Elderly receive good protection with these two Covid-19 vaccines

An 86-year-old British woman gets a dose of the AstraZeneca/Oxford Covid-19 vaccine, which provides about 86% antibody protection five to six weeks after the first dose, as her 90-year-old husband looks on. — AFP

People aged over 80 receiving a single dose of either the Pfizer/BioNTech or AstraZeneca/Oxford Covid-19 vaccines show equivalent antibody responses five weeks post-vaccination.

However, stronger cellular (T cell) responses were seen in those who had received the AstraZeneca/Oxford vaccine.

Antibodies detect and kill invading microorganisms outside the body’s cells, while T cells detect and kill those invaders hiding inside the cells.

The study, led by University of Birmingham researchers in the United Kingdom and supported by the UK Coronavirus Immunology Consortium, is available via Preprints with The Lancet.

This means that it has not yet been peer-reviewed.

The study is the first to directly compare antibody and cellular immune responses between different Covid-19 vaccines in any age group.

The UK and some other countries have adopted a programme in which the interval between the first and second doses of a Covid-19 vaccine is extended to increase population coverage for the first dose.

Both the Pfizer/BioNTech and AstraZeneca/Oxford vaccines show good clinical effectiveness after a single dose, but it is important to understand the differential immune responses generated by different vaccination platforms.

This is particularly true for older people as their immune systems function less effectively than younger people, and they are the highest risk group for Covid-19.

Researchers collected blood samples from 165 people who were 80-99 years of age and living independently.

Seventy-six people had received one dose of the Pfizer/BioNTech vaccine and 89 had received one dose of the AstraZeneca/Oxford vaccine.

Samples were collected five to six weeks after the first vaccine dose.

A range of assays were used to compare the immune response generated by the vaccines, including SARS-CoV-2 protein spike-specific antibody and T cell responses.

The protein spike-specific antibodies were present in the majority of people in both groups: 93% after the Pfizer/BioNTech vaccine and 87% after the AstraZeneca/Oxford vaccine.

Similar levels of antibody response were found after both vaccines.

T cell responses were observed in fewer people from both groups.

It was detectable in only 12% of the Pfizer/BioNTech vaccine group, but three times higher at 31% in the AstraZeneca/Oxford vaccine group.

Eight participants showed evidence of previous natural SARS-CoV-2 infection.

When compared against donors without prior infection, their antibody and T cell responses after the vaccine were significantly higher (691-fold increase and four-fold increase respectively).

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/BioNTech or AstraZeneca/Oxford Covid-19 vaccines.

This reassuring level of antibody immunity from a single dose of either vaccine is likely to underpin the encouraging clinical protection seen with them.

The relatively lower rates of T cell response observed may reflect the reduced immune function that is generally observed in older people.

It remains to be seen if the different levels of T cell response recorded after each vaccine will have any impact on clinical effectiveness.

Study first author and Birmingham’s National Institute for Health Research academic clinical lecturer Dr Helen Parry said: “We know that both the Pfizer/BioNTech and AstraZeneca/Oxford Covid-19 vaccines show good real-world effectiveness, but we also need to understand the underlying immune responses that they generate.

“This is particularly so in relation to the extended dose schedu-ling of up to 12 weeks between vaccinations and its impact in older people.

“In our study, we were able to detect antibody responses in most people aged 80 or above, five weeks after a single dose of either the Pfizer/BioNTech or AstraZeneca/Oxford Covid-19 vaccines.

“These antibody responses are very encouraging as they back up the strong real-world data we are seeing in the UK.

“We also found a greater proportion of those vaccinated with the AstraZeneca/Oxford vaccine had a detectable cellular immune response, compared with those who received the Pfizer/BioNTech vaccine.

“We now need to carry out further research to understand what this difference in T cell responses means and how we might work to optimise future vaccination strategies.”