New research suggests that the covid-19 vaccine developed by AstraZeneca and Oxford University will not only provide protection against the symptoms of the viral disease, but will also reduce a person’s risk of transmitting the virus to others. Although scientists have been optimistic that this vaccine and other covid-19 vaccines would reduce the risk of transmission, the new data are some of the first direct evidence to support this assumption.
Researchers at Oxford University in the UK released data this week 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 greater caution. Regardless, the results of their study – an analysis of longer-term data from vaccine clinical trials in the UK and Brazil – appear to be encouraging.
First, the results suggest that even a single dose of Oxford / AstraZeneca vaccine may be 76% effective in preventing coronavirus disease 21 days after receiving it (it is thought to take 21 days until the immune system creates an effective response against the virus). Importantly, efficacy does not appear to decrease until three months later. The effectiveness of a two-dose, three-month regimen was slightly higher at about 82%. The researchers say that doses three months apart may be the optimal schedule, as efficacy was lower in those who received doses just six weeks apart. As other research has shown, no coronavirus hospitalizations were found in those vaccinated after 21 days, and the vaccine was well tolerated.
The longevity of single-dose protection is particularly reassuring, as the UK has allowed doctors to delay giving people a second dose for up to 12 weeks, or about three months, to extend the limited supply of the vaccine. Some scientists have worried that a delayed-dose strategy would lead to weak or short-term protection for some, and countries, including the US, have so far chosen not to follow the UK’s example of licensed vaccines. evidence for its safety. . Although other data should be collected to confirm this trend, including from other two-dose vaccines, it is a sign that a delayed dose may not be too risky in the end, at least for the Oxford / AstraZeneca vaccine.
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Many scientists have carefully observed that these studies on vaccines have so far only shown that they are effective in preventing diseases caused by the virus, not in preventing transmission from a vaccinated person to an unvaccinated person. However, other experts have done so supported that a vaccine would be very unlikely to reduce the risk of the former, but not the latter. Although there were some early evidence that other vaccines, such as the Pfizer / BioNTech shot, do have lower transmission rates, studies on Oxford / AstraZeneca vaccines have explicitly tested this possibility from the outset.
Study volunteers in the UK were regularly swabbed with the virus by PCR tests. Compared to volunteers who received a placebo shot who subsequently became infected and were identified by tests, those who were vaccinated were, on average, 67% less likely to have visible levels of the virus in their system, meaning infection. A lower risk of infection in vaccinated people should also means that it is less likely to transmit the virus. Again, this is something that will need to be confirmed by more data from other studies and vaccines. But if it’s true, it would obviously be great news to end the pandemic as soon as possible.
There are still questions about how the spread of new virus variants will affect the effectiveness of these vaccines (so far, it is believed that any variant is unlikely to completely get rid of the immunity offered by the vaccine). Beyond science itself, the supply and distribution of these vaccines continues to be sub-optimal, especially in lower-income countries. But there are signs of improvement there as well.
Last week, the EU authorised emergency use of the Oxford / AstraZeneca vaccine, after UK clearance in December last year. The US Food and Drug Administration is also expected to decide whether to authorize the Johnson & Johnson single-dose vaccine in the coming weeks (a decision on the Oxford / AstraZeneca vaccine is likely to follow after the US study is completed in the spring). And today, COVAX, an organization supported by several public health groups and the United Nations, has announced its distribution forecasts 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 Pfizer / BioNTech vaccine. These shipments 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 workers.