COVID-19: What if immunity wanes?

Using a simple economic model in which social distancing reduces contagion, we study the implications of waning immunity for the epidemiological dynamics and social activity. If immunity wanes, we find that COVID-19 likely becomes endemic and that social distancing is here to stay until the discovery of a vaccine or cure. But waning immunity does not necessarily change optimal actions on the onset of the pandemic. Decentralized equilibria are virtually independent of waning immunity until close to peak infections. For centralized equilibria, the relevance of waning immunity decreases in the probability of finding a vaccine or cure, the costs of infection (e.g., infection-fatality rate), the degree of partial immunity and the presence of other NPIs that lower contagion (e.g., quarantining and mask use). In simulations calibrated to July 2020, our model suggests that waning immunity is virtually unimportant for centralized equilibria until at least 2021. This provides vital time for individuals and policy-makers to learn about immunity against SARS-CoV-2 before it becomes critical.

COVID­19 : et si l'immunité diminuait? À l'aide d'un modèle économique simple dans lequel la distanciation sociale permet de réduire la contagion, nous analysons les conséquences d'une baisse de l'immunité sur les dynamiques épidémiologiques et les activités sociales. Nous constatons que si l'immunité décline, c'est que la COVID­19 devient vraisemblablement endémique et que la distanciation sociale est vouée à perdurer jusqu'à la découverte d'un remède ou d'un vaccin. Néanmoins, une diminution de l'immunité ne modifie pas nécessairement les mesures optimales à prendre dès le début de la pandémie. Les équilibres décentralisés sont théoriquement indépendants d'une baisse de l'immunité jusqu'à l'approche du pic d'infection. Pour les équilibres centralisés, l'importance d'une diminution de l'immunité décroît avec la probabilité de trouver un vaccin ou un remède, avec les coûts imputables à l'infection (par exemple le taux de létalité), avec le taux d'immunité partielle et en présence d'autres interventions non pharmaceutiques (INP) permettant de diminuer la contagion (mises en quarantaine et utilisation du masque notamment). Dans les simulations calibrées sur juillet 2020, notre modèle montre qu'une baisse de l'immunité est pratiquement sans importance sur les équilibres centralisés, et ce au moins jusqu'en 2021. Cette période cruciale permettra aux individus et aux législateurs d'en apprendre davantage sur l'immunité contre le SARS­CoV­2 avant que le virus ne devienne critique.

Comparative evaluation of clinical efficiency of intramuscular diazepam-ketamine, medetomidine-ketamine, and xylazine-ketamine anaesthesia in Ring-necked pheasants (Phasianus colchicus).

BACKGROUND: Several injectable anaesthetics and sedatives are used in various avian species for general anaesthesia. Birds are very sensitive animals and any mismanagement in a crisis can lead to immediate shock and death. Therefore, careful selection of the safest possible anaesthetic agent and dose is very important. AIMS: The aim of this study was to examine the clinical efficiency of diazepam-ketamine (DK), medetomidine-ketamine (MK), and xylazine-ketamine (XK) combinations anaesthetic regimens in pheasants. METHODS: Twenty-four pheasants were divided into three equal groups and received one of three anaesthetic combinations by intramuscular injections: 9.0 mg/kg diazepam and 150.0 mg/kg ketamine, 0.20 mg/kg medetomidine and 80.0 mg/kg ketamine, and 3.0 mg/kg xylazine and 80.0 mg/kg ketamine. Each pheasant was pre-medicated with sedative drugs and 5 min later, anaesthesia was induced with ketamine injection. RESULTS: The weak time (2.50 ± 1.07 min; mean±SD) and down time (6.13 ± 1.25 min) were shortest in group XK. The sleep time was longest (73 ± 20.24 min) while the recovery time (157 ± 13.61 min) was shortest in group MK. Muscle relaxation was excellent during the anaesthesia in all groups. The recovery phase of the birds was uneventful. Heart rate (HR) in DK group was statistically higher than MK and XK groups. Body temperature (BT) decreased in all groups compared to baseline values and those of MK group were lower than DK and XK groups. Respiratory rate (RR) in XK group was significantly lower than DK and MK groups. CONCLUSION: In conclusion, the MK combination shows better anaesthetic outcome compared to DK or XK combinations in pheasants.

