27 June 2022
Vaccines saved millions, but could have saved more
And fourth doses are a lifesaver in aged care facilities.
Your weekly pandemic wrap from Australia and around the world.
- Covid vaccines prevented an estimated 14 million deaths in first year after release.
- Fourth vaccine dose reduces risk of death in aged care residents by nearly 75%.
- Omicron reinfection can occur in under 60 days, especially in young and unvaccinated.
- Delta wave in Australia saw one in five ICU beds occupied by a covid patient.
- Global covid infections and deaths still declining, but Omicron BA.4 and BA.5 rising.
Covid vaccines are likely to have saved more than 14 million lives globally in the first year they were available, but substantially more deaths could have been averted through equitable access to vaccines.
A modelling study published in The Lancet Infectious Diseases used country-level data to compare infection and death trajectories, as well as excess deaths, before and after the introduction of covid vaccines. The modelling included data on vaccine uptake in each country, and vaccine efficacy based on the type of vaccines.
It suggested that vaccines reduced global covid deaths by 63% – i.e. 14.4 million deaths were avoided between December 2020, when the vaccines were first introduced, to December 2021.
However, in low-income countries, lower availability and uptake of vaccines mean that their benefit was far less. Had all low-income countries achieved the 40% vaccination coverage target that had been set by WHO for the end of 2021 – and 96 of them didn’t – a further 600,000 deaths could have been avoided in those countries.
Aged care residents receiving a fourth dose of covid vaccine have a 72% reduction in the risk of death and 64% reduction in the risk of hospitalisation from Omicron infection, research suggests.
A paper published in JAMA Internal Medicine reports the outcomes of a prospective cohort study involving 24,000 aged care residents who received a fourth dose of vaccine, and nearly 20,000 who had had only three doses, and who were followed for a median of 73 days after the most recent vaccine dose.
A fourth dose was also associated with a 34% lower risk of infection and a 67% lower risk of hospitalisation for severe infection compared to only three doses.
Reinfection with Omicron’s subvariants can occur within as little as three weeks of the first Omicron infection, prompting one group to suggest that the minimum retesting interval after first infection should be shortened.
Writing in Emerging Infectious Diseases, researchers report data from more than 58,000 people who tested positive for covid in early 2022, 0.01% of whom showed evidence of reinfection with BA.2 after initial infection with BA.1.
The time between first and second infection ranged from 17 days to 65 days, and early reinfections were more common in those who were unvaccinated or partly vaccinated.
“Previous retrospective cohort studies showing a prolonged maintenance of protection against reinfection should be questioned after the emergence of Omicron,” the authors wrote.
At the height of the Delta wave, nearly one in five intensive care beds in Australia was occupied by a covid patient, and the risk of dying in hospital from covid was nearly ten percentage points greater than in the first two waves.
A paper in the Medical Journal of Australia examined 2493 intensive care admissions at 59 facilities during the first, second and third waves of the covid pandemic in Australia.
Four-fifths of admissions occurred during the Delta wave, from June to November 2021, during which time just over 19% of intensive care patients had covid compared to 2.8% in the first wave and 4.6% in the second wave.
While the median lengths of hospital stay, intensive care stay or intubation were all shorter during the third wave compared to the first wave, in-hospital mortality was nearly 10 percentage points higher.
The authors suggested the greater in-hospital mortality may have been the result of the more severe and transmissible Delta variant, as well as changes to public health prevention measures and overloading of healthcare infrastructure.
Global covid infections and deaths are still declining, with the latest WHO figures showing a 4% drop in new infections and 16% drop in deaths in the past week.
The Omicron sub-variant BA.4 and BA.5 are still rising in prevalence, with mutations suggesting both have increased transmissibility compared to the original Omicron variant. However WHO says there is still no evidence of increased severity with the subvariants.