LONDON: An eight-week gap between the first and second doses of the Pfizer/BioNTech Covid-19 vaccine is a “sweet spot” when it comes to generating strong immune response while protecting the UK population against the Delta variant of coronavirus, scientists have said.
In a new study, funded by the Department of Health and Social Care (DHSC), researchers have found that when compared to a four-week gap, a 10-week interval between the doses produces higher antibody levels, as well as a higher proportion of a group of infection-fighting cells in the body known as “helper” T cells.
At the start of the second wave of the Covid-19 epidemic, the Joint Committee on Vaccination and Immunisation (JCVI) made a decision to recommend a 12-week gap between two doses for the two vaccines that were available at the time: Pfizer and Oxford/AstraZeneca.
Professor Susanna Dunachie, of the University of Oxford, who is the joint chief investigator in the Pitch study, said: “The original recommendation from JCVI was 12 weeks and this was based on a lot of knowledge from other vaccines that often having a longer interval (between doses) gives your immune system a chance to make the highest response.
“The decision to put it to eight weeks is really balancing all the wider issues, the pros and cons – two doses is better than one overall. Also, other factors need to be balanced, (such as) vaccine supply, the desire to open up, and so on.”
She added: “I think that eight weeks is about the sweet spot for me, because people do want to get the two vaccine (doses) and there is a lot of Delta out there right now. Unfortunately, I can’t see this virus disappearing so you want to balance that against getting the best protection that you can.”
For the Pitch study, the researchers recruited 503 healthcare workers, 44 per cent (223) of whom previously had Covid-19, and studied the immune responses generated by the Pfizer jab. They found that both short (three to four-week) and long (10-week) dosing intervals of the Pfizer vaccine generated strong antibody and T cell immune responses. But the longer schedule led to higher antibody levels and a higher proportion of helper T cells, which according to the researchers, supports immune memory.
The scientists found that after the second dose, a wider gap also resulted in higher neutralising antibody levels against the Delta variant and all other variants of concern.
But in this instance, antibody levels dropped off between first and second dose – leaving the recipients vulnerable against the Delta variant after one jab.
The researchers said there may be exceptions where the dosing schedule may need to be shortened from eight weeks to four, such as for those who are about to have treatments that may affect the immune system, such as cancer or organ transplant.