Omicron will be a very significant challenge, but we are acting early, quickly and comprehensively. If we take a booster vaccine when offered, significantly limit contacts, mitigate risk, self-isolate if symptomatic and restrict movements if a contact, we can get through it. 1/22 The purpose of the formal restrictions is to significantly reduce risky social contact, the opportunity for the virus to transmit; they are to reinforce a call to all of us to prioritise our socializing over the coming weeks to a small group of people who matter most to us. 2/22

Let’s think and act positively. We can, with collective action, control transmission of SARS-CoV-2 again, and relieve the pressure of COVID-19 on our healthcare system. The effective reproduction number is currently estimated at around 1.2 1/12 If we can reduce our close social contacts by 30%, and/or mitigate the risks of those social contacts by 30%, we will have done enough to see the level of infection, case numbers and ultimately hospitalisations decline. 2/12

The latest modelling of SARS-CoV-2 infection in Ireland shows that we urgently need to reduce transmission if we are to avoid further dangerous increases in cases and hospitalisations. Stay home with symptoms, limit contacts, use basic mitigations. 1/20 The current surge in disease began soon after the relaxation of measures on 20 Sept 2021, and accelerated from 22 Oct 2021 through the mid-term break. The increase in effective social contact is the primary driver, along with waning vaccine immunity. 2/20

Why are SARS-Cov-2 infections increasing in Ireland? It’s complex, but most likely a mix of increased mobility and social contact since late September, slippage on transmission prevention measures, and more social mixing indoors. 1/16 We had high but stable levels of infection through September 2021, but this was created by a very dynamic and delicate balance between increasing vaccine protection suppressing the virus, and increasing social contact creating opportunities for the virus to spread. 2/16

There is no evidence that the reopening of schools has led to an increase in transmission or levels of infection amongst school-going children or more widely across the population. 1/14 The level of infection in children and adolescents had increased in the course of the summer as the delta variant increased the rate of transmission. 2/14

A lot of commentary saying that most or all schoolchildren will be infected with SARS-CoV-2 in the coming months, based on an uncritical reading of this modelling study. It is highly unlikely that the scenario modelled will happen in the real world. 1/12

medrxiv.org/content/10.110… First, it’s not plausible. In the 12 weeks after primary schools reopened in March 2021 we detected 5,279 cases in children aged 5-12 years, or just under 1% of the population. The vast majority of these infections were transmitted in the community, not in school. 2/12

A clear and balanced interview from public health doctor Dr. Abigail Collins. Her leadership has been critical to making the reopening of schools as safe as possible. The analysis and first-hand experience she reports is supported by the national data 1/4
rte.ie/radio/radio1/c… There was a marked increase in testing of children as schools reopen, but the percentage positive fell rapidly. Incidence in children, which had risen to very high levels during July, stabilised in August as the force of infection from the adult population decreased. 2/4

A note of appreciation to the principals, teachers, staff, administrators, public health doctors, parents and students who have worked hard to make our schools as safe as possible and are looking forward to a full return to in-person schooling. 1/15 There is considerable evidence that, with effective mitigation measures in place, schools are not major sites of transmission, and this is affirmed by the experience of public health doctors who supported the safe opening of schools in Spring 2021. 2/15
hse.ie/eng/services/n…

#VaccinesWork. We have seen extraordinary uptake of vaccination in Ireland, and this is making us safer, but we need to give the vaccines time to work. The message: get your vaccine, get your second dose, and wait the 7-14 days they need to build your immunity. 1/7 Yes, over 90% of adults have had their first dose, and over 80% have completed their vaccination regimen, but only about 75% of adults are two weeks after their final dose; 25% of the adult population not yet fully vaccinated is enough for a large wave of disease. 2/7

We have breached 2000 cases per day, 2074 cases today, the first time we have had more than 2000 cases since 21 January. We have had more than 2000 cases on only 21 of the 532 days since we reported the first case here. 1/9 This is very different from January. Vaccination is preventing an enormous number of transmissions, and is reducing the severity of disease in the minority who become infected despite vaccination. Nonetheless, the rising incidence is a real concern. 2/9

