Epidemiological and evolutionary considerations of SARS-CoV-2 vaccine dosing regimes

• Published in: Science (American Association for the Advancement of Science) Vol. 372; no. 6540; pp. 363 - 370
• Main Authors: Saad-Roy, Chadi M., Morris, Sinead E., Metcalf, C. Jessica E., Mina, Michael J., Baker, Rachel E., Farrar, Jeremy, Holmes, Edward C., Pybus, Oliver G., Graham, Andrea L., Levin, Simon A., Grenfell, Bryan T., Wagner, Caroline E.
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 23.04.2021; American Association for the Advancement of Science
• Subjects: Adaptation; Adaptation, Physiological; Adaptive Immunity; Antigens; Coronaviridae; Coronaviruses; COVID-19; COVID-19 - epidemiology; COVID-19 - immunology; COVID-19 - prevention & control; COVID-19 - virology; COVID-19 Vaccines - administration & dosage; COVID-19 Vaccines - immunology; Disease control; Disease Susceptibility; Disease transmission; Dosage; Epidemic models; Epidemiology; Evolution; Evolution, Molecular; Feedback (Response); Herd immunity; Host selection; Humans; Immune Evasion; Immune response; Immune system; Immunity; Immunization; Immunization Schedule; Immunogenicity, Vaccine; Immunology; Infections; Jurisdiction; Models, Theoretical; Mutation; Pandemics; Public policy; Respiratory diseases; Robustness; SARS-CoV-2 - genetics; SARS-CoV-2 - immunology; Selection, Genetic; Severe acute respiratory syndrome coronavirus 2; Shortages; Vaccination; Vaccines; Viral diseases
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.abg8663

For two-dose vaccines against severe acute respiratory syndrome coronavirus 2, some jurisdictions have decided to delay the second dose to rapidly get the vaccine into more people. The consequences of deviating from manufacturer-prescribed dosing regimens are unknown but will depend on the strength of immune responses to the vaccines. Saad-Roy et al. took a modeling approach to tackling the inevitable uncertainties facing vaccine rollout. The authors found that although one-dose strategies generally reduce infections in the short term, in the long term, the outcome depends on immune robustness. A one-dose strategy may increase the potential for antigenic evolution if immune responses are suboptimal and the virus continues to replicate in some vaccinated people, potentially leading to immune-escape mutations. It is critical to gather serological data from vaccinated people and, to avoid negative outcomes, to ramp up vaccination efforts worldwide. Science , this issue p. 363 A one-dose vaccine policy may increase the potential for viral antigenic evolution in some scenarios. Given vaccine dose shortages and logistical challenges, various deployment strategies are being proposed to increase population immunity levels to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Two critical issues arise: How timing of delivery of the second dose will affect infection dynamics and how it will affect prospects for the evolution of viral immune escape via a buildup of partially immune individuals. Both hinge on the robustness of the immune response elicited by a single dose as compared with natural and two-dose immunity. Building on an existing immuno-epidemiological model, we find that in the short term, focusing on one dose generally decreases infections, but that longer-term outcomes depend on this relative immune robustness. We then explore three scenarios of selection and find that a one-dose policy may increase the potential for antigenic evolution under certain conditions of partial population immunity. We highlight the critical need to test viral loads and quantify immune responses after one vaccine dose and to ramp up vaccination efforts globally.