Vaccines ‘highly effective’ among majority of at-risk groups: UK study

Jolyon Attwooll

12/07/2021 4:29:08 PM

The research relied on results from more than 700 general practices and addresses a previously unresolved information gap.

Vaccine vials.
Both the Pfizer and AstraZeneca vaccinations showed high levels of vaccine efficacy for most clinical risk groups.

The wide-scale, ‘real world’ study suggests that, in most cases, people with underlying health conditions that make them more susceptible to severe COVID-19 disease benefit from COVID-19 vaccination.
The research was funded by Public Health England and its authors have stated that it addresses a gap in evidence about administering the vaccine to those with underlying health conditions.
‘A range of clinical comorbidities have been associated with more severe COVID-19 disease and poor outcomes,’ the study says.
‘Diabetes, severe asthma, chronic heart disease, chronic kidney disease, chronic liver disease, neurological disease, and disease or therapy associated with immunosuppression have all been linked to an increased risk of hospitalisation or death with COVID-19.
‘COVID-19 vaccines have been found to be highly effective in general population cohorts; however, data on effectiveness among individuals with clinical conditions that place them at increased risk of severe disease is limited.’
The authors concluded vaccination is ‘highly effective’ in the majority of cases – particularly after two doses. 
However, there have been queries expressed about the study since it was published late last week, with the head of a blood cancer charity saying its findings are too sweeping.
The analysis was carried out from December last year until last month, allowing for the vaccines’ efficacy in those clinical risk groups to be assessed against a number of different strains, although the Delta variant only became dominant in the UK towards the end of the study.

Nevertheless, the authors concluded that for most clinical risk groups, the immune response to vaccination was maintained and both the Pfizer and AstraZeneca vaccinations showed ‘high levels of vaccine efficacy’.
‘Reduced antibody response and vaccine effectiveness were seen after one dose of vaccine among the immunosuppressed group; however, after a second dose there is only a small and non-significant reduction in vaccine effectiveness [compared to the general population],’ the authors wrote.
Researchers used electronic health record data, with the cohort representing around 10% of the country’s population – including anonymised data from more than 700 general practices across England.
The final numbers comprised a total of 5,642,687 people, including 1,276,517 over the age of 65 years and 1,054,510 within an identified risk group.
The authors suggest protection against hospitalisation and death in at-risk groups is likely to be greater than the shielding against symptomatic disease – as has been found in the population as a whole – but also acknowledge that more data is required to form stronger conclusions.
In at-risk groups aged over 65, vaccine effectiveness against infection with Pfizer is estimated at 89%, while AstraZeneca provided 80% protection against infection after two vaccine doses.
Vaccine effectiveness is cited as 81% after two doses of AstraZeneca among clinically at-risk groups aged between 16–64, with no data available in this group for the Pfizer vaccine.
For those who are immunosuppressed, vaccine effectiveness after a second dose is stated at 74% and described as offering ‘similar protection to those who are not in a risk group’. The level of protection is cited as only 4% after a first dose.
However, the study was most circumspect about this category.
‘When stratifying into groups of specific conditions the only group where [vaccine effectiveness] was notably diminished was the immunocompromised group,’ its authors noted.
In an update to the study, authors recommend people in this category seek advice from their specialists.
This followed sharp criticism from the CEO of Blood Cancer UK, Gemma Peters, who said the report presented too simplistic a headline and that its ‘confident assertions’ about protections for blood cancer patients were not yet supported by the ‘wider body of evidence’.
Also noted in the press release about the study is the UK’s detailed consideration of a potential booster vaccination program for later this year. This would look at offering a third dose for at-risk adults aged 16 years and older, with a second phase possibly including boosters for their household contacts.
While the preprint study largely relates to a time before the Delta variant became the dominant strain in the UK, another study published last month suggests the vaccines remain highly effective in preventing hospitalisation and serious illness caused by the B.1.617.2 strain.
Its analysis suggests the Pfizer vaccine is 96% effective at preventing hospitalisation after two doses compared to 92% for the AstraZeneca vaccine.
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