Is Delta more deadly to the unvaccinated?

The hand-wringers and head-shakers were out in force for the grave news. Headlines tolled like church bells for the impending doom: Delta is more deadly than the national plan assumes, Delta variant more deadly than first thought

Chip Le Grand of the Sydney Morning Herald declared that the ‘debate appears at an end, with both the Doherty and the Burnet institutes adopting the findings of a Canadian study showing unvaccinated people infected with Delta are nearly twice as likely to end up in intensive care and one-and-a-half times more likely to die as people who caught the Alpha variant.’

Sounds ominous…or does it?

What’s important to understand up front is that the original Pfizer trials were not actually designed to study severe disease’. According to Peter Doshi of the British Medical Journal: ‘In the data that supported Pfizer’s EUA, the company itself characterized the “severe covid-19” endpoint results as “preliminary evidence.” Hospital admission numbers were not reported, and zero covid-19 deaths occurred.’

In light of that, let’s take a look at this preprint Canadian study. While it’s true that it does use the word ‘deadly’, it is worth digging a little deeper to find exactly how the authors came to this conclusion.

Interestingly, it appears that more than a little speculation was involved: ‘As hospitalization, ICU admission and death were fortunately relative [sic] rare among cases, we considered odds ratios to approximate relative risks under the “rare disease assumption” and constructed “mixed effects logistic regression models”.’ 

So…they kinda just guessed? 

As to the data regarding who was considered to be vaccinated, it turns out that this was a little murky: ‘Individuals were categorized as fully vaccinated if the case episode date occurred 7 or more days after receipt of the second dose; partially vaccinated if the case episode date occurred 14 days or more after receipt of the first dose but less than 7 days after receipt of the second dose; and unvaccinated otherwise.’ 

Huh? So if you had your first shot on a Monday and then contracted COVID-19 on the Saturday, you’d be officially classified as ‘unvaxxed’? Granted, this isn’t exactly a new tactic – in fact, the CDC doesn’t count you as fully vaccinated until two weeks after your second shot – but it sure has the potential to skew the data. 

Another red flag is the ‘conflict of interest’ section. Dr David N. Fisman (one of the two authors of the study) just happens to be on several vaccine advisory boards (for Pfizer and Astrazeneca). Let’s hazard a guess that he isn’t advising AGAINST administering the shots. 

So how does the Canadian study compare to other emerging data about the Delta variant? Let’s take a look.

  • ‘The Delta variant is highly contagious and breakthrough infection to fully vaccinated individuals is often observed, suggesting that neutralizing antibodies in fully vaccinated individuals are not sufficient to protect against infection by the Delta variant.’ 
  • ‘In our more recent data (since mid-April 2021), infections and hospitalisations began to re-converge, potentially reflecting the increased prevalence and severity of Delta compared with Alpha, a changing age mix of severe cases, and possible waning of protection…. without additional interventions, increased mixing during the autumn in the presence of Delta variant may lead to renewed growth, even at high levels of vaccination.’
  • ‘During June–July 2021, when B.1.617.2 (Delta) variant circulation predominated, effectiveness declined significantly to 53.1%.’
  • ‘This study demonstrated that natural immunity confers longer lasting and stronger protection against infection, symptomatic disease and hospitalization caused by the Delta variant of SARS-CoV-2, compared to the BNT162b2 two-dose vaccine-induced immunity.’ 
  • ‘…[O]ur data suggest that vaccine effectiveness against any symptomatic disease is considerably lower against the delta variant and may wane over time since vaccination.’ 
  • ‘The attack rate among exposed individuals reached 23.3% in patients and 10.3% in staff, with 96.2% vaccination rate among exposed individuals. Moreover, several transmissions probably occurred between two individuals both wearing surgical masks, and in one instance using full PPE, including N-95 mask, face shield, gown and gloves.’ 
  • Risk of COVID-19 hospital admission was approximately doubled in those with the Delta VOC when compared to the Alpha VOC, with risk of admission particularly increased in those with five or more relevant comorbidities… [T]here was no evidence of a differential vaccine effect on hospital admissions among those first testing positive.

What does all this mean? In layman’s terms, there are a number of reasons to be concerned at waning vaccine efficacy, the vaccines’ growing inability to combat the Delta variant and the reality that ‘breakthrough cases’ (ie. getting COVID-19 after vaccination) are becoming all the more common. 

When we break it down, it seems that the whole picture doesn’t exactly lean towards the simplistic ‘vaccine = good/unvaccinated = bad’ dichotomy. In fact, the evidence is increasingly tilting the other way. Particularly with Nature’s recent findings that even ‘mild infection with SARS-CoV-2 induces robust antigen-specifc, long-lived humoral immune memory in humans.’ 

Perhaps the Burnet Institute (which also happens to be behind the mask study roundly condemned as ‘crap’ last week) would be well-served looking deeper into all the evidence, not simply the studies that reinforce preconceived opinions. 

References regarding Vaccine Trials

Will covid-19 vaccines save lives? Current trials aren’t designed to tell us (Peter Doshi, BMJ)

Does the FDA think these data justify the first full approval of a covid-19 vaccine? (Peter Doshi, BMJ)

Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine (NEJM)

SARS-CoV-2 Variants of Concern in the United States—Challenges and Opportunities (JAMA)

References regarding the Delta variant

The SARS-CoV-2 Delta variant is poised to acquire complete resistance to wild-type spike vaccines (Preprint)

REACT-1 round 13 final report: exponential growth, high prevalence of SARS-CoV-2 and vaccine effectiveness associated with Delta variant in England during May to July 2021 (Spiral, ICL, May to July 2021)

Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August 1, 2021 (CDC Study)

Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections (Preprint with The Lancet)

Resurgence of SARS-CoV-2 Infection in a Highly Vaccinated Health System Workforce (New England Journal of Medicine)

Nosocomial outbreak caused by the SARS-CoV-2 Delta variant in a highly vaccinated population, Israel, July 2021 (Eurosurveillance)

SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness (The Lancet, April-June 2021)

SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans (Nature)

Other references

Progressive Increase in Virulence of Novel SARS-CoV-2 Variants in Ontario, Canada (Preprint)

When You’ve Been Fully Vaccinated (CDC)

‘It’s crap’: Victorian study claiming mandatory masks stopped second wave shredded by experts (News.com.au)


1 The SARS-CoV-2 Delta variant is poised to acquire complete resistance to wild-type spike vaccines (Preprint)

2 REACT-1 round 13 final report: exponential growth, high prevalence of SARS-CoV-2 and vaccine effectiveness associated with Delta variant in England during May to July 2021 (Spiral, ICL, May to July 2021)

3 Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August 1, 2021 (CDC Study)

4 Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections (Preprint with The Lancet)

5 Resurgence of SARS-CoV-2 Infection in a Highly Vaccinated Health System Workforce (New England Journal of Medicine)

6 Nosocomial outbreak caused by the SARS-CoV-2 Delta variant in a highly vaccinated population, Israel, July 2021 (Eurosurveillance)

7 SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness (The Lancet, April-June 2021)

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