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The Delta Variant and COVID-19 Vaccines

Updated: Dec 13, 2021

The coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), has so far (through Aug 11, 2021) led to over 4 million confirmed deaths and 205 million confirmed cases of infection, worldwide. The US alone has had more than 36 million cases of SARS-CoV-2 infection and over 616,000 deaths. Notwithstanding the mind-numbing statistics of the pandemic, it should be noted that in less than 4 months after the pandemic started in Dec 2019, the first experimental doses of COVID-19 vaccine were administered to humans in clinical trials starting March 2020. While vaccines developed previously for other infectious diseases took much longer (many years to a decade), the COVID-19 vaccines were developed all over the world in less than a year and represent the fastest vaccine development programs for any disease ever.

COVID-19 due to SARS-CoV-2 Variants

Vaccine efficacy data from phase III trials have been reported and published from many companies globally. These companies include Pfizer–BioNTech, Moderna, AstraZeneca–University of Oxford, Johnson & Johnson, Gamaleya, Sinovac Biotech, Sinopharm, Novavax, and Bharat Biotech. Some of these vaccines were reviewed in detail in previous blogs and published White Papers. Furthermore, there are additional vaccines in phase III testing that have yet to report data and include vaccines which are in phase III clinical trials but not yet released data: Inovio, AnGes, ReiThera, the Chinese Academy of Medical Sciences, the Research Institute for Biological Safety Problems, Kazakhstan; Shifa, the Center for Genetic Engineering and Biotechnology, Cuba; Clover, COVAXX, the Finlay Institute, Cuba; Sanofi–GlaxoSmithKline, VECTOR, and Medicago. While improving understanding of the disease pathophysiology has led to better clinical management, the increasing percentage of the population getting vaccinated mitigated the number of COVID-19 cases initially. Subsequently, in spite of increasing vaccinations, there were some “breakthrough infections” caused by different variants of SARS-CoV-2. The B.1.1.7 (alpha) variant, the B.1.351 (beta) variant, and the P.1 (gamma) variant all caused minor surges in different regions of the world. However, one particular variant, the B.1.617.2 (delta) variant of the virus has been responsible for a disturbing surge in cases across the globe. It is important to determine whether the current vaccines are effective against this variant. To this end, a recent study published in the New England Journal of Medicine, evaluated the effectiveness of two COVID-19 vaccines, the Pfizer–BioNTech vaccine (BNT162b2) and the AstraZeneca–University of Oxford vaccine (ChAdOx1 nCoV-19), against symptomatic disease caused by the delta variant.

Are Current Vaccines any Good?

Using a sophisticated study design, scientists from the National Institute of Health Research (NIHR) in the United Kingdom looked at effectiveness of single and two doses of both the Pfizer-BioNTech and the AstraZeneca vaccines against symptomatic infection by the Delta variant. While the Pfizer-BioNTech vaccine after two doses was 88% effective against the Delta variant, the AstraZeneca vaccine (2 doses given <6 weeks apart) was 67% effective. On the other hand, when the AstraZeneca vaccine was administered >12 weeks apart, the effectiveness increased to 81%. In two recent studies (from the Mayo Clinic, and a nursing home in Ontario) that reported their findings on medRxiv, the Moderna vaccine was found to be more effective against the Delta variant than the Pfizer-BioNTech vaccine. There are similar reports across the globe about the effectiveness of most vaccines against the Delta variant, such as a recent study from India about the effectiveness of Covaxin (Bharat Biotech) against Delta SARS-CoV-2. Interestingly, while the effectiveness of the existing vaccines against the Delta variant is not 100%, recent studies suggest that a large percentage of those vaccinated do not have as severe a reaction to the virus compared with unvaccinated people.

The Path Forward

In the US and other countries where this data was recorded, it was observed that there was a reduction of reverse transcription–PCR-positive new cases in vaccinated versus unvaccinated individuals. An astounding 2.8 billion vaccine doses have been administered thus far. While vaccines so far have been effective against infections caused by the Delta and other variants, it is important to remember that there still remains a major percentage of the world population that have not been vaccinated, including the pediatric population. Moreover, preliminary studies indicate a waning effectiveness of vaccines as time after the second dose increases. All of these challenges need to be addressed by a multipronged approach, including a potential booster vaccine dose, encouraging vaccinations, and continuing practices such as frequent handwashing, use of masks and social distancing for people who cannot be vaccinated or have a weak immune system or both. People will need to adapt to a world where the COVID-19 virus, its variants and potential new variants will likely represent new challenges in the future, hence, it is incumbent upon the population and the healthcare researchers to be vigilant going forward.


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