Vaccine breakthrough: ’we need the numbers’

More data on Covid transmission should be released, writes UL student Frank Fitzgerald

’Is there any possibility that vaccine breakthrough is a good deal more common than we realise?’

’Is there any possibility that vaccine breakthrough is a good deal more common than we realise?’


The last week has been somewhat of a roller coaster. We have gone from a situation where it appeared the country had indeed at last come to suppress Covid-19, to one where the hospital system is again now under severe pressure.

No-one knows why this has happened - as it has all over Europe, in the UK, Germany. The health authorities’ best guess is that increased socialising has led to rapid transmission increases (in retrospect perhaps hardly surprising considering that’s what we’ve encouraged everyone to do since June). The problem is we’re still missing a key piece of the puzzle: is the widespread Covid transmission coming from vaccinated people?

We know that most hospitalised cases were unvaccinated (although those who are immunocompromised should not be forgotten - when infections go up even the most vaccinated vulnerable citizens are at risk). What we do not know - either because the data has not been collected or is not being released - is what percentage of total cases are vaccinated. The assumption currently is that it is merely the unvaccinated who are driving transmission, but with 90 per cent of the population aged 16+ vaccinated is this certain?


According to CSO data, from September 17th (roughly by which time we had near-total vaccine uptake in the over-16 population) to October 15th, no more than 13 per cent of the 65+ cohort were reported in the case numbers in any one week, a small blessing amongst everything.

Between 22-34 per cent of the cases were in the 0-14 category over that period of time. However, that leaves between 66 and 78 per cent of the cases in all other age brackets - all of which together are 90 per cent vaccinated.

The accepted wisdom at present is that the still-unvaccinated younger groups in June and July represented a transmission reservoir that allowed Covid-19 to continue circulating even as the disease prevalence in other age groups was pushed down by vaccination. However given the continued - and rising - transmission of the disease through not only this age group but the other adult cohorts as well (even after these groups together are supposed to have reached a protected status of 90 per cent) is there any possibility that vaccine breakthrough is a good deal more common than we realise?

As early as at least August we had first-hand indications from Israel and Public Health England studies that the vaccines, though effective in preventing hospitalisation, may not prevent symptomatic infection with the Delta variant. Perhaps we concentrated too much solely on tracking hospitalisations without adequately tracking symptomatic transmission by vaccinated people.

Vital tool

In the US the CDC stopped tracking asymptomatic infection amongst vaccinated people some time ago, so it isn’t exclusive to Ireland or Europe. However, as of this moment, especially in the last week, we are seeing a situation where growth is accelerating exponentially but where (apparently) we do not even know how frequently infection is occurring amongst the vaccinated. We therefore do not know what is driving the surge.

This is a practical issue - even moreso since nightclubs reopened. We are relying on vaccination status to minimise transmission in otherwise high-risk environments; yet we do not even know how likely it is that those who are vaccinated may be transmitting the disease, negating the utility of the vaccine pass alone. We need to know. If that is the case then it would surely call for a combination of vaccine passes and antigen tests; too often the debate is around having one or the other.

And it shouldn’t be that difficult - if we can ascertain the vaccination status of extremely-ill Covid patients in hospital then surely we can do the same when someone (otherwise perfectly healthy) tests positive.

Looking forward

In the long-term this could be one key component of our ability to predict future waning population immunity. If collective immunity against hospitalisation begins to wane can we really afford to wait until a spike appears in hospitalisations like we’ve seen in the last two weeks? When we see vaccinated people in hospital that is surely a double time-lag, the first being the two-week gestation cycle of the disease, and the second another 5-12-days after symptoms appear where the person’s condition may deteriorate, necessitating hospitalisation. To rely on tracking percentages of vaccinated people becoming hospitalised is surely to wait until the situation has spiralled out of control - and the next gestation cycle of new infections is just beginning.

In the last week we’ve seen the situation spin precipitously out of control seemingly without warning. If, God forbid, another variant appears with a genuine capacity to neutralise our vaccines then vaccine breakthrough will first appear as a rise in the number of fully vaccinated people becoming infected - days or weeks before a spike in hospitalisations. We can’t afford to go without this early warning metric.

Up to now the mantra has been to follow the data and trust the science. We shouldn’t forget this when it comes to vaccine breakthrough.

Frank Fitzgerald is a student of politics and public administration at the University of Limerick.