Covid-19: Eight-week gap between Pfizer’s first and second vaccine shot boosts immunity – UK study

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  • An eight-week gap between the first and second doses of the Pfizer vaccine results in stronger immunity against all variants of concern.
  • The results are based on antibody and T cell levels of UK healthcare workers vaccinated with the Pfizer jabs.
  • Antibody levels were not sustained for long after the first jab, highlighting the importance of being fully vaccinated.

An eight-week gap between administering the first and second doses of the Pfizer-BioNTech Covid-19 vaccine leads to the body generating a stronger immune response against Covid-19, according to the latest research from the UK. 

Although the US Centers For Disease Control and Prevention (CDC) recommend that the two-dose vaccine be given 21 days apart, emerging evidence increasingly points to longer dosing gaps providing greater benefit.

The latest study, funded by the UK Department of Health and Social Care (DHSC), analysed the immune responses of 503 NHS staff (44% of whom previously had Covid infection) who received their two shots at different intervals in late 2020 and early 2021. 

The researchers examined how antibody and T cell levels changed over time following either a "short" (3–4 weeks, average of 24 days) or "long" (6–14 weeks, average of 70 days) interval between the first and second dose of the vaccine. 

What they found

Researchers compared the difference between the short and long dosing intervals and found that both schedules generated strong immune responses overall. 

However, while the longer gap between doses led to fewer T-cells overall, it resulted in a higher proportion of a group of “helper” T-cells, which the researchers said support long-term immune memory and help generate antibodies to prevent infection. This means that the immune system would respond more rapidly and effectively to the virus if it encountered it.

As explained in this Health24 article, there are three different types of T-cells: 

  • Cytotoxic ("killer") T cells that force infected cells to self-destruct 
  • Helper T cells that coax B cells (another type of immune cell) to secrete antibodies
  • Regulatory T cells that shut off the immune response when it is no longer needed (thereby preventing excessive damage to the normal cells and body tissues) 

Importance of second dose

The research team also found that a three-week dosing interval generated fewer of the neutralising antibodies – which fight the SARS-CoV-2 virus’s ability to enter, and therefore infect, human cells – than a 10-week interval. This was tested against the Delta variant and all other variants of concern (VOC).

Antibody levels were also not sustained for long after the first dose, underscoring the importance of receiving the second dose.

The team cautioned that levels of antibodies and T cells varied significantly from person to person, which they said may depend on factors such as genetics, underlying health conditions, and past exposure to Covid-19 and other viruses.

There are also exceptions in the case of people who are immunosuppressed, such as those receiving cancer treatment, they said, and advised that they get their second doses as soon as possible.

Eight weeks the 'sweet spot'

Professor Susanna Dunachie from Oxford University, and the joint chief investigator in the Pitch (Protective Immunity from T cells to Covid-19 in Health Workers) study, said at a news briefing on Thursday 22 July that two doses provided higher protection against Covid-19 disease than one dose, but that the timing of the second dose was somewhat flexible, depending on a country’s circumstances.

Commenting about the UK’s situation, she said: "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."

Most comprehensive study to date

Dr Rebecca Payne, one of the study authors, from Newcastle University, commented that their study is one of the most comprehensive studies to look at the immune response to Covid-19 following two doses of the Pfizer vaccine.

She added: "Our study provides reassuring evidence that both dosing schedules generate robust immune responses against the virus after two doses. We now need to carry out more follow-up studies to understand the full clinical significance of our findings."

The findings were published in the pre-print server, Cell Press Sneak Peek, and have not yet been peer-reviewed.

Vaccination in SA

The UK initially extended the dosing gap to 12 weeks, but this later changed to eight weeks in the context of the highly transmissible Delta variant circulating in the country. 

The CDC also states that “up to 42 days between doses is permissible when a delay is unavoidable”.

Dr Sandile Buthelezi, Director General of South Africa’s National Department of Health recently said in a statement that, based on emerging evidence, the country’s EVDS will schedule appointments to administer the two doses of the Pfizer vaccine 42 days (six weeks) apart, Health24 reported.

“There is currently emerging evidence to support a 42-day interval between the first and second doses. The Ministerial Advisory Committee on Covid-19 Vaccines (VMAC) has reviewed the available evidence in this regard and advised that, in the event of limited vaccine supply, the dosing interval should be extended to 42 days,” she said.

People aged between 18 and 34 will be eligible to be vaccinated from September, President Cyril Ramaphosa announced on Sunday.

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READ | Covid vaccines were developed quickly: How do we know they won't cause any long-term health effects?

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