On March 11, 2020, the World Health Organization declared the global outbreak of SARS-CoV-2 infection, known as COVID-19, a pandemic. A recent report identifies the immunological characteristics of SARS-CoV-2 that will govern its transition from pandemic to endemic status.
The epidemiological view of endemic disease is one that is continuously, predictably present in the human population. An endemic disease is in a steady state in which the infection does not die out and the number of infected people does not increase exponentially.
The SARS-CoV-2 virus, the cause of COVID19, is one of seven coronaviruses known to infect humans. Four of these human coronaviruses are globally endemic and elicit mild symptoms, while the remaining two, SARS-CoV (which causes severe acute respiratory syndrome, or SARS) and MERS-CoV (which causes Middle East respiratory syndrome, or MERS), are associated with more severe disease outcomes and death.
The authors of the report developed an epidemiological model based on key aspects of immunity, all of which centered on reinfection. These aspects included how susceptible a population is to reinfection, whether the disease weakens after reinfection, and how quickly the virus spreads after reinfection.
The authors' analysis suggested that once SARS-CoV-2 becomes endemic, the disease profile will look considerably different than it does now, affecting primarily children, eliciting mild symptoms, and providing immunity against severe outcomes with future reinfection. In this scenario, vaccination might not be required. However, the current vaccines against SARS-CoV-2 will play a role in how fast the virus becomes endemic, especially if they induce short-lived immunity but reduce the severity of disease upon reinfection. The authors posited that as milder reinfections become more common, reliance on symptoms as a surveillance tool to curb the virus’s spread will become more difficult.
These findings suggest that in the coming years SARS-CoV-2 infection will become endemic, but until then, public health containment strategies such as wearing masks and social distancing remain essential.
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