Researchers in Brazil have reported cases of patients infected with two coronavirus variant strains at once, amid efforts to track the spread of emerging variants across the country.

The findings were posted ahead of peer review this week in the preprint server medRxiv.

The infections were found in two patients in their 30s, who both recovered without requiring hospitalization. One developed a cough and the other experienced a headache, cough and sore throat.

"We were the first to identify two independent events of co-infection caused by the occurrence of B.1.1.28 (E484K) with either B.1.1.248 or B.1.91 lineages," study authors wrote.

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The Brazil P.1 variant is a branch of the B.1.1.28 lineage, according to the Centers for Disease Control and Prevention (CDC), with the first U.S. case of the P.1 variant identified in Minnesota earlier this week. 

The team of researchers warned that co-infections can give way to a faster emergence of strains.

"These co-infections can generate combinations and generate new variants even more quickly than has been happening," the study’s lead researcher Fernando Spilki, a virologist at Feevale University in Rio Grande do Sul state, told Reuters.

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Spilki said co-infections present an additional evolutionary pathway for the novel virus. He added that the cases highlight a surging pandemic in Brazil, because co-infections can only arise under a high degree of transmission.

Of note, the E484K mutation on the virus' spike protein previously showed to escape the neutralization power by antibodies in convalescent plasma treatment, though those findings were preliminary.

"Nevertheless, limited resources and the few number of samples sequenced in Brazil challenges the continuous monitoring of viral evolution and appearance of novel mutations in the country," study authors wrote.