Delaying Second Pfizer COVID-19 Vaccine Dose Increases Antibody Response Threefold In Over-80s, Study Finds
Healthcare workers vaccinating at risk patients with the Pfizer-BioNTech COVID-19 vaccine in Lima, Peru.

Delaying the second dose of the Pfizer/BioNTech COVID-19 vaccine by 12 weeks could generate antibody responses in those over the age of 80 more than threefold, found a pre-print study published on Friday.

The study, conducted by the University of Birmingham and Public Health England, is the first to directly compare the immune response derived from the recommended three-week dosing interval with the extended 12-week interval.

Some 175 participants over 80 years of age were included in the study, 99 of whom received the second dose after three weeks and 73 had the second jab at 12 weeks. 

The peak antibody levels were 3.5 times higher in those who waited 12 weeks for their second shot, compared to those who waited three weeks. 

“The enhanced antibody responses seen after an extended interval may help to sustain immunity against COVID-19 over the longer term and further improve the clinical efficacy of this powerful vaccine platform,” said Paul Moss, Professor of Haematology at the University of Birmingham, in a press release. 

The peak T cell immune response, which plays a role in maintaining antibody production, was lower in those with the extended interval, but the responses were comparable between the two groups when measured at the same interval after the first dose. 

In addition, T cell levels rose two weeks following the second dose. Further research is required to understand the different T cell immune responses, said the authors. 

“This research is crucial, particularly in older people, as immune responses to vaccination deteriorate with age. Understanding how to optimise COVID-19 vaccine schedules and maximise immune responses within this age group is vitally important,” said Dr Helen Parry, lead author of the study, in a press release. 

“Individuals need to really complete their second dose when it’s offered to them because it not only provides additional protection but potentially longer lasting protection against COVID-19,” said Dr Gayatri Amirthalingam, Consultant Epidemiologist at Public Health England.

The “extension of interval of the second vaccine dose in older people may potentially reduce the need for subsequent booster vaccines,” said Moss, highlighting the use of the findings to develop global vaccination strategies.

Findings Useful in Optimizing Vaccinations, But Pfizer Vaccine not Available to Many Countries

While the findings are reassuring and could be useful in optimizing vaccination protocols and strategies, the results are specific to the Pfizer vaccine, which is largely not available to many low- and middle-income countries. In addition, in several countries where variants are spreading rapidly, the risk of infection may be higher after only one vaccine dose. 

In the United Kingdom, however, the study findings are supportive of the controversial approach taken by the government in late December to delay the second dose up to 12 weeks.The decision was made amid rising cases in an effort to expand partial immunity to more of the population. 

The study “provides further supportive evidence of the benefits of the UK approach to prioritise the first dose of vaccine,” said Dr Amirthalingam.

Experts Study Link Between COVID-19 Vaccines and Rare Blood Clots

The AstraZeneca vaccine being administered in Catalonia, Spain in mid-February.

In other vaccine news, scientists are investigating the possible connection between the AstraZeneca and Johnson & Johnson COVID-19 vaccines and rare blood clots, which have been reported across numerous countries in recent months. 

Both the AstraZeneca and Johnson & Johnson COVID-19 vaccines have been investigated by regulatory agencies for links to rare blood clots, known as cerebral venous thrombosis (CVT). Several countries, including the United States, the European Union, and South Africa, paused or limited the rollout of both vaccines due to reports of CVT.  

“Understanding the cause is of highest importance for the next-generation vaccines, because [the novel] coronavirus will stay with us and vaccination will likely become seasonal,” Eric van Gorp, Professor of Infectious Diseases at Erasmus University in the Netherlands, told the Wall Street Journal

A German research team, led by Andreas Greinacher, a transfusion medicine expert at the University of Greifswald, found that certain proteins and molecules in viral vector vaccines – which the AstraZeneca and J&J vaccines both are – could cause an autoimmune response that leads to blood clots. 

In a peer reviewed study published in the New England Journal of Medicine in April, the researchers proposed naming this type of clotting ‘vaccine-induced immune thrombotic thrombocytopenia’ (VITT).

According to Greinacher, it might be possible to reduce the risk of blood clots by removing proteins and reducing the level of the EDTA preservative in the jabs after the manufacturing process. Data would have to be collected on how this may impact the safety and efficacy of the vaccines. 

Although this is only one possible explanation for the cases of rare blood clotting and experts disagree on the exact mechanism at work, Greinacher is reportedly in communication with AstraZeneca and J&J to conduct more research on the vaccines and VITT.

“We strongly support raising awareness of the signs and symptoms of this very rare event, and we are currently exploring a potential collaboration with Dr. Greinacher,” said a J&J spokesperson. 

Image Credits: Flickr – Province of British Columbia, International Monetary Fund/Ernesto Benavides, Flickr.

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