Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant

by Marlu McLean

The recent surge in SARS-CoV2 which cause COVID-19 cases worldwide which was driven by the delta variant.  The effectiveness of the new emerging vaccines is still unknown and researchers in the United Kingdom decided to investigate the effectiveness of the vaccines (Gower et al., 2021).

Since November 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) has infected nearly 197 000 000 people and caused the death of 4 200 000 people.  This has not only burdened our healthcare systems, but economies worldwide have been shaken.  Due to the mutagenic potential of the virus, it has been able to change and adapt to overcome barriers to spreading the infection.  The delta variant was first detected in December 2020 in India, where it caused the largest wave of infections yet seen after the discovery of SARS-CoV2.  Scientists has been working on vaccines worldwide, but the efficiency of these vaccines are still uncertain and causes a lot of hesitancy among people.

A group of scientists in the United Kingdom decided to look at the effectiveness of the vaccines currently approved in the United Kingdom on the delta variant.  They looked at the effectiveness of BNT162b2 (Phizer-BioNTech) and ChAdOx1 nCoV-19(Novavax) vaccines after one and two doses. They also compared the effectiveness of the vaccine to the alpha variant.  The scientists accounted for possible confounders by looking at health seeking behaviour of the vaccinated and unvaccinated groups and looked at the effect of any vaccine compared with these two.  They used data acquired in England and used PCR tests to test for SARS-CoV2 and whole genome sequencing to determine which variant according to the spike protein, nucleocapsid and open reading frame 1ab.  The data was analysed and they also compared the results with previous studies on the alpha and delta variant which confirmed that the alpha variant control group was accurate. 

They determined that in the any vaccine group, Phizer-BioNTech and Novavax groups the effectiveness of the vaccine was more after the second dose than the first.  People who received any vaccine had an 87,5% effectiveness with the alpha and 79,6% with the delta variant.  The Phizer-BioNTech vaccine had 93,7% with the alpha and 88,0% with the delta variant.  The Novavax vaccine had an effectiveness of 74,5% effectiveness against the alpha variant and 67,0% with the delta variant.  In all three groups was there a very small difference between the alpha and delta strains. 

Ultimately was the effectiveness against the delta strain better in the group who received the two doses of the Phizer-BioNTech than the Novavax vaccine.  These results are also consistent with other studies.  This paper shows that the two vaccines studied in England had high levels of effectiveness against symptomatic disease caused by the delta variant.  The emergence of effective vaccines is a light at the end of the dark COVID-tunnel and brings hope that we would be able to win the fight against this pandemic.


Gower, C., Phil, D., Gallagher, E., Ph, D., Simmons, R., Ph, D., Thelwall, S., Ph, D., Stowe, J., Ph, D., Tessier, E., Sc, M., Groves, N., Sc, M., Dabrera, G., Myers, R., Ph, D., Campbell, C. N. J., & Amirthalingam, G. (2021). Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant. 1–10. https://doi.org/10.1056/NEJMoa2108891

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