Are vaccines keeping up with Delta?

Jolyon Attwooll

13/07/2021 3:36:34 PM

The efficacy of vaccines against the latest variant of concern is under intense scrutiny. Here’s what the latest studies have found.

Coronavirus microscope image
The World Health Organization predicts the Delta strain will be responsible for 90% of new infections by the end of August.

There has been no shortage of reminders about the potentially devastating impact of the B.1.617.2 ‘Delta’ SARS-CoV-2 variant recently, as cases and hospitalisations continue to rise in New South Wales and infections slowly spread to other parts of the country.
The NSW Chief Health Officer Kerry Chant said on Friday there were 43 COVID-19 patients in hospital, including 14 aged under 55 and seven under the age of 35. Since then, the number of hospitalised patients in the state has risen to 63, including 18 in ICU, while at the time of publication another 63 are being treated in hospitals from Brisbane to Perth. 
Meanwhile, the US Centers for Disease Control and Prevention believes the Delta variant has become the dominant strain circulating in that country, following a similar trend seen in many other parts of the world.
In response, the international medical and scientific community has published a number of studies that consider the efficacy of vaccines against this highly infectious variant of concern.
newsGP sums up the latest findings.
WHO report
The World Health Organization (WHO) focused on variants in its latest weekly epidemiological update, predicting Delta’s impact will continue to expand while confirming it is now present in 104 countries.
‘An estimated 90% of new SARS-CoV-2 infections are expected to be due to Delta by the end of August,’ the update states.
The WHO update also highlights data from Scotland which suggests people with Delta infections are more at risk of being hospitalised than those with previously dominant strains, a trend that seems to be reflected in Sydney’s current outbreak.
The update also stresses, however, that reductions in efficacy should be not be correlated as diminishing the protection against chronic illness. It also concludes that vaccines protect against severe disease in Delta, with a ‘possible’ reduction in protection against symptomatic disease and infection.
Read the full report.
Nature manuscript
Named Delta by the WHO on 31 May, the B.1.617.2 variant was the focus of a study published in Nature on 8 July.
Its findings seem to underline the much greater efficacy that two doses of the Pfizer and the AstraZeneca vaccines have in neutralising the virus, compared to just one dose.
Using an infectious Delta strain isolated from a returned traveller, researchers examined its sensitivity to antibodies present in people convalescing from COVID-19, as well as vaccine recipients, and compared it to other viral strains.
‘Sera from convalescent patients collected up to 12 months post symptoms were 4-fold less potent against variant Delta, relative to variant Alpha [B.1.1.7]. Sera from individuals having received one dose of Pfizer or AstraZeneca vaccines barely inhibited variant Delta,’ they wrote.
‘Administration of two doses generated a neutralising response in 95% of individuals, with titres 3-to-5-fold lower against Delta than Alpha.’
The article, written by Department of Virology researchers at the Institut Pasteur in Paris, comes with a disclaimer that it is an unedited manuscript, provided early as a service to the authors and readers. A further review is planned before it appears in its final form.
Read the full report.
Israeli Department of Health
Findings made public last week suggest the efficacy of the COMIRNATY vaccine has seen a ‘marked decline’ in Israel over the past month, although Pfizer has said it is too early to draw conclusions.
‘From the epidemiological analysis by public health services in the Ministry of Health, it is evident that since June 6th there was marked decline in the effectiveness of the vaccine in preventing infection [64%] and symptomatic illness [64%],’ the Israeli Department of Health said in a statement.
‘This decline has been observed simultaneously with the spread of the Delta variant in Israel.’
Less widely publicised, however, was the Ministry’s conclusion surrounding the vaccine’s impact on preventing serious disease.
‘Nevertheless, the effectiveness of the vaccine in preventing serious illness and hospitalisation cases is estimated at 93%,’ the release stated.
The Ministry of Health also explained how it defined the vaccine’s efficacy, as contrasted to its success in preventing serious disease.
‘When the vaccine has 100% effectiveness, there will not be a single case among all vaccinated individuals,’ a follow-up statement read.
There were no details included in the Israeli announcements about the relative impact of one dose or two doses of the vaccine in neutralising the Delta variant.
Over the weekend, Reuters reported Israel will offer the Pfizer vaccine as a booster to people with weak immune systems, who according to new research may receive less protection from even two doses of vaccine compared to the general population.
New England Journal of Medicine
A special report was published last week in the New England Journal of Medicine on SARS-CoV-2 variants and vaccines.
It stressed that if variants increase in transmissibility or virulence, ‘the importance of efficient public health measures and vaccination programs will increase’.
Its authors suggest if vaccination is targeted in certain areas or demographic groups with a high incidence of infection, rather than just focusing on those at high risk of serious disease, it ‘could slow transmission and reduce the risk of development of additional variants of concern’.
They warn, however, that ‘no strategy can work if adequate vaccine supplies are unavailable’.
The report also highlights the key aim of preventing acute sickness, and has a reassuring conclusion on the vaccines’ impact for now. 
‘Additional variants that are responsible for many deaths, such as B.1.617.2, continue to emerge,’ the authors write. ‘So far, there is no good evidence that currently identified variants of concern evade the most important vaccine effect – that of prevention of severe disease.’
Read the full report.
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