Two doses of Pfizer vaccine produce higher number of antibodies, study shows

Despite antibody positivity falling off with age, researchers find ‘very good response’ with two doses of vaccine

A new study suggests that people of all ages who received two doses of the Pfizer/BioNTech Covid-19 vaccine produce high numbers of antibodies.

However, there is insufficient data to determine how protected someone may be from coronavirus based on a positive antibody test result, and it does not mean they are immune.

The React-2 study, carried out by Imperial College London and Ipsos MORI, also gathered insight into how different groups feel about vaccines.

More than 154,000 participants used a finger prick test to test themselves at home between 26 January and 8 February, showing 13.9 per cent of the population had antibodies either from infection or vaccination.

Of those, more than 17,000 had received at least one dose of a Covid-19 vaccine.

The data indicates that 87.9 per cent of people over the age of 80 tested positive for antibodies after two doses of the Pfizer/BioNTech vaccine - rising to 95.5 per cent for those under the age of 60 and 100 per cent in those aged under 30.

The study also showed high levels of confidence in the vaccine, with more than 90 per cent of people surveyed reporting they would be willing to accept, or had already received a vaccination.

However, confidence in the vaccine carried by age, sex and also by ethnicity. 92.6 per cent of white participants showed confidence in the jab at the highest end of the scale, compared to 72.5 per cent of black participants on the lowest end.

Those showing signs of vaccine hesitancy cited three main concerns, including wanting to wait and see how the vaccine works, concern about long-term health effects and worries about side effects.

Other common concerns shown in free text comments were around current and planned pregnancy, future fertility and specific allergies or comorbidities.

Professor Paul Elliott of Imperial College London, director of the React programme, said: “Overall there’s very high effectiveness in terms of antibody positivity from two doses of the BioNTech, and also from a single dose in people who have had prior infection, that much we know.

“And also, although there is some fall off in positivity with age, at all ages we get that very good response to two doses of the vaccine.

“And in terms of the confidence in the vaccine, it’s very, very high, although there are some groups where it’s a bit low, and that includes some ethnic minority groups and some younger people,” he added.

Antibody prevalence in people who have not yet been vaccinated is highest in London (16.9 per cent), and in people of black (22.1 per cent) and Asian (20 per cent) ethnicities, and those aged 18-24 years (14.5 per cent).

The proportion  of people testing positive for antibodies when they received a single dose of the jab after 21 days was 94.7 per cent in under-30s, ranging from 73.7 per cent at 60 to 64 years to 34.7 per cent in those aged 80 and over.

A high percentage (88.8 per cent) of individuals who previously had confirmed or suspected Covid-19 tested positive for antibodies, the pre-print study found. The study has not yet been peer-reviewed.

Health secretary Matt Hancock said: “These findings shed more light on rates of antibodies across the UK and among different groups, as we continue to strengthen our understanding of Covid-19.

“It is fantastic to see over 90 per cent of people surveyed would accept or had already accepted a vaccine, as we continue to expand the rollout.

“I urge anyone who has been invited for a vaccine to book an appointment. And while we are seeing rates of the virus gradually decline it is important we all hold our resolve and follow the rules as we deliver on our cautious but irreversible approach to easing lockdown.”

The Joint Committee on Vaccination and Immunisation (JCVI) noted that in Pfizer’s clinical trial, protection against Covid-19 was very high (89 per cent) between 14 and 21 days after vaccination, despite very low levels of antibodies measured at the same time.

Researchers say this suggests that early antibody response has no correlation with clinical protection.

Professor Helen Ward, lead author for the React study of population prevalence, said: “Our findings suggest that it is very important for people to take up the second dose when it is offered.

“We know that some groups have concerns about the vaccine, including some people at increased risk from Covid-19, so it is really important that they have opportunities to discuss these and find out more.”