Conclusion

In summary, the observation that, compared with other respiratory viruses, children have less severe symptoms when infected by SARS-CoV-2 is surprising and not yet understood. Furthermore, it is also uncertain why children with the usual risk factors for infections, such as immunosuppression, are not at high risk for severe COVID-19, while previously healthy children can on rare occasions become severely ill.110–113 222 Although there are several hypotheses for why children are less affected by COVID-19, with the notable exception of age-related changes in immune and endothelial/clotting function, most do not explain the observed age-gradient in COVID-19 with severity and mortality rising steeply after the age of 60 to 70 years. Unravelling the mechanisms underlying the age-related differences in the severity of COVID-19 will provide important insights and opportunities for the prevention and treatment of this novel infection.