A study published in The Lancet, which charted the first confirmed case of COVID-19 reinfection in the United States, has raised questions over immunity from the novel coronavirus.

The 25-year-old Nevada man - the patient in question - tested positive for COVID-19 first on 18 April and the second time on 5 June, separated by two negative tests done during a follow-up in May. Genomic analysis of the virus showed genetically significant differences between each variant associated with both instances of infection.

Importantly, the patient showed increased symptom severity in their second infection, which is similar to what was observed in the reinfection case in Ecuador, but contradictory to the respective cases seen in the Netherlands and Hong Kong, where both the first and the second infection were equally severe in the two individuals.

The authors note some possible reasons that could have led to an increased severity the second time:

• First, a very high dose of the virus might have led to the second instance of infection and induced more severe disease.
• Second, it is possible that reinfection was caused by a version of the virus that was more virulent, or more virulent in this patient’s context.
• Third, a mechanism of antibody-dependent enhancement might be the cause, a means by which specific Fc-bearing immune cells become infected with virus by binding to specific antibodies. This mechanism has been seen previously with the betacoronavirus causing severe acute respiratory syndrome. In that case, the patient recovered and was discharged from hospital.
• It is possible that they reported a case of continuous infection entailing deactivation and reactivation. However, for such a hypothesis to be true, a mutational rate of SARS-CoV-2 would be required, and that has not yet been recorded.

“The patient’s immune reaction in vitro was not assessed and, thus, conclusions cannot be made about the duration or degree of immunity,” the researchers add.

What Does This Mean for a COVID-19 Vaccine?

At least four cases of reinfection have been confirmed around the world, which suggests that previous exposure to the virus does not guarantee total immunity, the study notes. These are important things to consider in reaching definite conclusions about the duration for which vaccines will be effective and how often people may need subsequent or booster doses.

Even though vaccines continue to remain crucial in our fight against the virus, following all other precautions such as washing hands, wearing masks and maintaining distance remains non-negotiable with looming questions of COVID-19 immunity and how long it lasts.