Characteristics of Persons With Secondary Detection of Severe Acute Respiratory Syndrome Coronavirus 2 ≥90 days After First Detection, New Mexico 2020

Protection of hybrid immunity against SARS-CoV-2 reinfection and severe COVID-19 during periods of Omicron variant predominance in Mexico

Background

With the widespread transmission of the Omicron SARS-CoV-2 variant, reinfections have become increasingly common. Here, we explored the role of immunity, primary infection severity, and variant predominance in the risk of reinfection and severe COVID-19 during Omicron predominance in Mexico.

Methods

We analyzed reinfections in Mexico in individuals with a primary infection separated by at least 90 days from reinfection using a national surveillance registry of SARS-CoV-2 cases from March 3rd, 2020, to August 13th, 2022. Immunity-generating events included primary infection, partial or complete vaccination, and booster vaccines. Reinfections were matched by age and sex with controls with primary SARS-CoV-2 infection and negative RT-PCR or antigen test at least 90 days after primary infection to explore reinfection and severe disease risk factors. We also compared the protective efficacy of heterologous and homologous vaccine boosters against reinfection.

Results

We detected 231,202 SARS-CoV-2 reinfections in Mexico, most occurring in unvaccinated individuals (41.55%). Over 207,623 reinfections occurred during periods of Omicron (89.8%), BA.1 (36.74%), and BA.5 (33.67%) subvariant predominance and a case-fatality rate of 0.22%. Vaccination protected against reinfection, without significant influence of the order of immunity-generating events and provided >90% protection against severe reinfections. Heterologous booster schedules were associated with ~11% and ~ 54% lower risk for reinfection and reinfection-associated severe COVID-19, respectively, modified by time-elapsed since the last immunity-generating event, when compared against complete primary schedules.

Conclusion

SARS-CoV-2 reinfections increased during Omicron predominance. Hybrid immunity provides protection against reinfection and associated severe COVID-19, with potential benefit from heterologous booster schedules.

SARS-CoV-2 reinfection and COVID-19 severity

SARS-CoV-2 reinfection rate is low. The relative severity of the first and second episodes of infection remains poorly studied. In this study, we aimed at assessing the frequency of SARS-CoV-2 reinfections and comparing the severity of the first and second episodes of infection. We retrospectively included patients with SARS-CoV-2 positive RT-PCR at least 90 days after clinical recovery from a COVID-19 episode and with at least one negative RT-PCR after the first infection. Whole genome sequencing and variant-specific RT-PCR were performed and clinical symptoms and severity of infection were retrospectively documented from medical files. A total of 209 COVID-19 reinfected patients were identified, accounting for 0.4% of positive cases diagnosed from 19 March 2020 to 24 August 2021. Serology was performed in 64 patients, of whom 39 (60.1%) had antibodies against SARS-CoV-2 when sampled at the early stage of their second infection. Only seven patients (3.4%) were infected twice with the same variant. We observed no differences in clinical presentation, hospitalization rate, and transfer to ICU when comparing the two episodes of infections. Our results suggest that the severity of the second episode of COVID-19 is in the same range as that of the first infection, including patients with antibodies.