COVID-19 Reinfections in Mexico City: Implications for public health response

Background SARS-CoV-2 pandemia continues to be important even when more than 60% of the global population has been vaccinated. As the pandemia evolves the number of reinfection cases will continue to increase as new variants are generated that evade the immune response. Understanding reinfections is important to guide the public health system and to inform decision-makers. Methods We downloaded clinical outcome and severity of infection data from the SISVER (respiratory disease epidemiological surveillance system) database. We sequenced SARS-CoV-2 samples, identified SARS-CoV-2 lineage and upload this genomic data to GISAID. We analyzed time and lineage between index infection and reinfection. We also analyzed the clinical outcome, severity of infection and vaccination status during reinfections. Findings In this study we confirmed that each wave of SARS-CoV-2 infections was characterized by a different viral variant showing a prevalence higher that 95%. We found that the fraction of reinfection is not linearly related to the average time of separation between waves with 40% of all the reinfections occurring at wave 5, the only wave with more than one SARS-CoV-2 variant with a prevalence higher than 80%. Regarding type of care 2.63% patients were considered ambulatory during the reinfection even when they were hospitalized during the index infection and only 0.78% presented the opposite behavior. Moreover, 6.74% reinfections transitioned from asymptomatic to mild or severe or from mild to severe; and 8.95% transitioned from severe to mild or asymptomatic or from mild to asymptomatic. The highest number of reinfections have occurred in unvaccinated patients (41.6%), followed shortly by vaccinated patients (31.9%). However, most reinfections occurred after wave 4 when the national vaccination efforts have reached 65% of the general population. Interpretation The analyzed data suggests a diminished severity of infection during reinfection either if transitions in disease severity or transitions in type of patient care are considered. Finally, we also observed an overrepresentation of unvaccinated patients in reinfections. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was funded by the Secretaria de Educacion, Ciencia, Tecnologia e Innovacion de la Ciudad de Mexico (SECTEI), SECTEI/223/2021. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the ethics and research committees of the Instituto Nacional de Medicina Genomica (CEI/1479/20 and CEI 2020/21). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced of SARS-CoV-2 cases sequenced by INMEGEN are deposited in GISAID.