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Bermuda would need 87.5% herd immunity if Delta variant takes hold

On the front line: government scientist Carika Weldon (File photograph by Blaire Simmons)

More than 87 per cent of the population would need to be vaccinated in order to achieve herd immunity from Covid-19 variants, according to a government scientist.

Carika Weldon made the recommendation in an affidavit last month after a number of positive test results showed that the Delta variant of the virus was on the island.

The Government has previously maintained that 70 per cent of the population need to be vaccinated to reach herd immunity.

According to the latest figures released last Tuesday, 63.2 per cent of the population has had two doses of the vaccine while a further 1.7 per cent has had one shot.

In her affidavit, Dr Weldon, who runs the Government’s Molecular Diagnostic Laboratory, explained that the herd immunity level would need to be raised to 87.5 per cent if the more contagious Delta variant got a foothold in Bermuda.

She said: “Testing since June 3, 2021 has shown that the majority of cases are either Beta or Delta strains. This is a shift from earlier months where a majority of cases were Alpha.”

Dr Weldon said that, up to June 28, there had been seven cases of the Beta variant recorded on the island, seven cases of Delta, and just one of the normal variant. The strain of a further four positive cases was undetermined.

Dr Weldon explained that a greater number of people needed to be vaccinated if a variant of the virus was more contagious.

She said: “The December 2020 outbreak was all normal strains but saw active cases rise from 20 to just under 300 in a matter of weeks.

“The introduction of a more transmissible virus (B.1.1.7.) saw this trend triple up to over 900 cases in March-May 2021.”

Dr Weldon provided a list of the different strains of the virus, along with the recommended percentage of the population that had to be vaccinated to provide herd immunity against each strain.

She said that 60 per cent of the population needed to be vaccinated to provide herd immunity against the original strain of the disease.

But this figure rose to 80 per cent for the Alpha variant — and 87.5 per cent for the Delta variant.

Dr Weldon said: “As a result, and given the presence of variants on the island, or the potential for variants to spread, Bermuda has not had a sufficient percentage of the population vaccinated to establish herd immunity.”

Kim Wilson, the Minister of Health, said at the Government’s Covid-19 press conference tonight that 92 per cent of the most recent 13 cases imported to the island were the Delta variant, while 8 per cent were the alpha variant.

Asked yesterday if the Government would review its community immunity goal of 70 per cent in light of the more dangerous variant’s arrival in Bermuda Ms Wilson said: “We are constantly reviewing our data and best practices internationally.

“When decisions are made, they will be communicated accordingly.”

A government lawyer has suggested that the figure could be changed.

Delroy Duncan spoke out during last week’s Supreme Court hearing in which public safety orders were challenged for being unconstitutional.

In a discussion of Dr Weldon’s testimony, Chief Justice Narinder Hargun asked if, in light of the Delta variant now on the island, the 70 per cent vaccination target still stood.

Mr Duncan replied: “I think it may be subject to review now.”

In her affidavit, Dr Weldon praised the health service for coping well with the virus, but warned that outbreaks could put pressure on the system.

She said: “A small island like Bermuda is vulnerable to undetected cases of the virus, especially those of more transmissible variants.

“Due to our size, effects are amplified compared to larger countries such as the US or UK.

“The public health system in place to respond to Covid-19 is very good, but relies solely on frontline workers working daily due to daily incoming flights.

“When this is further stressed by an outbreak, it becomes impossible to sustain as there [is] worker fatigue, the workforce diminished due to quarantine [as Bermuda is so small and a case is not so far removed] and ultimately can lead to errors.”

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Published July 14, 2021 at 8:06 am (Updated July 14, 2021 at 8:06 am)

Bermuda would need 87.5% herd immunity if Delta variant takes hold

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