SARS-CoV-2 infection-induced immunity reduces rates of reinfection and hospitalization caused by the Delta or Omicron variants

Abstract

During a pandemic, effective vaccines are typically in short supply, particularly at onset intervals when the wave is accelerating. We conducted an observational, retrospective analysis of aggregated data from all patients who tested positive for SARS-CoV-2 during the waves caused by the Delta and Omicron variants, stratified based on their known previous infection and vaccination status, throughout the University of Texas Medical Branch (UTMB) network. Next, the immunity statuses within each medical parameter were compared to naïve individuals for the effective decrease of occurrence. Lastly, we conducted studies using mice and pre-pandemic human samples for IgG responses to viral nucleocapsid compared to spike protein toward showing a functional component supportive of the medical data results in relation to the immunity types. During the Delta and Omicron waves, both infection-induced and hybrid immunities were associated with a trend of equal or greater decrease of occurrence than vaccine-induced immunity in hospitalizations, intensive care unit admissions, and deaths in comparison to those without pre-existing immunity, with hybrid immunity often trending with the greatest decrease. Compared to individuals without pre-existing immunity, those vaccinated against SARS-CoV-2 had a significantly reduced incidence of COVID-19, as well as all subsequent medical parameters. Though vaccination best reduces health risks associated with initial infection toward acquiring immunity, our findings suggest infection-induced immunity is as or more effective than vaccination in reducing the severity of reinfection from the Delta or Omicron variants, which should inform public health response at pandemic onset, particularly when triaging towards the allotment of in-demand vaccinations.

Impact of National Omicron Outbreak at the end of 2022 on the future outlook of COVID-19 in China

“…Recent studies reported that SARS-CoV-2 infection-induced immunity reduced rates of reinfection and hospitalization caused by later variants [ 7 ]. It is not clear how long such immunity may last but such infection-induced-immunity can supplement vaccine-induced-immunity, by forming the “hybrid immunity” as being described in recent literature [ 8 ].…”

A mini review of reinfection with the SARS‐CoV‐2 Omicron variant

“…The mean pooled effectiveness from past infection was greater than 78% against severe reinfection (hospitalization and death) for all variants, including Omicron BA.1 36 . Both infection‐induced and hybrid immunities could reduce the rates of hospitalizations, intensive care unit admissions, and deaths associated with reinfection, compared to those without pre‐existing immunity 37 …”

“…36 Both infection-induced and hybrid immunities could reduce the rates of hospitalizations, intensive care unit admissions, and deaths associated with reinfection, compared to those without pre-existing immunity. 37 The initial infection or vaccination produces protective antibodies, which should reduce the probability of severe symptoms upon reinfection. Surveillance data from January 2020 to May 2021 in the United Kingdom during the early stage of the SARS-CoV-2 epidemic showed a 61% lower mortality rate for reinfection compared to primary infection.…”

“… 36 Both infection‐induced and hybrid immunities could reduce the rates of hospitalizations, intensive care unit admissions, and deaths associated with reinfection, compared to those without pre‐existing immunity. 37 …”

Beyond the peak: Global health post-COVID-19 and Mpox: Successes, challenges and prospects

“…For example, the combination of natural infection and vaccination has significantly increased global immunity to SARS-CoV-2 as observed in two different reviews [11,12]. The latest data indicates that the decreasing numbers of deaths and hospitalizations can be attributed, in large part, to the high levels of population immunity against SARS-CoV-2 [13]. Similarly, systematic efforts to control Mpox have led to a significant reduction in new cases over the past three months.…”