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COVID-19 vaccines highly effective in most people in clinical risk groups — Massive UK study

The Pfizer/BioNTech and AstraZeneca/Oxford COVID-19 vaccines are as effective at preventing symptomatic illness in people with underlying medical conditions as in the rest of the UK population, reports MedicalBrief. This emerged from a real-world study by Public Health England of more than one million at-risk people.

A team led by PHE researchers mined the electronic medical records of more than 700 general-practice clinics across the country, representing 10% of the population. They also conducted sentinel antibody testing from December 2020 to May 2021

Within these clinical risk groups, said PHE in a statement, there would be people with more severe forms of illness – particularly in the immunosuppressed group – who might not respond as well to the vaccines, and it was recommend they seek advice from their specialists.

The study found overall vaccine effectiveness against symptomatic disease in risk groups is approximately 60% after one dose of either AstraZeneca or Pfizer-BioNTech, with little variation by age. After two does, vaccine effectiveness is 81% with AstraZeneca in people in risk groups aged 16 to 64. No data is available for Pfizer-BioNTech. In people in risk groups aged 65 and over, vaccine effectiveness with Pfizer-BioNTech is 89% and 80% with AstraZeneca. The authors said for those who are immunosuppressed, vaccine effectiveness after a second dose is 74%, with similar protection to those who are not in a risk group. This rises from 4% after a first dose.

Although age is the greatest risk factor for adverse outcomes after coronavirus infection, certain health conditions also increase the risk of severe disease. Diabetes, severe asthma, chronic heart disease, chronic kidney disease, chronic liver disease, neurological disease, and diseases or therapies that weaken the immune system – such as blood cancer, HIV or chemotherapy – have all been linked to an increased risk of hospitalisation or death with COVID-19.

People with these conditions who are at highest risk were initially advised to shield during the peak of the pandemic and all risk groups were then prioritised for vaccination

The government announced the dose interval would be brought forward from 12 to 8 weeks for the clinically vulnerable on 14 May, and everyone in these groups should now have been offered a second dose.

Data on vaccine effectiveness among people in clinical risk groups were previously limited. Though more data are needed, protection against hospitalisation and death in risk groups is expected to be greater than protection against symptomatic disease, as has been seen in studies of the general population.

Dr Mary Ramsay, head of immunisation at PHE, said: “These real-world data show for the first time that most people who are clinically vulnerable to COVID-19 still receive high levels of protection after two doses of vaccine. “It is vital that anyone with an underlying condition gets both doses, especially people with weakened immune systems as they gain so much more benefit from the second dose.”

The Joint Committee on Vaccination and Immunisation (JCVI) advised that those living with immunosuppressed adults should be prioritised for vaccination to help limit the spread of the virus to people in this group. If the planned booster programme goes ahead, the JCVI has recommended that immunosuppressed adults and their household contacts should also be among the first to be offered a third dose of vaccine in September.

PHE estimates that 30,300 deaths and 8,151,000 infections have been prevented as a result of the COVID-19 vaccination programme, up to 25 June. This is based on modelling analysis from PHE and Cambridge University’s MRC Biostatistics Unit.

PHE also estimates that 46,300 hospitalisations have been prevented in people aged 65 or older in England up to 27 June (approximately 7,000 admissions in those aged 65 to 74, 18,000 in those aged 75 to 84, and 21,300 in those aged 85 and over).

Study details

Pfizer-BioNTech and Oxford AstraZeneca COVID-19 vaccine effectiveness and immune response among individuals in clinical risk groups

Heather Whitaker, Ruby SM Tsang, Rachel Byford, Nick J Andrews, Julian Sherlock, Praveen Pillai, John Williams, Elizabeth Button, Helen Campbell, Mary Sinnathamby, Georgina Pike, Sneha Anand, Ezra Linley, Jacqueline Hewson, Ashley Otter, Joanna Ellis, Richard FD Hobbs, Maria Zambon, Mary Ramsay, Kevin E Brown, Simon de Lusignan, Gayatri Amirthalingam, Jamie Lopez Bernal

Published on khbb July 2021


A range of clinical comorbidities has been associated with more severe COVID-19 disease and poor outcomes. COVID-19 vaccines have shown high levels of efficacy in older adults, healthcare workers and the general population in both clinical trials and real-world effectiveness studies in general population cohorts. However, data on effectiveness among individuals with clinical conditions that place them at increased risk of severe disease is limited.

We use GP electronic health record data, sentinel virology swabbing and sentinel antibody testing within a cohort of more than 700 general practices across England (representing 10% of the population) to estimate antibody response to vaccination and vaccine effectiveness against medically attended Covid-19 among individuals in clinical risk groups.

Adjusted prevalence ratios of S-antibody positivity and titres after vaccination were estimated by clinical risk group. Adjusted vaccine effectiveness was estimated using a cohort analysis and a nested test negative case control analysis.

There was no notable reduction in S-antibody positivity or titres in most clinical risk groups. The only clinical risk group with significantly reduced S-antibody response after one and 2 doses was the immunocompromised group who had a 68% (95%CI: 43 to 82%) reduction in the geometric mean titre after 2 doses. Reduced vaccine effectiveness against clinical disease was also noted in the immunosuppressed group after one dose, however, after a second dose of either vaccine, high levels of effectiveness were seen (Pfizer: 73.0%, 95%CI 33.9 to 89.0%; AstraZeneca 74.6%, 95%CI 18.7 to 92.1%).

In most clinical risk groups, immune response to vaccination is maintained and high levels of vaccine effectiveness are seen with both the Pfizer and AstraZeneca vaccines. 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. These findings would support maximising coverage with two doses in immunosuppressed individuals.


KHUB report: Pfizer-BioNTech and Oxford AstraZeneca COVID-19 vaccine effectiveness and immune response among individuals in clinical risk groups


See more from MedicalBrief archives:


'UK moves from pandemic to endemic situation’ — 2 Oxford studies


Updated pooled analysis of 3 Oxford/AstraZeneca vaccine trials


Benefits of mix-and-match approach to COVID-19 vaccines


Single shot of AstraZeneca or Pfizer-BioNTech vaccines reduce hospital treatment for elderly


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