How are COVID vaccines faring against Delta?

Anastasia Tsirtsakis

22/07/2021 3:52:38 PM

New insights from the UK and Israel suggest first generation vaccines may not be as effective, but it’s not all doom and gloom.

A laboratory technician examining a sample.
About 90% of new COVID cases in those aged over 50 in Israel have been fully vaccinated, according to a monitoring team at the Hebrew University.

Just as the world was hoping for a reprieve from lockdowns, soaring hospitalisation rates and deaths, the emergence of the Delta variant has seen new case numbers surge.
Since its detection in India, the strain, which is said to be 50% more transmissible than the Alpha variant of concern that previously dominated UK infections, has spread to at least 90 countries.
New research, published in The New England Journal of Medicine, has confirmed that both AstraZeneca and Pfizer COVID vaccines have a lower efficacy against Delta, with a single dose of either vaccine around 30% effective against the strain, compared to 48% for the Alpha variant.
However, after two doses, only modest differences were observed, with Pfizer 88% effective against Delta compared to 93% for Alpha, and AstraZeneca 67% effective against Delta and 74.5% for Alpha.
So how is this playing out in the UK?
With Delta now the dominant strain, case numbers have started to soar, with more than 330,000 people testing positive in the past seven days. Hospitalisation rates have also started to increase, with 4510 people admitted between 8–14 July, up 38.6% on the previous seven days, and 366 deaths recorded between 15–21 July, up 59.8% from the past week.
That is with 69.1% of the adult population fully vaccinated and 88.1% having received one dose.
But infectious diseases physician and microbiologist Associate Professor Paul Griffin told newsGP that the findings are not unexpected as Delta is more infectious, and that the reduced efficacy is ‘not all that significant’.
‘We know people that are fully vaccinated can still get infected,’ he said.
‘But what we also know is that they’re, at least modestly, reduced in terms of their ability to transmit, and have very significantly reduced chances of getting really sick, being hospitalised and dying.
‘And, again, that doesn’t mean that the numbers of deaths will go to zero. Even if we had 100% of people vaccinated, there’d still be one or two people per 100, and there’d still be 10 people that do get sick – but it’s significantly reduced.
‘We just have to look at the proportion that get really sick, and make sure that that doesn’t jump up indicating that our vaccines are no longer working. But we’re clearly not at that point yet.’
In Israel, where Delta is causing a fourth wave, health officials are less certain.
The country’s Ministry of Health earlier this month lowered its projection of Pfizer being 95.3% effective to just 64% against Delta, and warned that it could be even lower, as about 90% of new confirmed cases in those aged over 50 are fully vaccinated.
However, it is worth noting that while case numbers have risen from zero on 5 June to 668 on 19 July, deaths have remained low, with only two recorded on 19 July.
With 85% of adults vaccinated in Israel, Associate Professor Griffin says that in and of itself could be why the proportion of cases who are vaccinated appear to be overrepresented, but that more information is needed.

‘It’s hard to know what those case numbers would have been had they not had so many people vaccinated,’ he said.
‘So, it’s not really, at this stage, data that lends itself to concluding that the vaccine performs less well there.
‘I think part of it is a bit of a skewing of the numbers. The key thing there will be looking at, again, the serious cases, hospitalisations, and deaths. If they truly climb there would be concern about the actual efficacy being less than we think.’
Comparing Delta waves in countries with a high proportion of vaccinated adults to those with low vaccination rates, also suggests current vaccines are effective at reducing hospitalisations and deaths.

Likewise, the UK research, funded by Public Health England, has concluded the findings support efforts to maximise vaccine uptake with two doses among vulnerable populations.
As children appear to be more susceptible to the Delta variant, a number of countries have already approved COVID vaccination in children, including Israel, the US, France and Italy, with the UK set to offer vaccination to those aged 12–15 who are at higher risk of COVID due to disability or illness.
But Associate Professor Griffin believes even though there is a general consensus that children need to be considered that it is likely too early to do so in Australia, fearing it could contribute to coverage among adults remaining insufficient.
‘We still haven’t really got those younger adults [vaccinated], who are actually responsible for the bulk of transmission,’ he said.
‘They’re a really key group to get high rates of coverage in because that will reduce the ability for this virus to be transmitted in our community. Once all those people have had the opportunity to get the vaccine, then absolutely, as quick as we can, we should include children from there.’
As has been the case throughout the pandemic, what’s clear, is that Australia has a lot to observe from countries that have already vaccinated a large proportion of their population.
However, Associate Professor Griffin is wary of people’s interpretation of scenes unfolding in countries like England, where mandated mask use and social distancing ended just days ago.
‘It is interesting what they’ve done – and I can understand why they’ve made that decision. But we have to remember that these decisions are based not solely on the vaccine coverage or the vaccine efficacy,’ he said.
‘There’s a lot of other factors there from a societal point of view and a financial point of view and expectations of the population; for example, a bit of COVID fatigue.
‘But personally, I think, a slightly higher vaccine coverage rate plus some basic mitigation strategies in parallel, in my view, would be a better solution, if possible.’
Experts have in fact warned that dropping public health measures too soon, despite high vaccine coverage rates, could lead to further mutations of the virus.
While Associate Professor Griffin says that’s certain, he believes there is now greater knowledge, understanding and tools to be able to manage the pandemic better.
‘There are obviously vastly different approaches in a number of different countries, but hopefully we’ll learn from each other’s experiences and come up with a comprehensive solution that is feasible and relatively effective,’ he said.
‘Good control should certainly be what we aim for, not eradication or zero COVID and the constraints that go along with that.
‘We should really be able to control this so that the impact is obviously not zero, but certainly minimised.’
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