Covid-19 cases are on the rise again in Europe, Canada and parts of the United States. Among them, many are wondering whether contracting and recovering from COVID-19 will provide lasting immunity to the disease.

Too many people report being reinfected just weeks or even months after being infected with COVID-19. However, few studies have been done on 2019-nCoV infection to date, and it is unclear whether in these cases the virus disappeared completely, or whether different mutant strains caused the initial infection and reinfection, respectively. Sometimes it’s hard to say no.

The U.S. Centers for Disease Control and Prevention (CDC) has released a report documenting 10 confirmed cases of reinfection with the Omicron strain within 90 days of being infected with the Delta strain of novel coronavirus. In this study, a genetic analysis technique called whole-genome sequencing identified the mutations that were present in the infected individuals in each infection. Cases were collected from four states between October 2021 and January 2022.

Samira Jamie, M.D., Ph.D., program director of the Department of Clinical Immunology and Allergy at the University of Western Ontario, Canada, said, “The compelling theory held for reinfection is that it’s just a long-term shedding of the virus. “So the most striking message of this paper is that whole-genome sequencing identified two separate infections,” he added.

Eight of the 10 patients were under the age of 18 years, and the remaining two were long-term care facility residents and health care workers. The shortest interval between Delta and Omicron infections was just 23 days, experienced by one unvaccinated child aged 12-17 years.

The child was first infected with the Delta strain on November 23, 2021, and the Omicron strain on December 16, 2021. The child had symptoms during the first infection but was asymptomatic during the second.

On the other hand, of the remaining seven children who were briefly infected with the Delta and Omicron strains, six developed symptoms with both infections. All of these children were between the ages of 5 and 11, and one child had symptoms during the first infection, but no data were available on symptoms during the second infection.

All children were unvaccinated at the time of infection with the Delta strain. Also, only two had received the first dose of vaccine before experiencing a second infection with the Omicron strain.

“While this is a concern, it is not surprising that the majority of reinfections occur among people whose vaccinations are likely suboptimal,” Jamie said. “The unvaccinated or incomplete vaccination status of reinfected individuals demonstrates the continuing importance of mass vaccination efforts,” Jamie said.

With so few cases undergoing whole-genome sequencing in the United States, it is difficult to confirm different variants and identify reinfections. That’s why the study included only 10 people.

The paper also notes that as more people rely on rapid antigen tests and self-diagnose at home, obtaining samples for sequencing is becoming increasingly difficult. It’s unclear how many people actually get reinfected within 90 days, but it’s certainly more than the CDC report found.

The original variant of the novel coronavirus was thought to confer immune protection against viral infection for at least 90 days after infection. Some were even exempt from required tests and proof of vaccination by submitting evidence of positive test results within 90 days. But newer strains of the novel coronavirus have emerged, making reinfection even more likely.

Delta strains faded in many parts of the world, including Europe and the US, and were replaced by Omicron strains BA.1 and BA.2. Because these variants are relatively new and have only started infecting many people in the last few months, little is currently known definitively about reinfection with them.

A small Danish study published as a pre-peer-reviewed paper in February identified 67 people who were infected twice with the Omicron strain between 20 and 60 days. More than two-thirds of the cases were initially infected with Omicron strain BA.1 and then with BA.2. Most of those infected were unvaccinated young people. This is similar to a smaller CDC study of cases of Delta followed by Omicron.

Although it is difficult to draw conclusions from studies with small numbers of participants, the authors of the CDC report noted that the majority of reinfections occurred among unvaccinated children.

The authors stated: “To maximize prevention of reinfection and spread, all eligible persons should be vaccinated without delay, including boosters where appropriate, and avoid exposure or symptoms of COVID-19.” If it comes out, it should be retested,” he said.

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