Effectiveness of every vaccine against Delta variant, according to best studies

The highly infectious Delta variant is causing a resurgence of COVID-19 cases worldwide, from India all the way to the United States. Studies have found that this particular mutation allows the virus to evade the immune responses that are produced by the vaccines.

And the question on everyone’s mind right now is: how effective are the current vaccines against this variant?Business Insider has compiled all the data from the best and latest studies and here is the run down.

British study

In May, a study conducted by health officials in England revealed that two doses of AstraZeneca or Pfizer vaccines were highly effective against the Delta variant, starting two weeks after the second dose. Public Health England released the results showing that Pfizer had 33% efficacy after one dose, and 88% after the second. While AstraZeneca had 33% efficacy with the first, and 60% after the second.

Canadian study

According to a Canadian study published on 3 July, two doses of the vaccine were as efficacious against the Delta strain as with the Alpha variant—which is another variant of concern. The study has yet to be peer reviewed, but the findings showed that Pfizer was 87% effective against the variants after two doses. As for AstraZeneca and Moderna, they only had enough data to assess the rate after the first dose and they found that the AZ vaccine was 67% effective 14 days after the first dose and Modern was at 72%.

Israeli study

More recently, an Israeli study found that the Pfizer vaccine was slightly less effective against the Delta variant that previous research suggested. The Israeli Ministry of Health announced on 6 July that the BioNTech vaccine is only 64% effective after two doses.

Scottish study

Finally a Scottish study has found more promising results which revealed that Pfizer was 79% effective against the variant of concern after two doses. AstraZeneca on the other hand didn’t perform as well, with just 60% efficacy rate after two weeks of getting the second jab.

Why do the numbers differ?

Vaccine efficacy depends on the proportion of people who are fully protected after getting jabbed. If a vaccine has an 80% efficacy rate, it means that 80% of people are fully protected while the remaining 20% are not. Measuring vaccine effectiveness in the real world is challenging because no one can control who gets vaccinated. There are also many other factors that come into play but Stephan Evans, a professor of medical statistics at the London School of Hygiene & Tropical Medicine told Insider that in general, the vaccines seem to be more effective if the symptoms caused by the variant are more serious. However, he also added that there is no concrete evidence of the vaccine’s effectiveness yet.