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Results announced by Pfizer-BioNTech on a phase 3 trial of their COVID-19 vaccine in adolescents

Update

Pfizer have published a press release announcing positive topline results of their phase 3 trial of the Pfizer-BioNTech COVID-19 vaccine in adolescents 12 to 15 years of age.

This article was published on
March 31, 2021

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Media Release

Expert Comments: 

Dr Stephen Griffin

In short, this is fantastic news. Demonstrating efficacy and safety in younger patients is an important step forwards in terms of enabling eventual population immunity against SARS-CoV2. It will enable a long term programme of school-based vaccination to be implemented following the initial rollout, ensuring that our population is well protected from the virus in the future. It will also be important to alleviate the concerns of parents and teachers alike regarding the spread of infection within schools, and is by far and away more preferable than mass testing and mitigation measures in the longer term.

Dr Peter English

Please note my previous comments on the vaccination of children at SMC, in which I focus on the importance of vaccinating children and young people if we are to achieve “herd immunity” by getting and keeping the Rt value below 1 through vaccination.1

As with most such press releases, details are scanty, making it hard to comment confidently on the validity of the claims made. It would be very helpful to see the full details in one or more peer-reviewed papers.

This press release tells us that there are now good data to demonstrate that the Pfizer-BioNTech vaccine is safe and effective in adolescents 12 to 15 years of age.2 The study of 2,260 recipients found 18 cases of Covid-19 in the unvaccinated group, and none in the vaccinated group. It also showed a robust immune response in vitro (antibody responses).

The press release does not tell us how cases were identified, or the cases’ severity. It would be interesting to know if the study cohorts underwent regular screening for asymptomatic infection, and if so, how this was done. It would be useful to know how effective the vaccine is at preventing asymptomatic infection. Young people are less likely to have severe disease; and when they are infected, they are more likely to have asymptomatic infection, allowing them to transmit the disease to others.

The press release does not mention whether there was any testing of cellular (eg T cell) immune responses. We know that these are also important both in preventing disease in vaccine recipients, and in preventing infection and onward transmission.

The press release tells us that the vaccine, in this 12-15 year age group, “was well tolerated, with side effects generally consistent with those observed in participants 16 to 25 years of age”. This is important: safety is a serious concern when introducing a new vaccine. Given that the vaccine is safe in other age groups, we should not expect problems in this age group. The study size was not large when looking for uncommon side effects; but it may have been sufficient. Again, we’d want to see more details.

The press release does not tell us whether the participants were likely to have been exposed to any of the variants that have caused concern. It would be reassuring to know that the vaccine was equally effective against all variants.

The press release also refers to trials in younger age groups (in children 6 months to 11 years old). It contains no data on such trials.

Unlike Johnson and Johnson/Janssen trials, Pfizer does not appear to have tested any different prime-boost intervals. Given that everything we know about vaccines tells us that longer prime-boost intervals are more effective and, particularly given that the risk to children and young people from disease is so much lower than at older ages, so extending the period would cause little if any harm (and is likely to enhance their eventual response), this seems a missed opportunity.

Adolescence – that period when young people’s bodies transition from child to adulthood – is a period in which some diseases emerge; and some of these diseases are uncommon and poorly understood. We have seen previous vaccine scares when uncommon conditions in adolescence have been linked to vaccination. Nearly always, the association has turned out to be coincidence, rather than being caused or made more common by the vaccine; but it is very likely that similar concerns will be raised with Covid-19 vaccines when they are introduced in this age group, only to be settled when further investigations prove them to be mere coincidence.

We must be prepared for such scares, and not overreact to them.3 4

Thankfully, research done related to other vaccines given in adolescents – such as the human papillomavirus (HPV) vaccine have helped clarify the background rates of unusual conditions in this age group, which will make it easier to be clear, earlier on, whether we are seeing more such events than we would normally expect. 5

When the full, peer-reviewed papers appear – or when regulators receive the data directly from the companies – it will open up the way to extending vaccination to this age group (and likely to the younger age group referred to in the press release). It will be important to do this to achieve herd immunity.1 6”

References

  1. English PMB, Faust S. Expert comments on the use of COVID-19 vaccines in children. Science Media Centre 2021; Updated 24 Mar 2021; Accessed: 2021 (24 Mar): (https://www.sciencemediacentre.org/expert-comments-on-the-use-of-covid-19-vaccines-in-children/).
  2. Pfizer Press Office. Pfizer-BioNTech Announce Positive Topline Results of Pivotal COVID-19 Vaccine Study in Adolescents. Pfizer News 2021; Updated 31 Mar 2021; Accessed: 2021 (31 Mar): (https://www.pfizer.com/news/press-release/press-release-detail/pfizer-biontech-announce-positive-topline-results-pivotal).
  3. Larson HJ. The biggest pandemic risk? Viral misinformation. Nature 2018;562:309. (https://www.nature.com/articles/d41586-018-07034-4).
  4. Vaccines Today Editors. HPV vaccines and #fake news. Vaccines Today 2018; Updated 27 Apr 2018; Accessed: 2018 (09 May): (https://www.vaccinestoday.eu/stories/hpv-vaccines-and-fake-news/).
  5. Siegrist C-A, Lewis E, Eskola J, Evans S, Black S. Predicting vaccine scares following HPV immunization: A cohort study to define risks of coincidental associations with autoimmune diseases. European Society for Infectious Diseases. Porto, Portugal: Kenes, 2007(www.kenes.com/espid).
  6. Mandavilli A. The Pfizer-BioNTech Vaccine Is Said to Be Powerfully Protective in Adolescent. New York Times 2021; Updated 31 Mar 2021; Accessed: 2021 (31 Mar): (https://www.nytimes.com/2021/03/31/health/pfizer-biontech-vaccine-adolescents.html).

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