Modeling study examines impacts of one versus two doses of a COVID-19 vaccine

2021-04-16 Hits(74)

As SARS-CoV-2 pandemic continues, vaccine presents a key to mitigate and prevent disease. Pfizer, AstraZeneca are all vaccines have been put in use, including other kinds of operational vaccines require at least two doses. However, Several countries including UK, America and Canada have chosen to delay the second dose in an effort to increase the number of individuals receiving at least one or in response to logistical constraints. Chadi M. Saad-Roy teams’ result had questioned that if this kind of population-scale deviating from manufacturer-prescribed dosing is reliable.  


Research process


To better understand the long-term epidemiological and evolutionary impact of different dosing regimens, the Chadi M. Saad-Roy research team developed an existing epidemiological model of immunity.

Their model included two vaccination groups, one with two doses of vaccine and the other with only one dose, and allowed the immunity produced by the vaccine to wane at different rates, implying that people would be more susceptible to infection at different points in time after vaccination or after natural infection.



Fig. 1 Description of the extended immuno-epidemiological model with one- and two-dose vaccination regimes


The authors focused on vaccines from Pfizer/BioNTech, Modern and Oxford/AstraZeneca, all of which are two-dose vaccines, although they noted that their vaccination methods are universal.

The Saad-Roy team found that while the single-dose vaccine strategy typically reduces the chance of infection in the short term, if the single-dose vaccine produces a weak immune response, this may provide only a short-term marginal benefit, yet at the cost of the virus continuing to replicate in the bodies of some vaccine recipients, which could lead to mutations in the virus that escape immunity.


Fig. 2 Synoptic medium-term immune landscapes and infection burden.


A two-dose strategy could mitigate this effect, they said, but the number of individuals vaccinated would be correspondingly reduced, which would increase the pressure on the rest of the population to infect their load with the virus.


Research Results


Current uncertainties surrounding the strength and duration of adaptive immunity in response to natural infection or vaccination lead to very broad ranges for the possible outcomes of various dosing regimes. Nevertheless, ongoing elevated COVID-19 case numbers stresses the rapid need for effective, mass vaccine deployment. Overall, Chadi M. Saad-Roy research teamemphasized that the impact of vaccine dosing regimes are strongly dependent on the relative robustness of immunity conferred by a single dose. It is therefore imperative to determine the strength and duration of clinical protection and transmission-blocking immunity through careful clinical evaluations in order to enforce sound public policies.