M Gabriela M Gomes Profile picture
Biomathematician modeling individual variation in population dynamics
Κασσάνδρα Παρί پری Profile picture phal Profile picture Rogier v Vlissingen 🇳🇱 Profile picture Potato Of Reason Profile picture Arvo Pärt Profile picture 5 subscribed
May 16, 2022 7 tweets 2 min read
#epitwitter Just heard from JTB that our #COVID19 paper was the most downloaded in last 90 days. I plan to spend summer developing projects that build on same concepts and methods. Happy to accommodate collaborations with those interested. Just send note.
journals.elsevier.com/journal-of-the… Broader scope viewpoints article outlining effects and inferences of unobserved variation in disease dynamics just updated on arXiv: arxiv.org/abs/2009.01354
Feb 18, 2022 16 tweets 4 min read
1/14 Dear #epitwitter,
Our first peer reviewed #COVID modelling paper has just been made available online by the grand classic Journal of Theoretical Biology 🙏authors.elsevier.com/sd/article/S00…
Others will follow shortly I believe. 2/14 Joined this platform in June 2019 to say some forms of individual variation impact epidemic dynamics hugely. Not all variation matters and explanation isn’t "nonlinearities this and that". Key process can be described linearly, intuitively, and quantifiably by inference.
Feb 15, 2022 8 tweets 5 min read
Almost 2 years since our low-HIT (herd immunity threshold) preprint was released the paper has been peer reviewed and accepted for publication in a scientific journal (specific details soon).

The accepted version features #COVID19 in England/Scotland: medrxiv.org/content/10.110… Following the initial preprint submitted to medRxiv in April 2020 the theory that individual variation in susceptibility and exposure (frailty variation) to infection lowers HIT and epidemic final size was featured in many news and science outlets, eg:
Jan 2, 2022 5 tweets 2 min read
Case fatality rate em PT e UK desde que PT atingiu 85% da população vacinada com 2 doses (UK tinha 65%): Percentagem com 2 doses em PT e UK:
Jan 2, 2022 4 tweets 1 min read
New Year's resolution for me: No more thinking about COVID-19. Research objectives fulfilled, time for new topics.

Still polishing final writings but worthwhile thinking has been completed

Early conclusions (first released 27 April 2020) remain unchanged
medrxiv.org/content/10.110… Two years ago had privilege to be: offered/accepting Global Talent Research Professorship at Strathclyde University @StrathMathStat; awarded Habilitation from Porto University. Both in recognition for research/teaching variation/selection in epidemiology/ecology/evolution.
Dec 20, 2021 25 tweets 8 min read
Dreaming about death; got up to make coffee

Then decided to write thread about what's killing me. Not depressing (on contrary). It's my duty to make the world understand this +ve thing before I die [not that I think I'll die soon; that was just in dream]

PLEASE READ IF YOU CAN! For more than 10 years I've been researching with collaborators (including @mlipsitch @GrahamMedley) why epidemic models tend to exaggerate epidemic sizes and overestimate intervention impacts (particularly vaccines but also NPIs):
journals.plos.org/plospathogens/…
Dec 18, 2021 14 tweets 2 min read
1/ Many times I have been asked why communication around herd immunity threshold (HIT) was so confusing in this pandemic. I have even been asked whether experts really understand it. Here is my answer: 2/ The concept is well understood among mathematical epidemiologists. In my view what went terribly wrong was the politicised way in which the HIT was used in this pandemic.
Dec 17, 2021 7 tweets 2 min read
Last year, prominent modelling groups dismissed our Covid work (known for incorporating individual variation in susceptibility and exposure, and estimating low herd immunity thresholds) by claiming our stylised contact-reduction profile (Rc) wasn't close to government NPIs.. England and Scotland (with our latest stylised Rc):
Dec 16, 2021 5 tweets 1 min read
No inicio da pandemia convidaram-me para integrar um daqueles grupos que fazem modelos Covid para o governo Portugues. Eu disse que nao porque queria testar um novo conceito de modelos e queria estar a vontade para fazer ciencia pura e comunicar a vontade. Comecei a ser contatada por jornalistas que me faziam perguntas as quais eu respondia avisando sempre que os meus modelos eram diferentes dos clássicos.
Nov 28, 2021 9 tweets 2 min read
Much is being said about Covid variants spreading sequentially faster. A couple of days ago I posted a comment on this in response to @jburnmurdoch
As we approach endemicity new variants are expected to outcompete others faster. Reason being recovered subpopulation (less immune to novel variants as long as there is some immune escape) grows as we approach endemicity increasing the benefit of novelty.
Illustration from model:
Nov 24, 2021 8 tweets 1 min read
Tweet que e cada vez menos novidade mas infelizmente ainda nao totalmente esclarecido principalmente em Portugal:
Levando em conta heterogeneidades realistas na susceptibilidade/exposição ao SARS-CoV-2 o limiar da imunidade de grupo para linhagens iniciais tera sido menos de 30%. Se nao tivessem emergido variantes mais transmissíveis nem vacinas (como se equacionava ha mais de 1 ano) estes limiares teriam sido ultrapassados no inverno passado. Vale o que vale mas cada vez temos mais argumentos a suportar esta afirmação.
Sep 6, 2021 8 tweets 2 min read
1/7
Has the herd immunity threshold (HIT) been used sensibly in the Covid19 pandemic? No! Why does that matter? 2/7
An epidemic (with several waves) may last longer than expected because: (1) it had high potential to begin with and mitigation prevented it from growing vertically so it grew horizontally (single HIT number thinking); or...
Aug 24, 2021 23 tweets 4 min read
Don't know how common this feeling is among mathematical epidemiologists but as someone who has worked on population dynamics of infection & immunity for 20 years I felt hopeless to see herd immunity threshold (HIT) concept degenerating in front of my eyes during pandemic. Thread 1/n
HIT is an abstract concept essential to our work but it was hijacked early in the Covid-19 pandemic and disseminated with all sorts of distortions that prevented the impact of its application by those qualified.
May 27, 2021 8 tweets 3 min read
Our newest #COVID19 paper (with Marcelo Ferreira @ChikinaLab @WesPegden @rjaaguas) is on medRxiv. Individual variation models applied to England and Scotland.

