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Corona-confusion Covid-19 can’t be eliminated with current vaccine uptake, says Prof Cillian De Gascun

Yesterday, 2,180 coronavirus cases were confirmed in the State - the highest daily case figure since January. This is despite 88pc of the population aged over 12 being fully vaccinated

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The current rate of Covid-19 vaccine uptake along with the effectiveness of the vaccines isn’t currently enough to suppress the virus alone, according to a leading virologist.

However, Professor Cillian De Gascun, director of the UCD National Virus Reference Laboratory and a member of the National Public Health Emergency Team (Nphet), stressed that this does not mean the vaccines are not effective.

Yesterday, 2,180 coronavirus cases were confirmed in the State - the highest daily case figure since January. This is despite 88pc of the population aged over 12 being fully vaccinated.

With much of the public querying why case numbers are so high with a high rate of vaccination, Prof De Gascun explained that the current vaccination uptake alone isn’t enough to suppress or eliminate the virus.

In a thread on Twitter, the virologist explained that in order for a virus to be brought under control, the percentage of the population vaccinated multiplied by the effectiveness of the Covid-19 vaccines must be greater than the percentage that is needed for herd immunity.

Instead of the phrase ‘herd immunity’ however, he used the term ‘community level protection’ (CLPT). He said this percentage can be derived from the reproductive number (RO) of the virus.

“We have an RO of 5-8, a CLPT of 80-88pc, a VE [vaccine efficacy] of 75pc (range 53-91pc, per SY Tartof et al, Lancet 2021), and vaccine uptake of 88pc in those more than 12 years of age,” he said.

“However, this level of vaccine uptake – when measured across the entire population – equates to somewhere between 75pc and 80pc. On that basis, and taking into account the cohort of the population that is not (yet, at least) eligible for vaccination, we can see that the current first generation of #SARSCoV2 vaccines is unlikely – in isolation at least, i.e. without additional public health measures – to be able to control #SARSCoV2 Delta in the community.

“So, to simplify the above, vaccine uptake rate multiplied by vaccine effectiveness should be greater than the CLPT for a virus to be brought under control.”

Prof De Gascun added that taking all this into account, the threshold to suppress Covid-19 within the community has not been reached with the current vaccines.

"As a result, we will continue to see case numbers increase as restrictions ease,” he said.

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"This does not, and I stress, does not, mean that the #SARSCoV2 vaccines are not effective.

“It simply means that they are not sufficiently effective – on their own – to suppress or eliminate #SARSCoV2 transmission in the community. However, they are very effective at protecting against hospitalisation and severe disease.”

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