As the clocks have changed and we enter the darker winter months, a high level of immunisation against Sars-CoV-2 was expected to be our ticket to a more “normal” life. However, with Covid-19 hospitalisation levels rising and ICU beds filling up, do we need to reassess our confidence in the jab against the novel coronavirus?
A national adult immunisation rate in excess of 90 per cent is an incredible public health achievement for the Republic – one that few other states have been able to achieve. For many viral illnesses, a vaccine coverage rate of this magnitude would pave the way to control and even eradication of disease.
But with daily infections regularly exceeding 2,000 cases and 67 deaths with Covid-19 reported in the last week, we face a new reality. Latest statistics from the Economic Social and Research Institute (ESRI) show the number of locations that people are visiting on average has almost doubled since January, while the number of people who said they always wear masks, socially distance and hand-wash has fallen from more than 60 per cent to 40 per cent. One in five said they “rarely or ever” wore a mask or socially distance.
Hospital Report
Uncertain
At the latest Nphet media briefing on Covid-19, the deputy chief medical officer Dr Ronan Glynn, said the future trajectory of the disease was "very uncertain". Cases were rising at between 1-3 per cent per day, he said.
"It's not going to turn on vaccination alone. Clearly, vaccination alone is not going to be enough to turn around transmission," chief medical officer Dr Tony Holohan told the weekly briefing.
This is a key point as some doubt about vaccine effectiveness creeps in. Vaccines offer two distinct benefits: reducing severe disease and preventing viral transmission. Becoming infected, but with a mild version of the disease is a more likely outcome from vaccination. Preventing transmission of a circulating virus, while the ultimate silver bullet, is less certain.
We have seen this with the annual influenza vaccination, where vaccine effectiveness (VE) trials show that flu vaccination reduces the risk of flu illness by between 40 per cent and 60 per cent. A 2018 study showed that among adults hospitalised with flu, vaccinated patients were 59 per cent less likely to be admitted to the ICU than those who had not been vaccinated – a clear illustration of the disease-ameliorating effect of flu vaccination.
Vaccines remain highly effective at preventing severe disease and deaths from Covid-19, but some studies suggest they may be less effective against the Delta variant – currently the dominant strain worldwide – though the reason for this has not yet been established.
Risk of infection
However, a study of 621 people in the UK with mild Covid-19 infections, published in The Lancet Infectious Diseases, found that people who received two vaccine doses could still pass the infection on to vaccinated and unvaccinated household members.
Infections in vaccinated people cleared more quickly than those in unvaccinated people, but resulted in a similar peak viral load – when people are most infectious – probably explaining why the Delta variant remains able to spread despite vaccination.
The results also suggest that the risk of infection increased within three months of receiving a second vaccine shot, and is likely due to waning protective immunity, the authors say. Although vaccines remain highly effective at preventing severe disease and deaths from Covid-19, the findings suggest that vaccination is not sufficient to prevent transmission of the Delta variant in household settings with prolonged exposures.
This must not fuel an anti-vaccine agenda. Without Covid vaccines we would be looking at the complete collapse of our health service this winter. But the emerging message from the latest Covid-19 infection trends is unequivocal: continued public health and social measures to curb transmission – such as mask wearing and social distancing – remain important. Even in vaccinated individuals.