Dynamic causal modeling for the future projection of the COVID-19 pandemic
The onset of the 2019 coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused more than 4.85 million deaths worldwide. Most scientists around the world agree that the most effective method to end the current pandemic is vaccination.
Therefore, the search for a suitable vaccine against SARS-CoV-2 has led to the development of several vaccine candidates. These vaccines have undergone various series of clinical trials before they can be administered to humans on a large scale.
Following the rollout of the vaccine in the UK, many have chosen to forgo public health control measures such as social distancing and wearing masks. Thus, the current situation in the UK provides a natural experience for other countries to assess their own public interventions.
Study: A twelve-month projection to September 2022 of the Covid19 epidemic in the UK using a dynamic causal model. Image Credit: NicoElNino / Shutterstock.com
New study published on the preprint server medRxiv * uses dynamic causal modeling (DCM) to predict the effects of letting SARS-CoV-2 sweep through a widely vaccinated population. DCM combines epidemiological models with behavioral modeling at the population level. Therefore, DCM’s forecasts could provide a baseline for other countries to help them monitor the effects of their public health control measures.
About the study
The current study involved DCM which had certain advantages, as these models could continuously assimilate data as well as modify model parameters such as changes in social distancing, virus transmissibility and vaccination coverage. The model also provides up-to-date projections and estimates, is fully described, includes all standard sensitive, exposed, infected, suppressed (SEIR) data, as well as interactions between variables.
The standard SIER models depend on the choice of parameters, which requires assumptions, while the DCM model is without assumptions. The model is accurate enough to model the past stages of the pandemic, as well as predicting what will happen if everything continues as before.
The current study also included data from Public Health England (PHE) and the COVID-19 Infection Survey of the Office of National Statistics (ONS). Several assumptions are made in the study, such as the lockdown will not be reimposed, no mitigation efforts will take place in schools, no new variants of the virus will arise despite few travel restrictions and porous borders, and the Alpha variant is 50% more transmissible than the original variant while the Delta variant is 50% more transmissible than the Alpha variant.
The study also involved an estimation of the vaccine’s efficacy regarding transmission, pathogenicity, mortality and protection against infection. For this, prior estimates derived from the ONS study and the mortality from the PHE study were required. The various vaccines in use in the UK until September 15, 2021 included the ChAdOx1, BNT162b2 and mRNA1273 (Moderna) vaccines, which respectively accounted for 53%, 45% and 3% of all vaccines distributed across the UK.
Three different scenarios were presented in the study. The first (NPI1) provided projections with basic parameters, the second (NPI2) improved the identification, test, traceability, isolation and care system (FTTIS) from 30 to 50% , and the third (NPI3) improved the FTTIS system by 80%. .
The results of the present study indicated that the vaccines were very effective in reducing mortality and morbidity; however, they were not as effective at reducing transmission. The model suggested that the loss of immunity occurred in 284 days, which was similar to the results of the ONS study. Therefore, booster doses of the vaccines may be necessary.
The model also predicted that despite effective vaccinations, the UK could expect another significant wave of COVID-19 that could lead to 3 million cases of post-COVID-19 syndrome, 150,000 hospitalizations and 300 million people. additional tests. If, alongside vaccination, other public health mitigation measures were used, the possibility of a future wave could be eliminated.
In addition, the lack of border controls and few travel restrictions will allow new variants to enter and invade the UK. This would have a negative impact on the already overburdened health system. Also, the absence of public health measures will lead to the emergence of future variants which would reintroduce more restrictive confinements.
UK epidemic curve projections – incidence rate, daily confirmed cases and incidence of long-Covid to March or September 2022.
Therefore, the lessons for other countries are quite clear. No country should depend on vaccination alone to prevent the spread of SARS-CoV-2.
In addition, the relaxation of public health measures has several negative impacts including a new overload of the health system, the emergence of vaccine-resistant variants and significant economic costs due to a large number of cases. Thus, in parallel with vaccination, public health measures must be continued to prevent any new epidemic of COVID-19.
medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.