Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study | The BMJ


Participants aged 80 years and older vaccinated with BNT162b2 before 4
January 2021 had a higher odds of testing positive for covid-19 in the
first nine days after vaccination (odds ratio up to 1.48, 95% confidence
interval 1.23 to 1.77), indicating that those initially targeted had a
higher underlying risk of infection. Vaccine effectiveness was therefore
compared with the baseline post-vaccination period. Vaccine effects
were noted 10 to 13 days after vaccination, reaching a vaccine
effectiveness of 70% (95% confidence interval 59% to 78%), then
plateauing. From 14 days after the second dose a vaccination
effectiveness of 89% (85% to 93%) was found compared with the increased
baseline risk. Participants aged 70 years and older vaccinated from 4
January (when ChAdOx1-S delivery commenced) had a similar underlying
risk of covid-19 to unvaccinated individuals. With BNT162b2, vaccine
effectiveness reached 61% (51% to 69%) from 28 to 34 days after
vaccination, then plateaued. With ChAdOx1-S, effects were seen from 14
to 20 days after vaccination, reaching an effectiveness of 60% (41% to
73%) from 28 to 34 days, increasing to 73% (27% to 90%) from day 35
onwards. On top of the protection against symptomatic disease, a further
43% (33% to 52%) reduced risk of emergency hospital admission and 51%
(37% to 62%) reduced risk of death was observed in those who had
received one dose of BNT162b2. Participants who had received one dose of
ChAdOx1-S had a further 37% (3% to 59%) reduced risk of emergency
hospital admission. Follow-up was insufficient to assess the effect of
ChAdOx1-S on mortality. Combined with the effect against symptomatic
disease, a single dose of either vaccine was about 80% effective at
preventing admission to hospital with covid-19 and a single dose of
BNT162b2 was 85% effective at preventing death with covid-19.

Vaccination with either one dose of BNT162b2 or ChAdOx1-S was
associated with a significant reduction in symptomatic covid-19 in older
adults, and with further protection against severe disease. Both
vaccines showed similar effects. Protection was maintained for the
duration of follow-up (>6 weeks). A second dose of BNT162b2 was
associated with further protection against symptomatic disease. A clear
effect of the vaccines against the B.1.1.7 variant was found.


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