Alex de Visscher – A rambling mind

They think it’s all over – but it isn’t

Chart 318 for scenario UK_994 with adult vaccinations, and vacs for 5-11 year-olds from April 1st 2022. 24th February NPI -79.64% reduction. Omicron BA.1 transmission k11 = 6. BA.2 k11 = 8, var_eff = 25/50/70%, fSS 3% and fmort 1.05%. Model outcomes to December 3rd 2023. Reported active cases and deaths to 19th April 2022. Serious cases for 5 variants.

In this article, I present a few variations of the current model to illustrate some outcomes depending on different assumptions about the current dominant variant, Omicron BA.2; they are fairly consistent in their forecasts over the 1400 day period of the model, from the outset in February 2020 to December 2023, and show that as NPIs are removed, vaccination is what keeps us safe.

Delta variant impact on June 21st easing – delay or reduce?

Chart 318 for scenarios UK479 and UK465 with vaccinations and 2021 NPI relaxations up to June 21st with 4% and Aug 16th with 2% NPI effectiveness. v3 transmission k11 = 1, var_eff = 100%, fss and fmort as fort v1 and v2. Modelled 800 day outcomes to April 12th 2022 compared with reported active cases and deaths to June 4th. Serious cases for three variants.

Having explored what pandemic advisers might be seeing and highlighting to decision-makers in Government, I run scenarios with different settings for the planned June 21st relaxation of lockdown, the last in the series of relaxations over the first half of 2021, following the January 3rd lockdown. These model scenarios show examples of what the relative consequences of the June 21st relaxation as planned, versus four other options:- cancellation of the June 21st step altogether, two different delays, of 28 and 56 days, and lastly a 50% reduction in the scope of the June 21st relaxation.

What are UK Government advisers seeing?

Recent variants with their identifiers, lineage, source country if known, total cases, and new cases since May 12th: source gov.uk

I have developed some model scenarios that show examples of what might be behind expert advice on the caution required with new SARS-Cov-2 variants. The scenarios indicate the importance of the UK vaccine programme, as we face variants with potentially different characteristics of transmission, severity of infection and responsiveness to vaccines. Understanding those variant characteristics is vital for projections.

Why the UK Government is worried about new variants

Chart 18 for scenarios UK433 & UK439: v3 transmission k11 = 1, comparing var_eff and fss fmort effects. Modelled 800 day outcomes to April 12th 2022 compared with reported deaths to May 23rd. Serious cases for all variants, with 2021 NPI relaxations up to June 21st 2021.

Exploring new variants, vaccines and NPIs

Chart 303 for the grouped model UK929: modelled 800 day outcome for all variants for serious cases and deaths, with 2021 NPI relaxations up to June 21st 2021

There has been increasing concern recently about SARS-Cov-2 variants that might escape vaccines to some extent, as well as having different transmission rates (as the Kent variant does), and causing different severity of illness with higher mortality. I have added a vaccination efficacy modifier, var_eff, by variant, as a multiplier to the standard vaccination efficacy, vac_eff, to help model such potential variants that have a partial or total capability to escape vaccines, and this post shows examples of how that works, using a third variant introduced to the model on January 1st 2021. In addition, I have completed adding fSS (the fraction of people becoming seriously sick from each variant) and fmort (fatality of the variant) by Covid variant.

Tuning the age and vulnerability model

Chart 19 for the grouped model UK957: modelled 800 day outcome compared with reported data to April 21st for active cases and deaths, with 2021 NPI relaxations up to June 21st 2021

In my latest post on March 26th I described a new Coronavirus group model, based on work I had done as a UK case study in support of Prof. Alex de Visscher’s paper, in conjunction with Dr. Tom Sutton, on “Second-wave Dynamics of COVID-19: Impact of Behavioral Changes, Immunity Loss, New Strains, and Vaccination” which has now been published for peer review as a pre-print on Springer’s site at https://www.researchsquare.com/article/rs-195879/v1. I have now added the latest UK vaccination progress figures, and the UK Government’s announced intentions for the near future regarding Non Pharmaceutical Interventions (NPIs). I have also updated mortality and infection characteristics for the four different population groups in the model.

Age and vulnerability related Coronavirus modelling

Chart 209 showing modelled and reported cumulative cases and deaths to 800 days in the groups model

In my most recent post on February 12th, I described modelling work I had done in support of Prof. Alex de Visscher’s paper, in conjunction with Dr. Tom Sutton, on “Second-wave Dynamics of COVID-19: Impact of Behavioral Changes, Immunity Loss, New Strains, and Vaccination” which has now been published for peer review as a pre-print on Springer’s site at https://www.researchsquare.com/article/rs-195879/v1. I have now added vaccination and multiple variants I had already added to our previous model into the new grouped population model, and this blog post reports on progress with that new model.

NPIs, variants and vaccine models

Chart 17 model output for deaths, active cases and Seriously Sick to 800 days. 2nd virus variant from September 23rd, day 235. 3rd variant from January 1st 2021, Day 335. 250k vacs/day from January 1st (day 335) and 400k vacs/day from February 1st (day 366) and thereafter. 15% NPI reduction on March 7th, model Day 401.

This paper reports some parametric Coronavirus model runs I have made that compare, in particular, how the UK vaccine programme allows some NPI relaxation compared with a case with no vaccination. The outcome is that the vaccine programme in the UK has the potential to reduce the imposition of NPIs on March 7th by about 15%, without costing lives, this being the next time we in the UK are due for a major NPI review, potentially involving the return of schools at around March 7th.

Concurrent Coronavirus two variant modelling

New 12-compartment model flowchart with additional vaccination compartment V and repeated Incubation, Sick, Seriously Sick, and Better compartments, all infective, in addition to the Uninfected, Vaccinated, Recovered and Deceased compartments

I present an analysis of the pandemic situation in the UK, with two Coronavirus variants present since December 16th, and sensitivities to different New Year 2021 Non Pharmaceutical Interventions (NPIs), but always with the background of vaccine dispensing, which started in the UK on December 8th.

Exploring the possible impact of the new variant coronavirus

Chart 14 model output to 800 days. Realistic case scenario. New virus variant. Vaccinations start Jan 1st 2021 (Day 335) at 100k/day, at 95% efficacy, rising to 300k/day at 95% efficacy, until April 12th 2022. 10% Dec 16th Intervention enhancement. 20% intervention enhancement after New Year.

I cautiously welcomed “the end of the beginning”, and events since then have borne out the need for caution, with the discovery of a mutant variant of the SARS-Cov-2 virus (denoted VUI-202012/01) which seems to have a much greater transmission rate, as much as 70% more than the strain of SARS-Cov-2 we have seen previously in the UK. I have developed a further version of my Coronavirus model which now includes not only intervention capability but also a vaccination module, as reported before, and now the ability to add further virus strains with different transmission characteristics.