One dose of the Pfizer-BioNTech vaccine, which began to be used on 8 December 2020, was shown to be 71.4 per cent effective (95 per cent confidence interval [CI] 46.5-90.6) from 14 days after one dose at preventing symptomatic illness severe enough to result in hospitalisation. The patients studied had a median age of 87 years.
One dose of the Oxford-AstraZeneca vaccine, which began to be used on 4 January 2021, was shown to be 80.4 per cent effective (95 per cent CI 36.4-94.5) from 14 days after one dose at preventing symptomatic illness severe enough to result in hospitalisation. The patients studied had a median age of 88 years.
When observations were reconciled to cover the same time period in early 2021, the observed effectiveness of one dose of the two vaccines were almost identical (Pfizer-BioNTech 79.3 per cent and Oxford-AstraZeneca 80.4 per cent).
These are similar to findings from other studies from Scotland and England made public in recent days. However, the approach taken was different. Instead of linking large databases of test results, immunisation records and diagnostic codes for entire populations, this study involved comprehensive and detailed examination of all medical admissions in two admitting hospitals in a single city. This means that the dates of onset of symptoms could be accurately recorded and included in the analysis and compensation made for possible biases due to rapid changes in the vaccine rollout and the transmission of SARS- CoV-2 that occurred during the last three months.
The study also provides very detailed information on the patients who were hospitalised and in whom the vaccines are taking effect. This was a group of very elderly, frail people with many other illnesses and vulnerabilities and it is particularly remarkable that vaccination was able to protect such high-risk people so effectively.
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