We are currently faced with the question of how the CoV-2 severity may change in the years ahead. Our analysis of immunological and epidemiological data on endemic human coronaviruses (HCoVs) shows that infection-blocking immunity wanes rapidly, but disease-reducing immunity is long-lived.
Our model, incorporating these components of immunity, recapitulates both the current severity of CoV-2 and the benign nature of HCoVs, suggesting that once the endemic phase is reached and primary exposure is in childhood, CoV-2 may be no more virulent than the common cold.
We predict a different outcome for an emergent coronavirus that causes severe disease in children. These results reinforce the importance of behavioral containment during pandemic vaccine rollout, while prompting us to evaluate scenarios for continuing vaccination in the endemic phase.
If frequent boosting of immunity by ongoing virus circulation is required to maintain protection from pathology, then it may be best for the vaccine to mimic natural immunity insofar as preventing pathology without blocking ongoing virus circulation.
Preliminary results suggest the adenovirus-based vaccine is better at preventing severe than mild or asymptomatic infections, and it will be important to collect similar data for the other vaccines.
Should the vaccine cause a major reduction in transmission, it might be important to consider strategies that target delivery to older individuals for whom infection can cause higher morbidity and mortality, while allowing natural immunity and transmission to be maintained in younger individuals.
The findings presented here suggest that using symptoms as a surveillance tool to curb the virus’s spread will become more difficult, as milder reinfections increasingly contribute to chains of transmission and population level attack rates.
In addition, infection or vaccination may protect against disease but not provide the type of transmission-blocking immunity that allows for shielding or the generation of long-term herd immunity.