New research suggests that the covid-19 vaccine developed by AstraZeneca and the University of Oxford not only provides protection against the symptoms of viral diseases, but also reduces the risk of someone transmitting the virus to others. Although scientists were optimistic that these and other vaccines against covid-19 would reduce the risk of transmission, the new data is one of the first direct pieces of evidence to support the assumption.
Researchers at Oxford University in the UK released the data this week in a preprint paper for the Lancet. Pre-prints are preliminary research articles that have not yet gone through the formal peer review process. Therefore, any conclusions should be considered with extra caution. Regardless, the findings from their study – a long-term analysis of data from clinical trials of the vaccine in the UK and Brazil – appear to be encouraging.
The results suggest that even a single dose of Oxford / AstraZeneca vaccine can be 76% effective in preventing coronavirus disease 21 days after it is received (it is thought to take 21 days for the immune system to build up an effective response against the virus). It is important that the effectiveness does not decrease until three months later. The effectiveness of a two-month two-dose regimen was approximately 82%. It is possible, according to the researchers, that doses of three months apart may be the best schedule, as the effectiveness was lower in those who received the doses only six weeks apart. As other research has shown, no coronavirus-related hospitalizations were found in those vaccinated after 21 days, and the vaccine was well tolerated.
The longevity of the protection offered by a single dose is particularly reassuring, as the UK has allowed doctors to give the second dose to people for up to twelve weeks or about three months to expand the limited vaccine supply. Some scientists were concerned that a delayed-dose strategy would lead to weakened or short-term protection for some, and countries, including the US, have so far not chosen to follow the lead of the United Kingdom for their authorized vaccines. . . Although other data need to be collected to confirm this trend, also of other vaccines with a two-dose course, this is a sign that a delayed dose may not be too risky, at least for the Oxford / AstraZeneca vaccine. .
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Many scientists have been careful to note that these vaccination trials have so far only clearly shown that they are effective in preventing diseases of the virus, and not in preventing transmission from a vaccinated person to a vaccinated person. Still other experts have argued that it would be very unlikely that a vaccine would reduce the risk of the former, but not the latter. Although there were some early testimony that other vaccines, such as the Pfizer / BioNTech shot, are indeed lowering transmission speeds, the Oxford / AstraZeneca vaccine trials have explicitly tested for that possibility since the beginning.
Volunteers in the British trial were regularly administered by means of PCR tests for the virus. Compared to the volunteers who received a placebo survey, who later became infected and identified through testing, those who were vaccinatedon average 67% less noticeable levels of the virus in their system, minfection. A lower risk of infection in vaccines should also means they are less likely to transmit the virus. Again, this is something that needs to confirm more data from other trials and vaccines. But if this is true, then of course it would be good news to end the pandemic as soon as possible.
There are still questions about how the spread of new virus variants will affect the efficacy of these vaccines (so far it is unlikely that any variants will completely escape the immunity provided by the vaccine). In addition to science itself, the supply and distribution of these vaccines are still sub-optimal, especially in low-income countries. But there are also signs of improvement.
Last week, the EU authorized the emergency use of the Oxford / AstraZeneca vaccine, following the British authorization last December. The US Food and Drug Administration is also expected to decide to approve the vaccine for Johnson & Johnson in the coming weeks (a decision on the Oxford / AstraZeneca vaccine is likely to follow after the end of the US trial in the spring). And just today, COVAX, an organization supported by several intentional public health groups and the United Nations, announced its distribution forecast for the AstraZeneca / Oxford vaccine.
In the first and second half of 2021, it is planned to distribute more than 330 million doses to 145 countries, together with 1.2 million doses of Pfizer / BioNTech vaccine. These shipments are expected to cover about 3% of the people in these countries, but it is hoped that this will be enough to cover some of the most vulnerable groups, such as health workers.