UK Study Reveals Impact of Delaying Second Pfizer-BioNTech COVID-19 Vaccine Dose on Immune Response

Among countries that have implemented large-scale COVID-19 vaccination campaigns, the United Kingdom is one of those with a relatively high national vaccination rate. According to statistics from Our World in Data, as of May 12, 52.9% of the UK population had received at least one dose of a COVID-19 vaccine. Early in the vaccination rollout, the UK adopted a strategy of prioritizing first doses for as many people as possible, rather than ensuring that individuals received their second dose within the conventional 3- to 4-week interval. Currently, only 27.8% of the UK population has completed the two-dose regimen. So, what impact does extending the interval between the two vaccine doses have on the human immune response?

Recently, a joint study conducted by the University of Birmingham and Public Health England (PHE) found that among individuals aged 80 and above, extending the interval between the two doses of the mRNA vaccine co-developed by Pfizer and BioNTech from 3 weeks to 12 weeks resulted in a 3.5-fold increase in the levels of specific antibodies against the SARS-CoV-2 spike protein in recipients. The renowned scientific journal *Nature* has also reported on this study.

In this study, 99 participants aged 80 years and older received two doses of an mRNA COVID-19 vaccine at a 3-week interval, while 73 participants received two doses of the same vaccine at a 12-week interval. Three weeks after administration of the second dose, researchers measured the levels of spike protein-specific antibodies in their blood. The results indicated that the specific antibody level in the 12-week interval group was 4,030 U/mL, approximately 3.5 times higher than that in the 3-week interval group (1,138 U/mL).

Researchers also assessed the cellular immune responses of vaccine recipients, which play a crucial role in facilitating and sustaining antibody production. The results showed that in the 3-week interval group, 60% of recipients developed a confirmed cellular immune response 2–3 weeks after receiving the second dose. In the 12-week interval group, however, only 31% of recipients exhibited a confirmed cellular immune response 2–3 weeks following the second dose. Further research is still required to investigate the reasons behind these discrepancies between the cellular and antibody-mediated immune responses.

This study is currently posted on a preprint server and has not yet undergone peer review.

Dr. Helen Parry, first author of the study from the University of Birmingham, said: "This is the first study to examine the antibody and cellular immune responses resulting from extending the interval to the second vaccine dose. Our research shows that among older adults with the interval extended to 12 weeks, peak antibody levels following administration of the Pfizer/BioNTech COVID-19 vaccine were significantly elevated."

In the UK, extending the interval between the two vaccine doses has yielded favorable real-world outcomes. However, Dr. Stephen Griffin, a virologist at the University of Leeds, noted that the country's public health measures also played a contributing role. "Theoretically, individuals remain susceptible to infection between the first and second doses," he said. "The UK maintained social distancing restrictions even as it expanded its vaccination campaign."

Dr. Alejandro Cravioto of the World Health Organization’s Strategic Advisory Group of Experts on Immunization (SAGE) stated that the study findings are good news; however, they specifically pertain to the vaccine jointly developed by Pfizer and BioNTech. Countries must consider the current status of locally circulating viral variants, as well as whether administering only a single dose could increase the risk of infection.

A study recently published in the journal *Science* also found that the practice of allocating limited vaccine supplies to prioritize first doses for a larger population can reduce the short-term COVID-19 infection rate; however, in the long run, administering only a single dose may promote viral mutation. Therefore, receiving the second dose as soon as possible can best prevent these long-term risks from becoming an unfortunate reality.

No one is safe until everyone is safe. If you have not yet been vaccinated, consider scheduling it as soon as possible to do your part in helping the world return to normalcy sooner.

References:

[1] Delaying second Pfizer vaccines to 12 weeks significantly increases antibody responses in older people, finds study. Retrieved May 14, 2021, form https://www.birmingham.ac.uk/news/latest/2021/05/covid-pfizer-vaccination-interval-antibody-response.aspx

[2] Delaying a COVID vaccine’s second dose boosts immune response. Retrieved May 14, 2021, from https://www.nature.com/articles/d41586-021-01299-y

▽Follow 【WuXi KanGermany】WeChat Official Account