COVID-19: 'No substantial difference' in protection offered by Pfizer and AstraZeneca vaccines, study suggests
Restrictions in the use of the Pfizer vaccine early in the rollout meant that some of the most vulnerable people were given the AstraZeneca jab instead, making it appear as if that jab was less effective.
Wednesday 20 October 2021 19:16, UK
There are "no substantial differences" in the protection offered by the UK's two main COVID-19 vaccines, a new study suggests.
Many previous studies have been done across a range of population groups showing that the AstraZeneca vaccine was less effective than the jab made by Pfizer.
However, the authors of the new study have pointed out that some of this could be due to the health of those who received the AstraZeneca vaccine.
Due to the restrictions in the transport and storage of the Pfizer vaccine - it needed to be kept at extremely cold temperatures - it was not given to many housebound people, or people in care homes.
Most of these people instead received the AstraZeneca vaccine.
Because they were already among the most vulnerable to COVID-19, they suffered from the virus in greater numbers, making the AstraZeneca jab appear less effective.
Using the OpenSAFELY database, which covers 40% of England's GP practices and is also linked to national coronavirus surveillance, hospital and death registry data, the researchers focused on healthy health workers instead.
For 20 weeks, they followed 317,341 health workers who had been vaccinated between 4 January and 28 February, finding "no substantial differences" in the incidence of infection or disease.
Just over 253,000 had been given the Pfizer vaccine and about 64,000 had received the AstraZeneca jab.
Six weeks after vaccination, there had been 19.2 infections per 1,000 people who received the Pfizer vaccine, compared to 18.9 per 1,000 who had been given the AstraZeneca vaccine, representing a difference of -0.24 per 1,000 people.
The difference in A&E attendance rates was 0.01 per 1,000 people, and for hospital admissions it was 0.03 per 1,000 people.
There were not enough examples of severe disease or death within the group to examine for the study.
The authors concluded: "In this cohort of healthcare workers where we would not anticipate vaccine type to be related to health status, we found no substantial differences in the incidence of SARS-CoV-2 infection or COVID-19 disease up to 20 weeks after vaccination.
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"Incidence dropped sharply after 3-4 weeks and there were very few COVID-19 hospital attendance and admission events after this period.
"This is in line with expected onset of vaccine-induced immunity, and suggests strong protection against COVID-19 disease for both vaccines."
The researchers did note, however, that the study was done at a time when the dominant variant was Alpha. This has since been replaced by the Delta variant, which could affect the protection offered by the vaccines.
The , done by researchers in the UK and US, has not yet been peer reviewed.