USA: Vaccine breakthough cases in Washington State by coronavirus variant to 30th June 2021

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Washington State has recently published an update on the number of vaccine breakthrough cases.

Importantly, the update shows which Sars-CoV-2 variant is responsible for 661 of those cases through genome sequencing.

This hugely important information is not available for most states in the USA, so the fact that Washington State continues to publish this information for the Covid variants currently circulating in that state makes it all the more valuable.  Spoiler alert: Delta B.1.617.2 is NOT YET the most common variant for vaccine breakthrough cases in Washington State! That situation will almost certainly change over the next few weeks as Delta becomes more dominant across the U.S.

The most common variant currently causing vaccine breakthroughs in Washington State up to 30th June 2021 is Alpha, (B.1.1.7),  at 37%, followed by Gamma (P.1) at 17%. The Delta variant (B.1.617.2) currently only accounts for about 5% of vaccine breakthrough infections.

The Epsilon variant (B.1.429) is showing as being responsible for 15% of all breakthrough cases, yet represents just 3% of the total genome sequences for May to June, and never rose above 10% of genome samples from April 2021.

Washington State data on all breakthrough cases:

Source: Washington State Vaccine Breakthrough Report


Sars-CoV-2 variants circulating in Washington State April – June 2021:


Source: Washington Covid-19 Dashboard

As you can see, Washington State has recorded 2,228 vaccine breakthrough cases in total which represents a tiny fraction of the 6 million people now vaccinated in that state.

Our thanks to The Washington State Department of Health for providing this vital information.


USA: Washington State Vaccine Breakthroughs by Variant up to 14th July 2021


USA: Washington State Vaccine Breakthroughs by Variant up to 7th July 2021


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** This post was originally published on July 4, 2021 **