Vaccine Efficacy Comparisons Between Alpha and Delta Variants

Very helpful article summarizing the data in Financial Times today.

On preventing symptomatic infection, early data from real-world studies in the UK in May found two doses of Pfizer were 88% effective against Delta. Similar analyses in Scotland showed 79% effectiveness.

In Canada, preliminary analyses estimated that Pfizer was 87% effective at preventing infection with the Delta variant. I will post more info on the Canadian study as a stand-alone.

In Israel, the health ministry suggested Pfizer was much less effective against symptomatic infection with Delta, providing only 64% protection (see previous post on this). Effectiveness against severe illness and hospitalization was still over 90%. However, there were many methodological flaws with this including a highly localized data set, so the findings should be considered preliminary and not ready for extrapolation.

Real-world analysis of 14,000+ cases of the Delta variant in the UK by Public Health England found that two doses of Pfizer and AstraZeneca were 96% and 92% effective against hospitalization.

So as I had mentioned earlier, while we do need to monitor the data closely for Delta variant, effectiveness of the vaccines still seems fairly high against Delta. But because no vaccines offer 100% protection, breakthrough infections are possible and it becomes even more important to protect those who are immunocompromised or those unable/ineligible to get vaccinated in our communities.