The United Kingdom's controversial decision to delay the second dose of the AstraZeneca (NASDAQ AZN)-Oxford University coronavirus vaccine may have inadvertently been an effective strategy for combating the nation's outbreak.
According to a new study conducted by Oxford researchers, the vaccine was 76% effective at preventing symptomatic infection for three months after one dose, with the efficacy rate actually increasing the longer length of time between the first and second doses.
The efficacy rate increased to 82.4% with at least 12 weeks between doses, and when the second dose was given in less than 6 weeks the rate dropped to 54.9%. Currently, the vaccine's recommended dosing regime is about 4 weeks between doses, with the vaccine being about 70% effective at preventing severe COVID infection.
The study, which is under review to be published by The Lancet, also found there to be a 67% reduction in viral transmission rates after the first dose of the vaccine, based on nasal swabs taken from volunteers.
"The exploratory analyses presented in this preprint suggest that it is the dosing interval and not the dosing level which has a great impact on the efficacy of the vaccine," said Professor Andrew Pollard, chief investigator of the Oxford Vaccine Trial and co-author, in a statement. "This is in line with previous research supporting great efficacy with longer prime-boost intervals down with other vaccines such as influenza, Ebola and malaria."
The U.K.'s current vaccination strategy, that has been approved by the nation's Joint Committee on Vaccination and Immunisation, is to inoculate as many people as possible with the first dose of a coronavirus vaccine, and then to delay the second dose for up to three months. This strategy is to make sure more people have at least partial protection against the virus.
In another controversial strategy, the U.K. initiated a clinical trial on Thursday the will study the immune responses in participants that receive one dose of the AstraZeneca vaccine and another of the vaccine developed by Pfizer
The trial will first administer one dose of the Pfizer-BioNTech shot to healthy volunteers. That shot will then be followed by a booster of AstraZeneca's vaccine with intervals of 4 and 12 weeks between. The trial will also study immune responses in participants first given the AstraZeneca shot then the Pfizer shot with each of the two interval gaps.
The researchers behind the study expect to present some early results by June.
The vaccines developed by AstraZeneca-Oxford and Pfizer-BioNTech are the only approved for emergency use in the U.K. AstraZeneca's vaccine is also approved for emergency use by the European Union.
