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Comparing vaccines is tricky, especially at warp speed

Looking at all cases, efficacy among about 2600 early AstraZeneca recruits who received a lower first dose was 90 per cent, compared with 62 per cent among the 8800 who received two standard doses. However, these results carry greater uncertainty than those from the Pfizer trial, due to smaller numbers. Importantly, some of those in the AstraZeneca trial were tested weekly for COVID-19, with or without symptoms; efficacy against asymptomatic infection in the group who received a low first dose was 59 per cent, compared to 4 per cent in the standard dose group.

Was it the lower first dose or the time between doses that mattered in the AstraZeneca trial? According to data given to the UK regulator, the Medicines and Healthcare products Regulatory Agency, levels of the neutralising antibody in the blood (what is used to see if the vaccine kills the virus in the test tube) were about three times higher if the second dose was given 12 weeks after the first, rather than six weeks, regardless of whether one dose was low or both were standard. This suggests that a later second dose is better, which makes sense because it is what we see with other vaccines. It also puts debate about the evils of delaying the second dose into context, but is a preliminary result needing confirmation with bigger numbers.

Looking at all the detailed results from vaccine trials, not just the headline numbers, is the hard work that expert advisory committees like the Australian Technical Advisory Group on Immunisation do before any vaccine is rolled out across the population. Putting more timely, detailed information about this group’s work in the public domain would reassure people, especially at this time of understandable public anxiety.


Elimination? Globally, I suspect what is achievable is strong protection against severe disease by vaccination, with reduced, but continuing, virus circulation. The protection seen in reported trials of COVID-19 vaccines, especially for the elderly, is far superior to current influenza vaccines, even in a good year. The silver lining is that global efforts on COVID vaccines have resulted in a quantum leap forward for vaccine development generally, which is likely to translate into improvements in protection against other respiratory pathogens, even if boosters are required.

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