Despite its higher transmissibility, research continues to show that the authorized COVID-19 vaccines protect against the Delta variant. The latest evidence comes to us from the UK.
With US public health officials recommending COVID-19 booster shots for all Americans this fall, the internet is awash in claims that the original vaccines proved to be ineffective against the circulating SARS-COV-2 variants. “The entirety of the Western world’s public health bureaucracies have not spoken a single word of truth,” economist Paul Craig Roberts wrote recently. “The vaccine does not protect you. To the contrary, it makes you ill.”
Quite a few studies say otherwise, and now we can add another to the list. A research team led by Oxford University evaluated the efficacy of the Pfizer-BioNTech, AstraZeneca and Moderna shots in more than 740,000 vaccinated individuals in the UK. They looked at the periods December 1, 2020, to May 16, 2021, when Alpha was the primary variant of concern; and May 17, 2021, to August 1, 2021, when Delta took its place. The study “investigated variation in vaccine effectiveness by long-term health conditions, age (18-34 versus 35-65 years), interval between first and second vaccination (<9 weeks versus ≥9 weeks), and prior infection.”
While the Pfizer-BioNTech and AstraZeneca shots were less effective against the Delta variant than the Alpha variant, both vaccines provided similar levels of protection against infection by the study's end. They weren't able to reach a definitive conclusion for the Moderna shot because they only evaluated its efficacy after a single dose. However, it's likely just as effective as the other two.
“The results from this large community surveillance study show that vaccination with two doses of BNT162b2 or ChAdOx1 still significantly reduces the risk of new PCR-positive SARS-CoV-2 infections,” the researchers wrote.
The study confirmed that vaccinated individuals can transmit the virus under certain circumstances, though this possibility needs to be considered in its proper context, because
a greater percentage of virus may be non-viable in those vaccinated, and/or their viral loads may also decline faster as suggested by a recent study of patients hospitalized with Delta, leading to shorter periods 'at risk' for onwards transmission.
The authors warned that we shouldn't assume vaccination inevitably results in “a low risk of onward transmission.” Still, the study provides more evidence that the shots prevent infection and, by extension, reduce transmission. University of Oxford researcher Sarah Walker summed it up in a sentence: "Both of these vaccines are still doing very well against Delta."
But Israel!
The skeptics will inevitably point to the recent research out of Israel indicating that 60 percent of hospitalized COVID-19 patients were fully vaccinated. If this seems like a slam dunk to you, you're not looking at the data closely enough. Jeffrey S. Morris, Director of Biostatistics at the Perelman School of Medicine at the University of Pennsylvania, helpfully did the math, so we didn't have to.
First of all, Morris explained, almost 80 percent of Israel's population is vaccinated. When you compare that vaccinated group to the unvaccinated, you see a dramatically lower rate of severe disease in the former—5.3 vs. 16.4 cases per 100,000 people. But there's more. When you stratify by age, as Morris did, you get an even clearer picture:
Vaccine efficacy vs. severe disease for younger (<50yr) = 1 - 0.3/3.9 = 91.8% Vaccine efficacy vs. severe disease for older (>50yr) = 1- 13.6/90.9 = 85.2% These efficacies are quite high and suggests the vaccines are doing a very good job of preventing severe disease in both older and young cohorts. These levels of efficacy are much higher than the 67.5% efficacy estimate we get if the analysis is not stratified by age.
Another caveat
As more people get infected and develop immunity, it's easy to minimize the efficacy of vaccines. "This will cause an apparent drop in [vaccine effectiveness] VE over time, even if the vaccine keeps working as well as ever," biologist Carl Bergstrom wrote on Twitter. "Imagine a vaccine that has 90% VE when no one in the population has natural immunity. If half the unvaccinated population acquires (perfect) natural immunity, VE drops to 80%."
With all that said, this new UK study confirms the results we've seen in previous research. The vaccines show some reduced efficacy against Delta relative to other variants, though immunization still protects you from infection and severe disease.
