Source: South China Morning PostPfizer and BioNTech said on Thursday they are testing a third dose of their Covid-19 vaccine to better understand the immune response against new variants of the virus.They are also in talks with regulatory authorities about testing a vaccine modified to protect specifically against the highly transmissible new variant found in South Africa and elsewhere, known as B. 1.351, as a second arm of the same study.The companies believe their current two-dose vaccine will work against the South African…Read More