evidence: The benefits of prime-boosting with COVID-19 vaccines were initially seen in clinical trials. Early studies of the currently approved COVID-19 vaccines compared the immune responses in people who received one or two vaccine doses. Results showed that after the second dose, people had higher amounts of antibodies to fight the virus, indicating that taking more than one dose would probably increase vaccine effectiveness. [...] The scientists investigated the antibody responses of 250 people vaccinated with the Pfizer/BioNTech vaccine against five variants of the coronavirus, including the original "wild type" that spread in early 2020 as well as the alpha and delta variants and several other forms. After the first and second dose, the researchers looked to see whether people had antibodies able to prevent infection – called neutralising antibodies – for these different forms of the virus. [...] Yet after two doses of the Pfizer/BioNTech vaccine, the paper suggests protection against symptomatic COVID-19 rises to 93% against the alpha variant and 88% for the delta variant. The Oxford/AstraZeneca vaccine also sees a lift: after a second dose it’s 66% protective against alpha and 60% effective against delta.