‘Attenuated’ vaccines are more similar to the strategy pioneered by Jenner, using versions of the virus that are weakened until they lose their ability to establish disease. The chicken pox vaccine and some flu vaccines use this method. Whilst there are currently no true COVID-19 vaccines being developed in this way, in Australia and the Netherlands two Phase Three studies are looking at whether the BCG vaccine, an attenuated vaccine for tuberculosis, could provide some protection against COVID-19.