A health worker shows a vial of the Covid-19 coronavirus vaccine from AstraZeneca-Oxford at Patan Hospital near Kathmandu on January 27, 2021.
PRAKASH MATHEMA | AFP | Getty Images
The UK's decision to postpone AstraZeneca University Oxford's second shot of coronavirus vaccine has proven to be an effective strategy, according to the results of a new study.
Oxford University researchers found that the Covid-19 vaccine was 76% effective at preventing symptomatic infection for three months after a single dose, and that the rate of effectiveness increased with a longer interval before the first and second dose.
"The effectiveness of the vaccine after a single standard dose of the vaccine from the 22nd to the 90th day post-vaccination was 76% … and the modeled analysis showed that protection did not diminish during this initial 3-month period," said the Study that was reviewed by The Lancet Medical Journal and published as preprint on Tuesday found.
The effectiveness rate increased to 82.4% when at least 12 weeks were before the second dose. When the second dose was given less than six weeks after the first, the rate of effectiveness was 54.9%.
"These analyzes show that greater vaccine effectiveness is achieved with a longer interval between the first and second dose and that a single dose of vaccine is highly effective in the first 90 days, which further supports current policy," the report said .
The UK's current strategy is to vaccinate as many people as possible with a single dose first and delay the second dose for up to 12 weeks. The idea is that a first dose will provide at least some of the protection and allow more people to have access to the vaccines while their availability is limited.
The decision to delay the administration of a second booster dose has sparked controversy, with some questioning whether it might reduce the effectiveness of the vaccine in preventing severe Covid-19 infection.
However, the UK Joint Committee on Vaccination and Immunization supported the approach. The UK is also delaying the second dose of Pfizer BioNTech vaccine, a move vaccine makers have warned about, arguing that there is no data to support a delay.
The study also provided important data on whether the vaccine reduced transmission of the virus, a previously unknown and crucial question for policy makers looking to lift measures to lock down the economy.
Based on weekly swabs from volunteers in the UK study, a 67% reduction in transmission was found after the first dose of the vaccine.
This latest study supports the UK Government's decision and concludes that vaccination programs "aiming to vaccinate a large proportion of the population with a single dose, with a second dose given after a period of three months, are an effective strategy to reduce disease and may be the optimum for pandemic vaccine introduction when supply is limited in the short term. "
The study used additional data from ongoing clinical trials of the vaccine. A separate announcement from AstraZeneca on Wednesday showed that the vaccine also prevented serious illness from Covid-19, with no serious cases and no hospital stays more than 22 days after the first dose.
The vaccine was approved by the UK Medicines Agency on December 30th and, as a UK-made shot, makes up most of the country's vaccination program that has so far been hailed as a success.
The UK is well on its way to vaccinating its four top priority groups (over 70s, residents and workers in nursing homes, frontline health and social workers and the most clinically vulnerable), which number around 15 million people by mid-February to have.
By February 1, over 9.6 million people had received a first dose of the vaccine, and just under 500,000 had received two doses, according to government figures.
Professor Andrew Pollard, chief investigator of the vaccine study at Oxford and co-author of the study, said, "These new data provide an important review of the intermediate data used by more than 25 regulatory agencies, including MHRA and EMA, to grant vaccine emergency approval."
"It also supports the policy recommendation of the Joint Vaccination and Immunization Committee for a 12-week prime-boost interval as it seeks the optimal approach to initiation and assures us that people will be protected before 22 days after a single are dose of the vaccine. "
The researchers also hope to release data on the new coronavirus variants in the coming days and expect the results to be broadly similar to those already reported by other vaccine developers: that the current vaccines are effective against mutations in the virus.
Germany, France and Sweden currently do not recommend the AstraZeneca vaccine for people over 65 because of insufficient study data for this age group. However, the vaccine maker and the UK government have defended the sting, saying the data available shows it is safe and effective. Further analysis will be available shortly.