The Delta variant triggers the third wave of COVID-19 in Mexico

Validation and implementation of TaqMAMA RT-PCR for SARS-CoV-2 variant surveillance: experience from a high-volume setting

BACKGROUND

The genomic surveillance of SARS-CoV-2 is challenging in high-volume, resource-limited settings. Faster and less expensive methods are required for the prompt detection of variants of interest. This study aimed to validate and implement the TaqMAMA RT-PCR method for the detection of SARS-CoV-2 variants.

METHODS

We developed the TaqMAMA RT-PCR method for SARS-CoV-2 variants. From the viral genomes obtained from the GISAID database, fluorescent amplification probes and oligonucleotides were designed to detect two specific mutations for each variant. The study consisted of an assay validation phase comparing the newly designed method to WGS in COVID-19-positive samples, followed by a large-scale implementation phase to calculate its performance.

RESULTS

During the assay validation phase, we included 232 samples for analysis using TaqMAMA and WGS. TaqMAMA identified 82.3% as positive, and had sensitivities of 82%, 100%, and 50%, specificities of 91%, 99%, and 100%, with PPVs of 99%, 75%, and 100%, and NPVs of 20%, 100%, and 100% for the Delta, Alpha, and Gamma variants, respectively. For the implementation phase, we included 1315 samples, TaqMAMA identified 68% positive samples, 97.5% as delta. The predicted performance using Bayesian statistics was 95%, 55%, and 0% for the positive, and 29%, 0%, and < 1% for the negative delta, alpha, and gamma variants, respectively.

CONCLUSIONS

The diagnostic performance of TaqMAMA RT-PCR was acceptable for the detection of the most prevalent SARS-CoV-2 variants of interest. This method offers a cost and time-saving alternative for the genomic surveillance of SARS-CoV-2 in high-volume settings.

Omicron and Delta variant prevalence detection and identification during the fourth COVID-19 wave in Mexico using wastewater-based epidemiology

Objectives

To identify the SARS-CoV-2 variants Delta and Omicron during the fourth wave of the COVID-19 pandemic in Mexico using samples taken from 19 locations in 18 out of the 32 states.

Methods

The genetic material concentration was done with PEG/NaCl precipitation, SARS-CoV-2 presence was confirmed by reverse transcriptase-quantitative polymerase chain reaction assay, the variant detection was carried out using a commercial mutation detection panel kit, and variant/mutation confirmation was done by amplicon sequencing of receptor-binding domain target region. The study used 41 samples.

Results

The Delta variant was confirmed in two samples during August 2021 (Querétaro and CDMX) and in three samples during November 2021 (Aguascalientes, Ciudad Juárez campuses, and Nuevo Leon). In December 2021, another sample with the Delta variant was confirmed in Nuevo Leon. Between January to March 2022 only the presence of Omicron was confirmed, (variant BA.1). Additionally, in this period six samples were identified with the status "Variant Not Determined".

Conclusion

To our knowledge, this study is one of the first to identify Omicron and Delta variants with polymerase chain reaction in Mexico and Latin America and its distribution across the country with 56% Mexican states making it a viable alternative for variant detection without conducting a large quantity of sequencing of clinical tests.

Comparative analysis of risk factors for COVID-19 mortality before, during and after the vaccination programme in Mexico

OBJECTIVES

The purpose of this study was to compare case fatality rates (CFRs) and odds for mortality by risk factors of patients with COVID-19 in Mexico, before, during and after the implementation of the national COVID-19 vaccination programme.

STUDY DESIGN

A large database including COVID-19 monitoring cases was used to perform an observational retrospective study.

METHODS

The Chi-squared test and multivariate logistic regression analyses were applied to data from COVID-19-positive patients in Mexico. Data were analysed over 3 years, 2020, 2021 and 2022, corresponding with pre-, during and post-vaccination periods. The unadjusted odds ratios and 95% confidence interval were used to estimate the risk factors for COVID-19 mortality in each of the years.

RESULTS

Statistically significant differences in CFR and odds ratio were found in the studied years, favouring postvaccination period. Significant changes in CFR by age, sex and main comorbidities indicated changes in the epidemic dynamics after the implementation of the COVID-19 vaccination campaign. The likelihood of death increased for hospitalised cases and for patients who were middle-aged or older in 2021 and 2022, whereas the odds of death associated with sex and comorbidities remained similar or reduced over the 3 years.

CONCLUSIONS

Implementation of the COVID-19 vaccination programme during 2021 showed positive consequences on CFR. The increased odds of dying in hospitalised patients are likely to be due to the unvaccinated proportion of patients.