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COVID-19: Immunology, vaccines and epidemiology
COVID-19: Immunology, vaccines and epidemiology

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2.2 Comparison of vaccines

As noted previously, it is difficult to directly compare vaccines which have undergone phase-3 trials in different countries or at different times. However it is possible to make some comparisons between vaccines in defined studies. Figure 5 shows antibody production produced by the Oxford/AstraZeneca (AZ) and Pfizer/Biontech vaccines in different age groups and in people with previous SARS-CoV2 infection. Antibodies were measured by an assay that is similar to the ELISA you have used (called RocheS) and the results on the y-axis are expressed as titres. The results are shown as ‘violin plots’, where the width of the ‘violin’ at any particular titre reflects the number of individuals having that level of antibody.

Diagram displaying antibody responses after two doses of ChAdOx1 (AZ) or BNT162b2 (Pfizer) in different subject groups.
Figure _unit8.2.3 Figure 5 Antibody responses after two doses of ChAdOx1 (AZ) or BNT162b2 (Pfizer) in different subject groups. (Note that the plot of antibody titres is logarithmic.)
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Diagram displaying antibody responses after two doses of ChAdOx1 (AZ) or BNT162b2 (Pfizer) in different subject groups.

The y-axis is labelled RocheS and starts at the bottom with 1 and goes up, 10, 100, 1000 10000 finishing at 100000.

The x-axis is labelled, from left to right: AZ 45-64, AZ 65-84, AZ 85+, Pfizer 19-29, Pfizer 65-84, all with past infection: AZ, all with past infection: Pfizer, all with past infection: unvaccinated.

Figure 5 Antibody responses after two doses of ChAdOx1 (AZ) or BNT162b2 (Pfizer) in different subject groups. (Note that the plot of ...

ITQ _unit8.2.2

  • In the age 65-84 age group, which vaccine produced the stronger antibody response? What is the median titre, indicated by the white dot at the centre of the violins.

  • In this age group, the AZ vaccine has a median titre of just over 1000. The Pfizer vaccine has a median titre just below 10,000. So the Pfizer vaccine produces a stronger antibody response in this study.

ITQ _unit8.2.3

  • What effect does vaccination have on antibody titres in people who have been previously infected?

  • Both vaccines produce approximately a 100x increase in antibody titres in previously infected individuals, in comparison with previously infected, unvaccinated subjects. This result demonstrates the value of vaccination, even in individuals who have had a natural COVID-19 infection.