Frailty variation models for susceptibility and exposure to SARS-CoV-2 medrxiv.org/content/10.110… With 20% of their populations immunised by natural infection and their vulnerable vaccinated, many countries, like England and Scotland, appear to be in a comfortable position to redirect remaining vaccines to more susceptible regions.
Dec 24, 2020 6 tweets 2 min read
1/ I want to share a special moment with all who happen to be looking this way. This is the happiest I've been since April 27, when I posted on medRxiv a preprint with title "Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold". 2/ In that preprint we study two mathematical models of the COVID-19 pandemic: one accounting for individual variation in susceptibility to infection; the other accounting for individual variation in exposure to infection (heterogeneous connectivity).
Dec 9, 2020 11 tweets 2 min read
TWIMC: I've been Mathematician and Mother for ~30 years (now also Grandmother) and this is what matters. I spent the last 10 years studying individual variation on characteristics that are under selection but that have no heritability repercussions in the time scale under study. In these studies I have "used" (please make a note of this word) primarily host-pathogen systems but my curiosity for completely different systems was particularly vivid last year and I was happily moving away from infectious diseases when the pandemic started.
Oct 4, 2020 4 tweets 2 min read
1/ Reducing transmission is not the only way of preventing deaths. From health records we can predict who is at risk of severe or fatal disease (medrxiv.org/content/10.110…, PLoS Medicine in press) and offer them shielding. 2/ Shielding was less than optimal in the first wave, because (at least in Scotland) it was implemented too late. But we are better prepared now.
Oct 4, 2020 4 tweets 1 min read
1/ Heterogeneous susceptibility and exposure to infection are under selection by the force of infection. Highly susceptible and highly connected individuals tend to be infected earlier and removed from the susceptible pool earlier. 2/ Mean susceptibility and mean connectivity in residual susceptible pool decrease over time lowering cumulative attack rate (CAR). Models that do not account for complete variation in those characteristics are biased towards overpredicting CAR and herd immunity threshold (HIT).
Sep 29, 2020 4 tweets 1 min read
1. The evidence favouring the heterogeneity model over the homogeneity model is overwhelming, whether we base this on fit penalized by complexity (DIC or similar criteria), forward predictive performance, or the Bayes factor. 2. We show that decreasing mean IFR to 0.3%, consistent with recent estimate for England, does not change fit of the model or inference that slowing and reversal of epidemic was largely attributable to build-up of herd immunity but gives a more plausible value of 15% for the HIT.
Sep 28, 2020 5 tweets 2 min read
Latest on individual variation in susceptibility or exposure to #SARSCoV2 and #COVID19 with Marco Colombo, Joe Mellor, Helen Colhoun and Paul McKeigue:
Trajectory of COVID-19 epidemic in Europe medrxiv.org/content/10.110… We show that relaxing the assumption of homogeneity in the modelling code released by Flaxman et al (Nature) to allow for individual variation in susceptibility or connectivity gives a model that has better fit to the data and more accurate 14-day forward prediction of mortality.
Sep 19, 2020 9 tweets 7 min read
@PieterTrapman @mlipsitch 1/ Unclear what you mean by these numbers, but a week later I finally had a couple of hours on a Saturday to have a look. Running the models in our July preprint I am now comparing the 70% lower-risk group with the whole population. Here is what I find (explanations follow). @PieterTrapman @mlipsitch 2/ I run each of the 3 models until the pandemic is over (one year is sufficient for these models). Then I calculate the proportion of the 70% lower-risk group that has been infected and divide by the portion of the entire population that has been infected.