THE HIGHER TRANSMISSION rate of the Delta variant means Covid-19 could do “very significant damage” in Ireland’s partially vaccinated population if indoor hospitality is reopened, according to Professor Philip Nolan. 

The chair of the Irish Epidemiological Modelling Advisory Group said it has been a “difficult and disappointing week for many” as the threat of the Delta variant prompted the government to halt Ireland’s reopening plans.

However, Professor Nolan, who provides statistical support to the National Public Health Emergency Team (NPHET), described the likely impact of the variant as “stark” and noted that “caution is well advised”. 

Nolan shared the group’s data in a series of posts on Twitter, explaining that it uses scenario models to “help NPHET and the government think quantitatively about risks and likely disease trajectories and impacts”.

He said that last summer’s reopening led to the reproduction number of the virus increasing from below one to between 1.4 and 1.6 

“However, because the level of infection in late June 2020 was very low, it was weeks before the underlying exponential growth became apparent; essentially the seeds of the October 2020 surge were sown in July and August 2020,” he explained.

UK researchers estimate that alpha is 40-90% more transmissible than antecedents, and delta 40-60% more transmissible than alpha https://t.co/Pk5qn29AFK https://t.co/g1e7uD1Gel 14/36

— Professor Philip Nolan (@President_MU) June 30, 2021

Prof Nolan cited research from the European Centre for Disease Prevention and Control in noting that the Delta variant is far more transmissible than the strain that was in circulation last summer.

“So the same levels of social mixing will lead to much higher levels of transmission and much faster growth in cases, which will be attenuated by progressive vaccination,” he said.

Even the most optimistic scenario with the Delta variant shows opening on July 5th risks a significant surge in cases; note that case numbers rise very slowly through July and then surge in August and September, this being the nature of exponential growth.

Prof Nolan said that a rise in new cases will “inevitably lead to hospitalisation and mortality, though the rates will be far less than we experienced without vaccination; nonetheless, a long wave of disease leads to a significant number of adverse outcomes”.

The model indicated that 99% of the potential deaths that would occur would be in those over 40.

“Why would this happen if everyone is vaccinated? Vaccines offer extraordinary protection, but not perfect,” he said.

We have almost 500,000 people aged 70 and over. Even if the vaccine is 95% effective in preventing severe disease, 25,000 people remain vulnerable.

Prof Nolan said the Delta variant’s transmission advantage could enable it to do “very significant damage” if it was allowed to spread in Ireland’s partially vaccinated population.

“The scale of the damage depends on the transmission advantage, and it starts slowly and escalates rapidly,” he explained. 

Virologist Dr Kim Roberts told The Journal that research has found that people who are partially vaccinated are around 75% protected from being hospitalised due to Covid-19.

Because only approximately 42% of the eligible population are fully vaccinated, a lot of people are still at risk of suffering a severe dose of the illness.

Dr Roberts explained that there is a broad range of symptom severity, even after vaccination, and people who have been partially or in some cases fully vaccinated, can transmit Delta variant on to others.

“Unfortunately, some people who are most at risk of severe Covid-19, due to other health issues, may still be at risk even after vaccination because some people won’t develop a strong immune response to the vaccine,” the Trinity College Dublin assistant professor said.   

“All of this taken together means that if transmission of the Delta variant is allowed to rise, due to further transmission restrictions being removed, such as indoor dining restrictions, then we will see not only a rise in infections but also a rise in the number of people needing hospital care and the subsequent rise in deaths,” she added.