Effects of short-term high carbohydrate or fat intakes on leptin, growth hormone and luteinizing hormone secretions in prepubertal fat-tailed Tuj lambs.

The aim of the current study was to evaluate the effects of high carbohydrate or fat diets, fed for 15 days at the end of breeding season, on leptin, GH and LH secretions in prepubertal fat-tailed Tuj lambs. For that purpose, 9-month-old ram-lambs were divided into three groups as control group (fed with basal ration, n = 4), high carbohydrate (HC) group, basal ration plus barley, n = 4), or high fat (HF) group (basal ration plus by-pass fat, n = 4). For the measurement of leptin and GH, blood plasma samples were collected on days 1, 4, 9 and 14 of the experiment. For the measurement of LH pulse frequency, serial blood samples were collected every 15 min for 6 h on day 14. Lambs were weighed and body condition scored (BCS) on days 1 and 15. Body weight and BCS increased towards the end of the study (p < 0.05). The BCS was higher in high energy groups at the end of the experiment (p < 0.05). Diet affected plasma leptin concentrations (p = 0.002) but time did not. The GH concentrations were not affected by diet or time. The LH pulse frequency appeared to be higher in HC and HF groups but there were no statistical difference between the groups. There was a significant positive relationship between overall BCS and corresponding leptin concentrations (R2 = 0.263; p = 0.010) and between LH pulse frequency and leptin concentrations (R2 = 0.594; p = 0.003). In conclusion, the present study suggests that rather than type of energy, amount of energy intake and body energy reserves are much important regulators of plasma leptin concentrations and LH pulse frequency in fat-tailed Tuj lambs.

Effect of medetomidine-butorphanol-ketamine anaesthesia and atipamezole on heart and respiratory rate and cloacal temperature of domestic pigeons.

The purpose of this study was to evaluate the sedative-anaesthetic effects of a combination of medetomidine (M, 50 microg per pigeon), butorphanol (B, 50 microg per pigeon) and ketamine (K, 25 mg per pigeon) in domestic pigeons. Eight domestic pigeons (four male and four female, 8-15 months old) were used. The combination of Medetomidine and butorphanol injectable solutions were used to produce sedation. Ten minutes after M + B administration, K was injected. The anaesthetic effects of the drugs were reversed by administration of Atipamazole (AT) at 60 min after K administration. All drugs were injected into the pectoral muscles. The sedative-anaesthetic effects of the M + B-K combination and, alterations in respiratory rate (RR), heart rate (HR), electrocardiographic (ECG) findings and cloacal temperature (CT) were investigated before and 10 min after pre-medication with M + B, at 5, 15, 30, 45 and 60 min during the onset of K anaesthesia and at 1, 5, 10, 20, 30 and 60 min following the administration of AT. The HR and RR of pigeons decreased within 10 min following M + B administration and remained lower until 1st and 5 min of AT injection, respectively. In ECG, no significant alterations in P, Q, R and S-values were observed, however, arhythmia was recorded for three pigeons, which returned to normal values following AT administration throughout the measurement. Cloacal temperature decreased gradually during the anaesthesia from 41.0 to 32.7 degrees C. The drug combination used in this study produced a satisfactory general anaesthesia for seven of the eight pigeons. All pigeons were unconscious within 5 min after K administration as indicated by disappearance of the palpebral and corneal reflexes and lack of reaction to the pain stimuli during the study. The effect of AT administration was observed within 10 min as all pigeons responded partly against stimuli and all reflexes. It is concluded that M + B-K anaesthesia in pigeons is a safe and reliable anaesthetic protocol for surgery.