Current Covid-19 situation is complex and future is hard to divine

In advance of the National Public Health Emergency Team (Nphet) deciding on Monday on a response to the latest surge in Covid-19 cases, its members have been trying to explain what is going on.

Despite having the highest vaccination rate in Europe, Ireland has one of the highest incidences of Covid-19. Worryingly, it is rising again.

To take a local example, Waterford has the highest vaccination rate in the State, at 99.9 per cent, yet it also has the highest incidence of any county.

None of this means that vaccines are not effective, as Prof Cillian de Gascun, director of the National Virus Reference Laboratory, pointed out at the weekend. (Though it clearly shows they are not completely effective.)

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Prof de Gascun explained the current vaccination uptake is not enough on its own to suppress or eliminate the virus.

He highlighted the areas of weakness. We have 88 per cent of over-12s vaccinated, but that translates to only 75-80 per cent of the overall population.

Then, there is the effectiveness of the vaccine, which he estimates at no more than 75 per cent.

Reproduction number

Against this, the delta variant has an estimated reproduction number of between five and eight, meaning on average one case will pass the virus on to between five and eight others.

To end the pandemic, we need to ensure sufficient people are protected against the virus, either through natural or vaccine-induced immunity. This proportion of the population is necessarily higher because this variant is so transmissible.

Prof de Gascun reckons we need to reach a community-level protection threshold – a term he prefers over “herd immunity” – of 80-88 per cent in order to be able to eliminate the virus.

His assessment is that we are unlikely to reach this threshold using the current first generation of vaccines alone – that is, without additional measures.

Smallpox and measles have been eradicated or eliminated here, he notes, because this threshold has been reached. In contrast, mumps is still a scourge, largely because of the reduced effectiveness of the mumps component of the MMR vaccine.

But why are other European countries faring better than us at present? Rates in much of continental Europe and Scandinavia are a fraction of Ireland’s.

"We started at a disadvantage compared to most of western Europe," another Nphet member, Prof Philip Nolan, contended in a weekend Twitter thread. "We were hit by a very large wave of delta infections in July, with most of the population under 50 not yet vaccinated, driving daily cases from 300 to 1,800 per day between June and August."

At the start of July, Ireland had the same incidence as Sweden – maskless Sweden – but today our rate is six times higher.

For a time, that didn’t matter too much, as most of the cases were among younger people, and mild. Even the return to school was weathered, with cases among young children rising, and then falling again, in line with predictions.

But then older, more vulnerable people were infected, resulting in more hospital admissions – 60 per cent of ICU patients at present are over 65.

Proximity to UK

It still isn't clear why our figures are so bad relative to other countries. Minister for Health Stephen Donnelly has pointed the finger at our proximity to the UK, and the graphs for cases for the two countries over the last six months are similar.

One theory is that mildly infected children are bringing the virus home in greater numbers, now that routine contact tracing in schools has ended. Others emphasise the waning effectiveness of vaccines – though this would surely impact on our European neighbours as well.

Prof Nolan believes the increase in cases is most likely due to a mix of increased mobility and social contact since late September, slippage on transmission prevention measures, and more social mixing indoors.

Even allowing for the first and third points here being essentially the same, other countries have gone down the same road without the same outcome. Denmark, for instance, completely removed restrictions over a month ago, and does not seem too bothered about the subsequent rise in cases.

One difference between Ireland and some of the more successful countries in Europe is the minimal role assigned to rapid antigen testing here. On the other hand, the UK has spent three times more than any other country on antigen testing, and it has the worst Covid figures in Europe.

The situation is complex, and the future hard to divine. It was easier to predict trends earlier in the pandemic, but there are more moving parts to the equation than before. It is perfectly possible to suffer outbreaks and surges that affect particular groups (such as the unvaccinated) and areas, while the rest of society continues relatively unaltered. We may have to get used to that situation.