreasing trend.

Antibody level:

• One month (20 to 50 days) after the onset of symptoms, 98% were serum positive for spike IgG.
• 90% were seropositive for spiked IgG at 6-8 months (after 178 days of onset of symptoms)
• SARS-CoV-2 RBD IgG titer had a half-life of 83 days
• 88% were serum positive for RBD IgG in 6-8 months (after 178 days of onset of symptoms)
• Six to eight months after the onset of symptoms, 90% of subjects were serum-positive for SARS-CoV-2 neutralizing antibody (titer> 20).
• The half-life of circulating RBDIgA was 27 days

Memory B cells:

Spike-specific memory B cells in SARS-CoV-2 unexposed donors were rare. Spike-specific memory B cells increased from the first measurement on days 36-163 to the second measurement from days 111-240. The author writes: Robust and probably long lasting. “

Memory T cell:

SARS-CoV-2 memory CD8 + T cells were identified in 155 subjects. SARS-CoV2 memory CD8 + T cells were found in 61% of participants 20-50 days after onset of symptoms. Six months after the onset of symptoms, the proportion of subjects with SARS-CoV-2 memory CD8 + T cells was 50%.

According to the researchers, the response of SARS-CoV-2 memory CD4 + T cells was strong. Twenty to fifty days after the onset of symptoms, SARS-CoV2 memory CD4 + T cells were found in 94% of participants. Six months after the onset of symptoms, 89% of subjects had SARS-CoV-2 memory CD4 + T cells.

Conclusions and implications

The authors of the study concluded that each component of SARS-CoV-2 immune memory, including antibodies, memory B cells, and CD4.⁺ T cells and CD8⁺ T cell memory for SARS-CoV-2 showed a strong presence months after recovery from infection. They write: “Immune memory, consisting of at least three immune compartments, is measurable in approximately 90% of PSO (post-symptom onset) subjects over 5 months and indicates persistent immunity to 2.^O (Secondary) COVID-19 disease is a disease that can occur in most people. “

*Important Notices

bioRxiv publishes unread preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.