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20/10/2021

Health chief in warning over Delta variant vaccine protection

Health chief in warning over Delta variant vaccine protection

Health chief in warning over Delta variant vaccine protection

Dr Cillian de Gascun, the director of the National Virus Reference Laboratory, has given an update on the Delta variant of Covid-19 which he expects to the dominant strain in Ireland by the middle of July.

He outlined the reasons why he and his fellow health chiefs are concerned.

"As any new variant emerges, there are three main issues that we consider: transmissibility; infection severity; and impact on pre-existing immunity (reinfection risk) and vaccine effectiveness.

"Firstly, based on available evidence, the Delta variant appears to be between 40% and 60% more transmissible than the Alpha variant, which has been dominant in Ireland for the last five months.

"When compared with Alpha, Delta exhibits an increased growth rate, an increased secondary attack rate, increased household transmission, and laboratory evidence of increased replication in biological systems that model the human airway.

"As such, 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," Dr De Gascun continued.

"Secondly, if we look at infection severity, data from Scotland and England show an increased risk of hospitalisation among individuals infected with the Delta variant compared to Alpha. Infection with Delta roughly doubled the risk of hospitalisation.

"The case-fatality rate for Delta (0.3%) at this time appears to be lower than that for Alpha (2%). However, 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.

"Thirdly, looking at immunity, neutralisation studies using convalescent sera show a reduction in neutralisation against Delta. However, this does not (yet at least) appear to be associated with an increase in reinfections among recovered individuals.

"However, we do see a reduction in vaccine effectiveness (VE) for Delta compared with Alpha against symptomatic infection, particularly after one dose. Although this is concerning, VE against Delta is high after two doses, and VE against hospitalisation is maintained.

"In the UK, Delta is the dominant variant, accounting for approximately 97% of cases. As a consequence, case numbers, hospitalisations, and deaths have increased in recent weeks. ECDC also predicts that Delta will be responsible for 90% of EU/EEA infections by the end of August.

"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).

"Alpha cases yield S gene negative results on this assay; Delta cases yield S gene-positive results. Based on the transmissibility data described earlier, it is probable that the vast majority of our S gene positive cases (i.e. 55%) are Delta. This will be confirmed by WGS.

"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.

"However, in contrast to last summer, we now have very effective vaccines. The key is to protect each other through established public health interventions (hand hygiene, distancing, mask-wearing, managing number of contacts) while the vaccines take effect."

He concluded: "Please remember that you are not fully vaccinated until two weeks after your second dose of ChAdOx1 Astra Zeneca vaccine, or 7 days after your second dose of Pfizer/BioNTech vaccine. Two doses are required for optimal protection against the Delta variant.

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