#VaccinesWork. The increasing proportion of cases and hospitalisations in fully vaccinated people is in line with expectations, and tells us vaccines are working, are highly effective, and are preventing a very large number of infections and hospitalisations. 1/6 We have adapted the very elegant @jburnmurdoch visualization to the current situation here. We have 70% of the adult population protected (two weeks after completing their regimen) and would expect about 30% of cases and 15% of hospitalisations to be fully vaccinated. 2/6

Case numbers may appear to be plateauing, but are probably not, just growing more slowly than a week ago. If growth rate is slowing, it’s because of our collective caution, and is a signal to keep up the basic public health precautions, not let down our guard. 1/13 We have had an unusual pattern of infection over the last five weeks, with the return of exponential growth in late June, superimposed on which was a step change in cases in mid-July, and now cases seem to be growing from this higher level 2/13

Case numbers continue to rise. This will translate into an as-yet-unknown level of severe disease and mortality over the next 2-4 weeks. We know from models and international data that it will be much less than before vaccination, but it remains uncertain and dangerous 1/7 The rate of growth is very concerning, about 6% per day; if this continues case numbers will double every 12 days, building up a very large force of infection and burden of disease. We need to be exceptionally careful in the coming weeks. 2/7

Ventilation is important, but other factors are equally or more important. SARS-CoV-2 transmits in droplets, fomites (particles, objects and surfaces) and aerosols. We do not know for certain the relative importance of each, so let’s be careful about all of them. 1/8 The best available evidence, and the experience of public health doctors managing outbreaks, strongly suggest that the majority of transmissions occur with close contact, close enough for droplets, and aerosols in high concentration, to transmit the infection. 2/8

The data are saying one thing: be very cautious faced with the delta variant. We are seeing a very steep rise in cases, comparable to or steeper than the early part of previous waves. 1/9 This will not translate into severe disease and mortality in the same way as before, but numbers in hospital are rising: 101 this morning. The ratio of admissions to cases is 16 admissions per 1000 cases, overall we are tracking 15-25 admissions per 1000 cases. 2/9

It’s worrying to see incidence appear to increase after a long period of stability or slow decline, and especially concerning that it is increasing across almost all age groups. Daily average case count 387, up from 311 one week ago. 1/4 Incidence is increasing across all age groups from 5 to 70 years of age, notably in those age cohorts where there are significant numbers of partially vaccinated people, a reminder of the importance of that second dose, and that delta exploits the vulnerability between doses. 2/4

It has been a difficult and disappointing week for many, as the rise to dominance of the delta variant has delayed plans for wider reopening; but the likely impact of delta is stark, and caution is well advised. 1/36 We use scenario models to help NPHET and Government think quantitatively about risks and likely disease trajectories and impacts. The short form: we use a number of standard models, they are already published, and the effect of vaccination is included. 2/36

Dr. Mina, you have inferred a great deal about my knowledge and motivation from one tweet; fair enough, it may not have been my finest moment in pandemic communications. Nonetheless, a few points of clarification and response. 1/15

https://twitter.com/michaelmina_lab/status/1391228033500160003

First, there is a context. This is not about antigen testing in general, which does have and will continue to have a role in our management of the pandemic. 2/15

A lot of reasons to be optimistic. While incidence is relatively high, it is stable, due to our collective efforts to minimize transmission. If we remain careful, and keep each other safe, we can see this through the few weeks until vaccination offers us greater protection. 1/4 Incidence has remained stable through April, and test positivity below 3% despite intense testing. The numbers in hospital and ICU are decreasing; importantly, daily admissions remain low. 2/4

We have looked carefully at incidence of SARS-CoV-2 infection in children in recent weeks for any impact of the phased return to the classroom. The data, and thorough public health investigation, confirm that schools remain a low-risk environment. 1/16 Schools are low risk because of the mitigation and protection measures put in place by teachers, principals, families, general practitioners and public health doctors. 2/16

Let’s protect the vulnerable. Keep your contacts to a minimum between now and Christmas and then celebrate with a small circle. Meet outdoors if you can. If indoors: limit numbers and duration, use masks and keep your distance, gentle natural ventilation. 1/5 It’s good that numbers in hospital and ICU are falling. Behind each number is a human story of illness and loss. Hospitalisations lag behind cases, and sadly what we are seeing now is the impact on older and vulnerable people infected towards the end of the recent surge. 2/5