- Jul 5, 2009
Additional studies will be done to test antibody effectiveness in those with weak immune systems:
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More than 32,000 volunteers took part, mostly in America, but also in Chile and Peru.
The vaccine was 79% effective against stopping symptomatic Covid disease and 100% effective at preventing people from falling seriously ill.
And there were no safety issues regarding blood clots.
That should further reassure some EU countries that recently paused rollout of the vaccine amid concerns about a possible link.
This new trial data may also prove useful in reassuring people about how well the vaccine works to protect the elderly against Covid-19 illness.
Several countries initially would not authorise the use of the vaccine in adults over 65, citing lack of evidence.
Around a fifth of the volunteers in this trial were over 65 and the vaccine - given as two doses, four weeks apart - provided as much protection to them as to younger age groups.
Hundreds of thousands of people in the UK are already receiving the AstraZeneca vaccine every day, so these numbers are tiny by comparison.
But the results are vital for the US and should clear the way for the vaccine to be approved by regulators there within the next month or two.
Lead investigator of the Oxford University trial of the vaccine, Prof Andrew Pollard said: "'These results are great news as they show the remarkable efficacy of the vaccine in a new population and are consistent with the results from Oxford-led trials.
Health workers with previous Covid-19 infections had six times the immune response to one dose of the Pfizer jab than those who hadn't had the virus.
The researchers said this emphasised the importance of people having their second dose to provide the same "booster" effect.
Those who have had Covid should still have a second jab, though, to ensure "longer-lasting" protection.
Giving the previously-infected one dose would not be efficient, experts say.
Having two jabs gives the best chance of activating all parts of the immune system and potentially protecting against new variants.
The study, funded by the Department of Health and Social Care, was an extension of Public Health England's Siren study of healthcare workers.
While a second dose was "vital" for long-term cover, the Department of Health and Social Care said the findings showed even a single dose gave strong protection in 99% of the 237 health workers studied.
Prof Eleanor Riley, at the University of Edinburgh, said this provided "considerable reassurance that the Joint Committee on Vaccination and Immunisation's somewhat controversial decision to recommend a 12-week interval between Covid-19 vaccine doses is a safe, effective and pragmatic approach to maximising public health given current constraints".
Most studies just look at people's antibody response, but this research also measured participants' T-cells.
This harder-to-measure part of our immune system tends to respond to lots of different parts of the virus's "spike", making it important for protecting against mutations.
The vaccine is designed to help your body recognise the virus if it encounters it in the wild, but as the virus mutates it begins to look subtly different, making it harder for the body to recognise.
For people who have not had Covid, the first dose of the vaccine provided protection equivalent to having had the virus.
But for people who had had Covid in the past, the first dose gave them six times the T-cell response and almost seven times the antibody response, compared with so-called Covid "naive" people who had never been infected.
And their antibodies were better at neutralising the virus completely, making it much less likely these individuals would be able to pass the virus on to others.
India has got permission to produce Astrazenecca vaccine to increase supply in the market so that poor African countries can affordIndia is ramping up its own vaccination program, so SII exports of the AZ vaccine are being restricted:
Pfizer and fellow US firm Moderna profit from their vaccines, while AstraZeneca and US giant Johnson & Johnson are supplying theirs at cost price while the pandemic continues.
It also means that the vaccine can be used in the global Covax programme, which aims to provide about two billion vaccines to developing countries.
The decision to list the Chinese vaccine for emergency use would give a substantial boost to Covax, which is currently crippled by supply shortages, mostly caused by India halting the export of vaccines.
The vaccine made by Sinovac, called CoronaVac, has only been fully authorised for use by China, but the government has already shipped millions of doses to a number of countries, which have permitted its emergency usage.
In Asia, the biggest recipients of the vaccine are Indonesia, Malaysia, the Philippines, Thailand and Pakistan, while in the Americas, Brazil, Mexico, Chile, Colombia and Ecuador have ordered millions of the jabs.
In Europe, Turkey and Ukraine have signed large contracts for Sinovac.
The vaccine is also thought to be particularly important for African countries, where so far Zimbabwe, Somalia, Djibouti, Benin and Tunisia have received vaccines from China.