Full vaccination with AstraZeneca offers 92% protection against hospitalisation with delta variant

With the delta variant, both AstraZeneca and Pfizer vaccines offer high protection against hospitalisation. One dose of AstraZeneca vaccine offered 71% protection against hospitalisation, while two doses offered 92% protection. In the case of Pfizer vaccine, the protection against hospitalisation was 94% after one dose and 96% after two doses.

A real-world study undertaken by Public Health England in 14,019 people infected with the delta variant (B.1.617.2) in England found that vaccination with two doses of AstraZeneca and Pfizer offered high protection against hospitalisation. Of the 14,019 people infected with the delta variant, only 166 required hospitalisation. The study was undertaken between April 12 and June 4.

In the case of AstraZeneca, effectiveness against hospitalisation after full vaccination was 92%, while it was 96% in the case of Pfizer.

The results have been posted as a preprint. Preprints are yet to be peer-reviewed.

Public Health England had earlier found that despite modest reductions, vaccines remain effective against the delta variant. It found that in the case of the delta variant, full vaccination offered good protection against symptomatic disease. Vaccine effectiveness against symptomatic disease after two doses was 67% in the case of AstraZeneca and 88% with Pfizer.  

Effectiveness against hospitalisation was high even with one dose of AstraZeneca and Pfizer vaccine. In the case of the delta variant, one dose of AstraZeneca vaccine offered 71% protection against hospitalisation, while two doses offered 92% protection. In the case of Pfizer vaccine, the protection against hospitalisation was 94% after one dose and 96% after two doses.  

“These are comparable with vaccine effectiveness against hospitalisation from the Alpha variant ” says a PHE release.

“These findings indicate very high levels of protection against hospitalisation with the delta variant with one or two doses of either vaccine,” the authors write. “Understanding the effectiveness against more severe end points such as hospital admissions is crucial in evaluating the risk delta variant poses on the population.”

“It is absolutely vital to get both doses as soon as they are offered to you, to gain maximum protection against all existing and emerging variants,” Dr Mary Ramsay, Head of Immunisation at PHE, said in the release.

“One dose effectiveness against hospitalisation [with the delta variant] of the AstraZeneca vaccine was 71% and two doses were 92%. This is reassuring data for India. In order to choose our way forward, I think we should use modelling approaches that lay out different implementation strategies and compare their impact at different stages of the pandemic,” says Dr. Gagandeep Kang, Professor of Microbiology at CMC Vellore.

Another study posted as a preprint on May 24 found that protection against all symptomatic infections after a single dose of AstraZeneca was only 33.5% against the delta variant and 51.1% against the beta (B.1.1.7) variant. After the second dose, the protection against all symptomatic infections increased to 59.8% in the case of the delta variant and 87.9% against the beta variant. 

These studies indicate that even if vaccines offer relatively less protection against symptomatic infection, the effectiveness against severe disease that require hospitalisation is far higher.

Published in The Hindu on June 15, 2021