THE DELTA VARIANT will “almost certainly” be the dominant strain of Covid-19 in Ireland by mid-July, leading to an increase in case numbers, hospitalisations and deaths, according to virologist Dr Cillian de Gascun.

The director of the National Virus Reference Laboratory said the available evidence suggests the Delta variant is between 40% and 60% more transmissible than the Alpha strain of the coronavirus, which has been dominant in Ireland for the last five months.

In a series of posts on Twitter, De Gascun, who is a member of the National Public Health Emergency Team (NPHET), said the Delta variant has an increased growth rate, an increased secondary attack rate and increased household transmission compared to the Alpha variant.

He added that there is also laboratory evidence of increased replication in biological systems that model the human airway.

“Because the Alpha variant was itself significantly more transmissible than the original SARS-CoV-2 virus, we can say that Delta is almost certainly at least twice as transmissible as the virus we experienced last summer,” De Gascun said.

He added that data from England and Scotland suggests that infection with the Delta variant roughly doubles the risk of hospitalisation, compared with the Alpha strain. 

The NPHET member noted that the case fatality rate for Delta, which stands at 0.3%, appears to be lower than for Alpha (2%) but a large number of cases are still within the follow-up period. “So we still have more to learn about the clinical course of disease with Delta infection,” he said.

He added that the variant does not appear to be associated with an increase in reinfections among people who previously recovered from the disease.

De Gascun noted that the variant is associated with a reduction in vaccine effectiveness, particularly after one dose. “Although this is concerning, vaccine effectiveness against Delta is high after two doses, and vaccine effectiveness  against hospitalisation is maintained,” he said.

Public Health England announced earlier this month that the Delta variant is the dominant strain in the UK. The European Centre for Disease Prevention and Control (ECDC) has also forecast that the variant will be responsible for 90% of infections in the European Union by the end of August.

The virologist said transmissibility data in Ireland suggests Delta will become dominant in a matter of weeks.

In Ireland, it’s likely Delta will become dominant much sooner than that. Based on S gene data from the Thermo Fisher assay, the proportion of cases due to Alpha in Ireland has declined from 91% in week 23 (beginning June 7th) to 45% in week 25 (beginning June 21st) 10/n

— Cillian De Gascun (@CillianDeGascun) June 29, 2021

“This dramatic increase in the proportion of Delta over the last two weeks will almost certainly lead to Delta dominance by the middle of July, with a consequent increase in case numbers, hospitalisations, and mortality in the following weeks,” he said.

De Gascun noted that a significant difference between now and last summer is that very effective vaccines are now available.

He urged people to protect each other – by maintaining social distancing, wearing masks, managing their number of contacts and practicing hand hygiene – while the vaccines take effect.

The latest vaccine statistics reveal that more than 4.1 million doses have been administered in Ireland. As of Tuesday night, close to 2.5 million people have received at least one dose (64% of the eligible population) and more than 1.67 million people have two doses (42% of the eligible population).