Koronaepidemian mallinnuksen lähtökohdat, tavoitteet ja ongelmat

Terveyden ja hyvinvoinnin laitoksessa (THL) tehtiin keväällä 2020 matemaattisiin malleihin perustuvia skenaarioita SARS-CoV-2-epidemian kulusta olettamalla, että viruksen tartuttavuuslukuun voidaan vaikuttaa eriasteisilla rajaamistoimilla. Lyhyen aikavälin ennusteita viruksen aiheuttaman sairaanhoidon tarpeesta on tehty maaliskuusta lähtien. Esittelemme viruksen tartuttavuusluvun arviointia ja merkitystä epidemian seurannassa sekä kartoitamme immuniteetin roolia epidemian muokkaajana. Tautitaakan ja sairaanhoidon ennusteet perustuvat tartuntojen ilmaantuvuuden mallintamiseen sekä arvioon yksittäiseen tartuntaan liittyvästä vakavan sairastumisen riskistä. Ajantasainen tieto on tärkeää ja matemaattisilla malleilla on monia käyttötarkoituksia. Puutteellinen ymmärrys SARS-CoV-2:n tuottamasta immuniteetista vaikeuttaa toistaiseksi epidemian kulun ennustamista. Mallien tärkein hyöty on auttaa selvittämään tartuntojen, immuniteetin ja epidemian rajaamistoimien yhteistä dynamiikkaa

Infrared fixed point of SU(2) gauge theory with six flavors

We compute the running of the coupling in SU(2) gauge theory with six fermions in the fundamental representation of the gauge group. We find strong evidence that this theory has an infrared stable fixed point at strong coupling and measure also the anomalous dimension of the fermion mass operator at the fixed point. This theory therefore likely lies close to the boundary of the conformal window and will display novel infrared dynamics if coupled with the electroweak sector of the Standard Model.Peer reviewe

Safety versus triviality on the lattice

We present the first numerical study of the ultraviolet dynamics of nonasymptotically free gauge-fermion theories at large number of matter fields. As test bed theories, we consider non-Abelian SU(2) gauge theories with 24 and 48 Dirac fermions on the lattice. For these numbers of flavors, asymptotic freedom is lost, and the theories are governed by a Gaussian fixed point at low energies. In the ultraviolet, they can develop a physical cutoff and therefore be trivial, or achieve an interacting safe fixed point and therefore be fundamental at all energy scales. We demonstrate that the gradient flow method can be successfully implemented and applied to determine the renormalized running coupling when asymptotic freedom is lost. Additionally, we prove that our analysis is connected to the Gaussian fixed point as our results nicely match with the perturbative beta function. Intriguingly, we observe that it is hard to achieve large values of the renormalized coupling on the lattice. This might be an early sign of the existence of a physical cutoff and imply that a larger number of flavors is needed to achieve the safe fixed point. A more conservative interpretation of the results is that the current lattice action is unable to explore the deep ultraviolet region where safety might emerge. Our work constitutes an essential step toward determining the ultraviolet fate of nonasymptotically free gauge theories.Peer reviewe

Gradient flow running coupling in SU(2) gauge theory with N-f=8 fundamental flavors

We study the evolution of the coupling in SU(2) gauge field theory with N-f = 8 fundamental fermion flavors on the lattice. This model is expected to have an infrared fixed point at high coupling. We use HEX-smeared Wilson-clover action, and measure the gradient flow running coupling with Dirichlet boundary conditions. Extrapolating our results to continuum, we find an infrared fixed point at g(*)(2) = 8.24(59)(-1.64)(+0.97), with statistical and systematic error estimates. We also measure the anomalous dimension of the quark mass operator, and find its value at the fixed point. gamma(*) similar or equal to 0.15 +/- 0.02, although for this quantity a reliable continuum limit is still lacking.Peer reviewe

Conformal window in SU(2) with fundamental fermions

We present the updated results of the infrared behavior of the SU(2) model with 6 and 8 fundamental representation fermions. We use the gradient flow method with the Schrödinger functional boundary conditions to measure the running of the coupling in these theories and find fixed points on both. We also measure the mass anomalous dimension from these configurations.Peer reviewe

Epidemiology of hepatitis B infection in Finland: Implications for immunisation policy

Objectives: We describe the current epidemiology of acute and chronic hepatitis B infections in Finland. We estimate the total incidence of chronic hepatitis B following from the current incidence of acute infections and the influx of chronic carriers of hepatitis B associated with net immigration. We evaluate the incidence of hepatitis B infections preventable by a universal vaccination programme among infants.Methods: We analysed hepatitis B cases reported to the National Infectious Disease Register during 2004-2012 and used pre-developed methods to adjust for acute asymptomatic infections. We estimated the projected incidence of chronic infection by applying age-specific risks of chronic infection to the estimated incidence of acute infection. We estimated the influx of chronic carriers associated with immigration by utilising data on immigration during 2004-2012 and the WHO regional estimates of carriage prevalence.Results: The estimated incidence of acute hepatitis B infection in Finland, adjusted for asymptomatic infections, was 1.67 per 100,000 per year (95% Crl 1.43-1.94) which is 4.2-fold to the register-based incidence. The estimated lifetime risks of acute and chronic hepatitis B infections were 0.13% and 0.01%, respectively. We estimated that annually seven new chronic infections would result from infections acquired in Finland. These new chronic infections accounted for 1.2% of the total incidence of chronic infections. We estimated that eventually three chronic infections per year would be potentially preventable by a universal infant vaccination programme.Conclusions: Partly due to the fact that hepatitis B infections in neonates and in children are rare, a very limited number of chronic hepatitis B infections resulted from infection acquired within the country. A vast majority of chronic hepatitis B infections occurred among foreign-born persons and were therefore not preventable by a universal infant immunisation programme in Finland. Even with a targeted immunisation programme, the incidence of hepatitis B infection has remained low. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license