Tulane Home Tulane Shield logo linking to site home page

COVID-19 Digest focuses on delta variant

August 09, 2021 12:45 PM
Claiborne Christian cchrist6@tulane.edu

This is a special issue of the Tulane COVID-19 Digest. As the delta variant fuels a fourth surge in the US among unvaccinated individuals, media reports of breakthrough infections are receiving increasing attention. While breakthroughs can happen, the overwhelming (90%+) majority of new infections, hospitalizations and deaths are among not completely vaccinated individuals. This unvaccinated population is the primary driver of the current surge. The vaccines remain highly effective at preventing infection and exceptionally effective at preventing severe disease and death.

As the COVID-19 Delta variant fuels a massive surge in cases, the Kaiser Family Foundation finds that on average over 94%+ of reported COVID cases are in unvaccinated individuals. As compiled by KKF, around half of all states are reporting data specific to vaccinated COVID-positive individuals.  As a share of reported positive cases, all states report that vaccinated individuals make up less than 6% of total reported cases, with 20 of the 24 reporting states recording rates of 2% or less. All states report that the share of hospitalized COVID-positive patients is below 5%, while it is also important to note that because of de facto testing upon hospital admission, many of those hospitalized - or that have died after having been vaccinated - were not hospitalized because of COVID or died due to COVID. For example, according to the CDC, 27% of the reported hospitalized vaccinated COVID cases were not related to COVID/symptomatic, and in the very small number (~1000) deaths in COVID-positive vaccinated individuals, 26% were not related to COVID. Overall, these data demonstrate the effectiveness of the vaccines in preventing infection, with breakthroughs being comparatively quite rare. Additionally, they highlight the extreme efficacy of these vaccines in preventing severe disease and death, well exceeding the 50% efficacy goal set by the FDA at the outset and the 70% optimistic goal voiced by experts in early 2020. These data also clearly demonstrate that it is unvaccinated Americans that are the overwhelming primary drivers of the ongoing wave of transmission in the US. 

In what can be described as a successful stress test for COVID vaccine efficacy, the CDC reports data on an outbreak in Provincetown, MA over a high-volume tourism/holiday period. Over a period of time in which an estimated 60,000 tourists traveled to the area, an initial case cluster of 469 COVID-positive individuals were identified. According to media reports, this number has now grown to some 965 cases. This population was highly vaccinated, with 69% of the state of MA reporting complete vaccination and 74% of those testing positive.  Importantly, of the original reported cluster, only 5 (4 vaccinated, 2 with underlying medical conditions) individuals were hospitalized, with no deaths reported. These data indicate that in a highly vaccinated population, risk of severe disease is minimal. Additionally, even in the context of the highly transmissible delta variant and a highly social environment, relative to the number of potentially exposed individuals, the identified cases constitute a comparatively small percentage. Indeed, as reported in media outlets, CDC analysis of this data concluded that vaccinated individuals are 8 times less likely to be infected than unvaccinated ones. As data compiled by the KFF demonstrates, vaccinated breakthrough cases, hospitalizations, and deaths are a very small part of the overall number of COVID cases in the US, with unvaccinated individuals the primary driving force behind the current surge. 

Individuals with a combination of history of COVID and vaccination appear to have exceptionally strong protective immunity. As published in Nature (and analyzed by JAMA), individuals who had been infected (even those with mild disease) and vaccinated had over 50 times more neutralizing antibody activity than those who were unvaccinated. This level of protection was more robust even than that seen in fully vaccinated individuals. Indeed, those individuals who had both a history of COVID and were vaccinated were described as “bulletproof”. By logical extension, these data also suggest that in those proportionally rare individuals who experience breakthrough infection, that could act as a booster to the vaccine, engendering even more powerful immunity against subsequent infection and illness (though this issue will need to be specifically studied in the breakthrough population). 

Even as the COVID delta variant drives the US surge among the unvaccinated, other countries as seeing their delta peaks collapse earlier than expected. As covered in multiple media outlets, delta surges in countries like the UK and the Netherlands are collapsing faster than expected. Additionally, thanks to effective vaccine drives targeting the elderly and most at risk, mortality is over an order of magnitude less than what was seen in comparable winter waves. The reasons for the collapse are at present unclear (though Britain’s wildly successful vaccine drive likely plays a part), with experts still watching to see if the US follows a similar course (though the unique nature of vaccine uptake in the US relative to other countries makes predicting trends in spread and mortality difficult). It may be that in highly vaccinated communities the US experiences a similar sharp decline, with the fate of the highly unvaccinated pockets of the US less immediately apparent. 

STAT covers a preprint from mRNA vaccine manufactures that demonstrate that protection from COVID falls very slightly over 6 months, from 90% to 84%. This drop is most pronounced in groups known to have trouble maintaining vaccine-induced immune protection like the elderly. Based on the rate of decay, vaccines may fall below the 50% threshold in around 18 months, bolstering the companies’ argument that boosters may be necessary eventually. 

STAT reports on, how under increasing pressure from all fronts, the FDA will prioritize review of the Pfizer/BioNTech vaccine for full approval, pausing existing projects to devote full attention to this issue. Reporting and analysis from the NYT suggests that full FDA approval may be crucial in convincing some segments of the American public so far reluctant to getting vaccinated. 

STAT presents a Q&A-style analysis on the prospect of COVID-19 boosters, addressing key issues like durability of vaccine protection (more of a concern in groups like the elderly, who are known to have issues sustaining immunity from vaccines), the dialog between pharmaceutical companies and the government, and the impact of delta on vaccine boosters (data supports the idea that the vaccines as formulated are still highly protective against variants). 

Thank you for trusting us to be a source for reliable, scientific COVID-19 information. We will be back as needed to help guide our readers through this next phase of COVID-19, embodying as always Tulane’s motto of Non Sibi Sed Suis – Not for Oneself but For One’s Own.

Share The Science:  Please forward this issue and encourage others to sign up for Tulane School of Medicine’s COVID19 Daily Digest Mailing List.

Please visit the Collaborative COVID-19 Literature Review Synopses (CoCOLRS) Database for a searchable tagged index of Digest-featured and other articles. 

Curated Research and Research-Related News Summaries, Analysis, and Synthesis. Published on behalf of The Tulane University School of Medicine. Content is generated by reviewing scientific papers and preprints, reputable media articles and scientific news outlets.  We aim to communicate the most current and relevant COVID-19-related scientific, clinical and public health information to the Tulane community. In keeping with Tulane’s motto, “Not for Oneself but for One’s Own," we are making it available to anyone else who would benefit.


Claiborne M. Christian, PhD: Editor, Head Researcher, and Head Writer
Claire O'Laughlin: Copyeditor
Shannon Esher, PhD: Weekend Review Researcher
Alyssa Fears, MPH&TM: Weekend Review Researcher
Jaikin Harrell: Database Organization Manage
Amanda Harriett: Database Organization Manager
Vivian Park, MS: Weekend Review Researcher
Special thanks to James Zanewicz for ad hoc copyediting assistance.