New research suggests that the covid-19 vaccine developed by AstraZeneca and Oxford University will not only offer protection against the symptoms of viral disease, but will also reduce the risk of one person transmitting the virus to others. Although scientists have been optimistic that this and other covid-19 vaccines would reduce the risk of transmission, the new data is some of the first direct evidence to support this assumption.
Researchers at Oxford University in the United Kingdom released this week’s data in a preprinted paper for the Lancet. Preprints are preliminary research papers that have not yet gone through the formal peer review process, so any conclusions should be viewed with some additional caution. Despite this, the results of the study – an analysis of long-term data from clinical trials of the vaccine in the UK and Brazil – appear to be encouraging.
On the one hand, the results suggest that even a single dose of the Oxford / AstraZeneca vaccine can be 76% effective in preventing coronavirus disease 21 days after receiving it (it is believed that it takes 21 days for the immune system to build an effective response against the virus). It is important to note that the effectiveness did not appear to decrease until three months later. The effectiveness of a two-dose regimen after three months was slightly higher, at around 82%. It is possible, the researchers theorize, that doses with an interval of three months may be the ideal regimen, since the effectiveness was lower in those who received doses with an interval of only six weeks. As other research showed, there were no coronavirus-related hospitalizations found in vaccinees after 21 days, and the vaccine was well tolerated.
The longevity of protection offered by a single dose is especially reassuring, because the UK has allowed doctors to delay administering a second dose to people for up to 12 weeks, or about three months, in order to stretch the limited supply of vaccine. Some scientists feared that a delayed-dose strategy would lead to weakened or short-term protection for some, and countries like the United States have so far not chosen to follow the UK’s example for their authorized vaccines, citing a lack of evidence for their safety. Although other data should be collected to confirm this trend, including from other vaccines with a two-dose schedule, it 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 vaccine tests have so far shown only clearly that they are effective in preventing diseases caused by the virus, not in preventing transmission from a vaccinated person to an unvaccinated one. 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 has been some initial evidence whereas other vaccines, such as the Pfizer / BioNTech injection, actually reduce transmission rates, Oxford / AstraZeneca vaccine tests have explicitly tested this possibility from the start.
Volunteers in the UK study were scrubbed for the virus regularly through PCR testing. In comparison with volunteers who received a placebo injection, who were later infected and identified by testing, the vaccinees were, on average, 67% less likely to have noticeable levels of the virus on your system, mcleaning infection. A lower risk of infection in vaccinated people should also means that they are less likely to transmit the virus. Again, this is something that more data from other studies and vaccines will have to confirm. But if it is true, it would obviously be great news to end the pandemic as soon as possible.
There are still doubts about how the spread of new variants of the virus will affect the effectiveness of these vaccines (so far, it is believed that any variants are unlikely to completely escape the immunity provided by the vaccine). In addition to science itself, the supply and distribution of these vaccines remains below ideal, especially for low-income countries. But there are also signs of improvement.
Last week, the EU authorized the emergency use of the Oxford / AstraZeneca vaccine, after authorization from the United Kingdom last December. The US Food and Drug Administration must also decide whether to authorize the Johnson & Johnson single-dose vaccine in the coming weeks (a decision on the Oxford / AstraZeneca vaccine is likely to occur after the test ends in the US in the spring). And just today, COVAX, an organization supported by several intentional public health groups and the United Nations, announced distribution forecast for the AstraZeneca / Oxford vaccine.
In the first and second half of 2021, it plans to distribute more than 330 million doses to 145 countries, along with 1.2 million doses of the Pfizer / BioNTech vaccine. These remittances are expected to cover only about 3% of people in these countries, but are expected to be enough to cover some of the most vulnerable groups, such as health professionals.