Hybrid immunity was preserved for 6 months after SARS-CoV-2 exposure

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to the 2019 coronavirus disease (COVID-19) pandemic. Several SARS-CoV-2 variants have emerged since the beginning of the pandemic, and compared with ancestral variants, the rate of infection, virulence, and differ in their ability to evade immune responses.

study: Hybrid immunity 6 months after SARS-CoV-2 exposure in individuals in community treatment programs. Image Credit: Cinefootage Visuals / Shutterstock.com

Background

The SARS-CoV-2 Delta variant was the predominant circulating strain in Thailand by mid-August 2021. The spread of this variant has significantly increased the number of COVID-19 cases and deaths.

During this period, the number of daily cases reached approximately 20,000 and more than 300 deaths were reported daily. His subsequent decline in COVID-19 cases followed the implementation of pharmaceutical and non-pharmaceutical measures.

Previous studies have shown that COVID-19 vaccination plays an important role in reducing hospitalizations due to daily infections and severe infections. According to the US Centers for Disease Control and Prevention (CDC), COVID-19 vaccination significantly reduced COVID-19 mortality, especially when messenger ribonucleic acid (mRNA)-based vaccines were used.

Most of Thailand’s population is vaccinated inactivated vaccineonly a small proportion received mRNA vaccines as booster vaccines.

The emergence of the SARS-CoV-2 Omicron variant in Thailand has led to a surge in daily infections, reaching nearly 50,000 per day. However, the number of deaths from SARS-CoV-2 infection remained low at around 120 daily.

Scientists have previously hypothesized that: herd immunity Majority of the population may be vaccinated or develop after recovering from COVID-19. However, the emergence of new mutants and reluctance to vaccine have prevented reaching the threshold of herd immunity.

A UK study has created the concept of ‘hybrid immunity’, which refers to the protection conferred by COVID-19 vaccination and natural infection. Previous studies have shown that hybrid immunity can protect individuals from symptomatic infections.

About research

New research under review in the Scientific Reports journal, currently Research Square* According to the preprint server, scientists hypothesize that the lower mortality in COVID-19 patients may be due to hybrid immunity and reduced severity of Omicron infections.

The current study included 79 participants from 15 families enrolled in the Bangkok Home Health Service database between 1 August 2021 and 31 August 2021. In this study cohort, 34 had recovered from her COVID-19 at least 4 weeks prior to his enrollment. , her remaining 45 participants had been in close contact with her COVID-19 patient.

Survey results

T cell responses to neuromyelitis optica (NMO) antigen were detected by interferon release assay in 11 of 45 close contacts 6 months after SARS-CoV-2 exposure. Her asymptomatic COVID-19 rate was estimated at 24.4%.

SARS-CoV-2 receptor binding domain (RBD) immunoglobulin G (IgG) antibody levels and T cell responses to SARS-CoV-2 spike protein, after a second COVID-19 vaccination was associated with comparable immunity between COVID-19 patients and close contacts. Therefore, participants who received her COVID-19 booster vaccination without her previous COVID-19 history also benefited from hybrid immunity.

Antibody responses to RBD IgG (Figure 2A) showed a correlation between antibody levels and neutralizing capacity against the alpha variant of SAR-CoV-2 virus (R = 0.5571, P < 0.0001). Figure 2B shows the levels of RBD IgG in close contacts of COVID-19 patients according to the number of vaccinations. NT = neutralizing antibody, RBD IgG = SARS-CoV-2 receptor binding domain immunoglobulin G, AU/ml = arbitrary units per milliliter.

Similar levels of immunity were observed among individuals in close contact with asymptomatic and symptomatic infected persons.

Previously, no long-term observational data on reinfection rates in individuals exposed to SARS-CoV-2 were available. In the current study, no participants were reinfected with SARS-CoV-2 during enrollment.Figure 3.

Immune responses to SARS-CoV-2 viral antigens compared between close contacts with and without asymptomatic infection, antibody response (RBD IgG) P = 0.1922 t = 1.325, df = 43 (Figure 3A), spike protein P = 0.5325, t = 0.6293, df = 43 (Figure 3B). RBD IgG = SARS-CoV-2 receptor binding domain immunoglobulin G, AU/ml = arbitrary units per milliliter.

Most study participants had received heterologous COVID-19 booster vaccinations, including viral vector vaccines, inactivated vaccines, and mRNA vaccines. To this end, decreased T-cell responses to spike protein and elevated RBD IgG levels were observed after booster vaccination.

After a short period of depletion, T cells may recover 3 months after receiving a COVID-19 booster dose. This observation is consistent with previous studies reporting retention of effective immune responses after heterologous immunization against Omicron variants.

Previous studies have revealed that individuals may have varying levels of cellular and humoral immune responses during similar viral infections. Because the majority of study participants received the mRNA vaccine as a booster dose, T-cell function may be altered after vaccination.

Therefore, the authors strongly recommend multiple booster doses of the COVID-19 vaccine only for immunocompromised individuals with poor T-cell responses. A T cell-based vaccine could also enhance therapeutic efficacy, especially for these patients.

Conclusion

Current research has revealed that both antibody and cellular responses define COVID-19 immunity in society. Taken together, these responses may confer long-term hybrid immunity after booster vaccination against her symptomatic and asymptomatic COVID-19.

A key limitation of the current study is its small size, which limits the generalizability of the results. Moreover, the immune response was perturbed by vaccination.

*Important Notices

research plaza We publish a non-peer-reviewed, preliminary scientific report and should not be viewed as conclusive, to guide clinical practice/health-related actions, or to be treated as established information.