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Jolyon Attwooll
Jolyon Attwooll
A new study has examined the impact of COVID-19 boosters for those with more than one chronic condition.
A booster dose could reduce the mortality risk of COVID-19 for adults with comorbidities by up to 90% compared to those who only received two doses, a new study suggests.
In an article published this week in the Canadian Medical Association Journal, researchers from the University of Hong Kong compared the impact of third doses of both Pfizer and the CoronaVac vaccines.
The retrospective cohort study looked at clinical records of adults aged 18 and over from public healthcare facilities in Hong Kong from 11 November 2021 until 31 March 2022, as the Omicron variant became globally dominant. Death related to COVID-19 was the primary outcome the researchers considered.
The authors acknowledge multimorbidity as a ‘prevalent risk factor’ for COVID-19, and say their work seeks to evaluate the link between boosters and COVID-19 mortality in this group.
Data from 120,724 Pfizer recipients, 72% of whom had received a booster, and 127,318 CoronaVac recipients with 75% recorded as having a booster, was included in the research.
The study only included people who had at least two of 30 chronic conditions such as high blood pressure, diabetes and chronic kidney disease.
Both groups were followed up after a median of 34 days for the Pfizer group, and 38 days for the CoronaVac cohort.
Among Pfizer recipients, the booster group had five COVID-19-related deaths compared to 34 within the two-dose group, while there were 26 deaths among those with the CoronaVac booster and 88 among those who had one fewer dose.
‘Among people with multimorbidity, booster vaccination with [Pfizer] or CoronaVac was associated with reductions of more than 90% in COVID-19-related mortality rates compared with only two doses,’ the authors state.
‘These results highlight the crucial role of booster vaccination for protecting vulnerable populations as the COVID-19 pandemic continues to evolve.
‘They also highlight the potential benefit from booster vaccination, specifically in vulnerable populations living with multimorbidity, and support the recent focus on older people and those with chronic conditions for future booster doses of SARS-CoV-2 vaccines beyond the first booster.’
While previous studies have indicated the effectiveness of boosters against infection, severe disease and death, the authors note their findings stand out.
‘Our estimates of 95% reduced risk among those with [Pfizer] booster vaccination are possibly the highest risk reductions reported to date, plausibly because of the selection of a high-risk population with multimorbidity, although the adopted age was as low as 18 years,’ the study reads.
Authors also raise the waning of protection offered by the first and second doses as another possible explanation for the difference, with the number of days registered since the second dose averaging more than 180 days among the study cohort.
The latest COVID-19 vaccination rollout statistics in Australia show that more than one in every four people aged 16 and over are yet to have a booster dose. In the over-65s, the most at-risk age group, 92.4% of have received a third dose – more than seven percentage points fewer than those who have taken the initial vaccination course.
A previously redacted passage from the Halton Report, which was commissioned by the Federal Government to consider Australia’s COVID-19 vaccine and treatment procurements, pointed towards a lack of awareness regarding the boosters’ importance, as well as ‘inconsistent messaging from health authorities’ and hesitancy as factors behind a slower booster uptake rate.
‘While Australia has had early success with managing the pandemic, further emergence of new variants and management of the vaccination rollout has seen waning performance in comparison to other countries,’ the report noted.
The most recent mortality statistics published by the Australian Bureau of Statistics (ABS) indicate the pandemic’s ongoing impact, with 14,407 deaths recorded in 2022 where people died with or of COVID-19, while further registrations are still expected.
The most deaths occurred in the 80–89 age group, with provisional figures reporting 2497 males and 2027 females as having died from the data that is currently available.
The latest ABS report indicates 16% more deaths compared to expectations in 2022 until the end of October, while the Actuaries Institute COVID-19 Mortality Working Group calculates 13% more than predicted for the year until the end of August.
In the Hong Kong study, researchers calculate the incidence of death related to COVID-19 for the Pfizer booster group as 1.3 per million person-days compared to 23.4 for the two-dose group. For the CoronaVac group the same calculation stood at 5.3 and 53.1 respectively.
The authors also outline some limitations to their work, including that people with multimorbidity ‘may be better educated, more health aware and more proactive in health-seeking behaviours’ and that they may be better at self-care to minimise the risk of COVID-19.
‘Thus, the analysis may overestimate the effectiveness of the booster dose,’ they wrote.
‘Nevertheless, people in the comparison cohort had already received two doses, and such an overestimation, if any, should be minimal and may not affect the results substantially.’
The authors also note the outcome was set as ‘death with COVID-19’ rather than ‘death from COVID-19’, the latter of which they say was not feasible to establish due to the limited information in the electronic health records.
They also highlight that the 30 chronic conditions included for the study group is ‘far from exhaustive’.
However, the authors state that, as the vaccination records were provided by the lone operator of the vaccine rollout in Hong Kong along with a unified recording system and linked clinical records from territory-wide public healthcare, the ‘data should be highly reliable and representative’.
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