The first dose alone of the AstraZeneca and Pfizer vaccines triggers a strong immune response, find researchers.
The study conducted by the University of Birmingham, and the UK Coronavirus Immunology Consortium is the first of its kind to compare the performance of two vaccines.
These findings are especially reassuring at a time when the decision to delay the second dose of the AstraZeneca vaccine is creating apprehension among the recipients.
India's vaccine eligibility cap means that most of the recipients of the vaccine so far have been the elderly.
And according to the findings of the study, a longer gap between the two doses should not be a cause for concern as they start producing a strong antibody response soon after the first dose itself.
The study was conducted using the blood sample of 165 people between the ages of 80–99-years.
76 people received one dose of the Pfizer vaccine and 89 received one dose of the AstraZeneca vaccine.
5–6 weeks after the first vaccine dose, their blood samples were collected to compare their immune response.
This included Spike-specific antibody and T cell responses.
The study found that 93 percent recipients of the Pfizer vaccine and 87 percent recipients of the AstraZeneca vaccine showed the presence of spike specific antibodies.
On the other hand, when it comes to the Cellular (T cell) responses, there seemed to be a bigger gap between the two vaccines.
Only 12 percent of the Pfizer/BioNTech vaccine group showed the production of T cells against the virus, as compared to the 31 percent of the AstraZeneca group.
The strength of this cellular response was also three times higher following the AstraZeneca vaccine when compared with the Pfizer vaccine.
"These results indicate that antibody responses develop in most people over 80 years of age at five weeks after a single dose of either the Pfizer or AstraZeneca COVID vaccine," reads the study.
Eight of the participants who previously had COVID showed a far higher antibody and T cell responses after the vaccine (691-fold increase and 4-fold increase respectively).
“It is important to understand how the immune response generated by COVID-19 vaccines varies with age, the delay between doses, and the type of vaccine administered," said Paul Moss, Principal Investigator of the UK Coronavirus Immunology Consortium, and the study's corresponding author.
"The findings are reassuring because many countries, including the UK, have chosen to delay administering second doses,” he added.
The study has been published online as a reprint with the Lancet and is yet to be peer-reviewed.
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