SARS-CoV-2 infection episodes by emerging variants in previously naturally infected or vaccinated individuals are already a real phenomenon worldwide which poses an important issue to understand the human immune response to the virus and vaccines.

Reinfection cases have been rising profoundly since the Omicron variant of SARS-CoV-2 started to disseminate in November 2021.

On March 12, 2020, the first case of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was diagnosed in Rio Grande do Norte, northeast Brazil; following that, the pattern of COVID-19 followed the several waves found elsewhere.

Those waves were mostly caused by SARS-CoV-2 virus mutations, which resulted in the emergence of dangerous subtypes (VoC).

Understanding the kinetics of the protective immune response against SARS-CoV-2 has been difficult due to the introduction of new VoCs in a population with prior SARS-CoV-2 infections or after vaccination.

The goal of this research was to look at a SARS-CoV-2 reinfection outbreak that occurred in mid-January 2022 in Rio Grande do Norte, Brazil, after the omicron variant was detected.

Between March 2020 and mid-February 2022, 58,097 people with mild to severe respiratory symptoms tested positive for SARS-CoV-2, out of a total of 172,965 people.

Two positive RT-qPCR confirmations within 90 days of each other, clinical signs similar to COVID-19, positive viral culture, and further viral RNA sequencing from both episodes demonstrating separate strains were all required for a SARS-CoV-2 reinfection case.

444 people who had previously been infected got a second SARS-CoV-2 infection, and 9 of these reinfection cases were chosen for sequencing.

Three participants received a booster, and after the third/additional dosage, they developed symptomatic COVID-19, just like those who had received two doses and had a history of COVID 19.

The genomic analysis found that virus lineages diverged between primary and reinfection, with the latter being caused by the Omicron (BA.1) variant in people who are fully vaccinated.

After confirming that all subjects sequenced had prior SARS-CoV-2 infection and were also fully vaccinated, the findings indicate that the Omicron variant evades natural and vaccine-induced immunity, affirming the ongoing need to reduce transmission and develop effective blocking vaccines.

This highlights the need for more effective vaccines that have the ability to reduce transmission while also providing a longer protective immune response.

The study authors concluded: “Our data suggest that the Omicron variant evades immunity provided from either natural infection from any other SARS-CoV-2 variants or from different types of vaccines.”

The findings of the study were published on the preprint server medrixv.org.

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*Important Note: Since medRxiv publishes preliminary scientific studies that have not been peer-reviewed, they should not be regarded as conclusive, should not be used to direct clinical practice/health-related behavior, and should not be seen as established information.