Over the coming weeks and months, we can expect a large number of preprints and papers reporting ‘breakthrough infections’, i.e. infections in vaccinated individuals.

Prof Francois Balloux

Most studies on ‘breakthrough infections’ will likely be statistically underpowered. Yet the ones with the most lurid and alarmist message will probably get most media coverage and attention.
In anticipation, I’d like to make a few points already.

A proportion of breakthrough infections are expected. Otherwise, vaccine trials would all have reported 100% efficacy.

Breakthrough infections are a trivial concern as long as they don’t lead to serious disease in the infected, and onward transmission of the virus remains limited.

The frequency of breakthrough infection is expected to be highest soon after after the first jab and go down over time. For vaccines with two doses, it is questionable whether infections prior to the booster should even be referred to as ‘breakthrough infections’.

Breakthrough infection frequency is expected to vary for different #SARSCoV2 ‘variants’. Though at this stage, there is no ‘vaccine escape’ viral lineage in circulation, despite claims to the contrary.

Breakthrough infection frequency is expected to vary between demographies, i.e. highest in those least able to mount a robust immune response.

Evidence for increased breakthrough rates of SARS-CoV-2 variants of concern in BNT162b2 mRNA vaccinated individuals


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