Pfizer COVID-19 Vaccine Trial Results: Stellar Efficacies in Children and Against Variants

Pfizer released new COVID-19 vaccine trial results this week from its ongoing clinical studies, which include data showing that its COVID-19 mRNA vaccine is 100 percent effective in children between the ages of 12 and 15 and has a 91 percent efficacy against variants with protection lasting at least six months.

The highly awaited COVID-19 vaccine trial results address what have been three highly contested areas of concern: is the COVID-19 vaccine safe for kids, is it effective against some of the new variants of SARS-CoV-2 and how long will immunity last?

With overwhelming positive answers and results for these questions, the Pfizer/BioNTech COVID-19 vaccine may be on its way to becoming one of the first vaccines to be approved/authorized for children. And with variants of concern taking a stronghold in many places around the world, the demonstrated efficacy of the vaccine against variants, including the concerning B.1.351, offers much-needed reassurance, as does its durability over a period of at least six months.

Pfizer’s newest and updated COVID-19 vaccine trial results from its ongoing Phase III clinical trial confirms that protection lasts at least six months after administration of the second dose.

How Safe and Effective is Pfizer’s COVID-19 Vaccine for Kids?

In a pivotal Phase III trial involving adolescents 12 to 15 years of age, Pfizer/BioNTech’s COVID-19 vaccine trial results show that its vaccine, BNT162b2, has a demonstrated efficacy of 100 percent and elicits strong antibody responses. These responses were stronger than those reported in a trial of 16- to 25-year-old participants that received the vaccine. The vaccine was well-tolerated in both age groups.

The trial involved 2,260 adolescents 12 to 15 years of age in the US. In the trial, 18 cases of COVID-19 were observed in the placebo group versus none in the vaccinated group. The vaccine demonstrated high immunogenicity, with generation of high SARS-CoV-2-neutralizing antibody titers in a subset of adolescents one month after the second dose. This was comparable, and even higher, than titers observed in participants aged 16 to 25 years old from a previous analysis. Side effects were generally consistent with those seen in the 16 to 25 years of age group.

Pfizer and German partner BioNTech are preparing to promptly submit the updated COVID-19 vaccine trial results to the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) to request expansion of the Emergency Use Authorization (EUA) and EU Conditional Marketing Authorization for BNT162b2.

“We share the urgency to expand the authorization of our vaccine to use in younger populations and are encouraged by the clinical trial data from adolescents between the ages of 12 and 15,” said Albert Bourla, chairman and chief executive officer, Pfizer in a press release from the company. “We plan to submit these data to FDA as a proposed amendment to our Emergency Use Authorization in the coming weeks and to other regulators around the world, with the hope of starting to vaccinate this age group before the start of the next school year.”

The companies also provided an update on COVID-19 vaccine trial results related to a Phase I/II/III study of BNT162b2 in children between the ages of six months and 11 years. The first children were dosed in the global trial in late March in which the safety, tolerability and immunogenicity of the vaccine is being evaluated on a two-dose schedule (given 21 days apart) in three age groups: children aged five to 11 years, two to five years and six months to two years. The companies revealed that the five- to 11-year-old cohort was dosed last week and the two to five-year-old cohort will begin to be dosed next week.

How Does the Vaccine Fare Against Variants and How Long Does Protection Last?

In COVID-19 vaccine trial results from another topline study, Pfizer announced yesterday that BNT162b2 demonstrated a high efficacy of 91.3 percent against COVID-19, achieved seven days after the second dose and which lasts up to six months thereafter. Encouragingly, the vaccine demonstrated 100 percent efficacy in the prevention of COVID-19 in trials in South Africa where the B.1.351 variant is rampant.

The vaccine was observed to be 100 percent effective in preventing severe disease as defined by the US Centers for Disease Control and Prevention (CDC) and 95.3 percent effective in preventing severe disease as defined by the FDA.

The latest COVID-19 vaccine trial results were obtained from an analysis conducted on 927 confirmed symptomatic cases of COVID-19 from the large-scale Phase III trial, which currently has 46,307 participants. Of the 927 COVID-19 cases evaluated, 850 cases were in the placebo group and 77 were in the vaccine group, translating to a vaccine efficacy of 91.3 percent. Pfizer says these results “build upon and confirm previously released data and demonstrate strong protection against COVID-19 through six months post-second dose.”

Importantly, 32 cases of severe disease, as defined by the CDC, were observed in the placebo group versus none in the vaccinated group, demonstrating the 100 percent efficacy of the vaccine against severe disease. As per the FDA’s definition of severe disease, 21 severe cases were found in the placebo group compared with one case in the vaccinated group, resulting in an efficacy of 95.3 percent.

Pfizer says, “efficacy was generally consistent across age, gender, race and ethnicity demographics, and across participants with a variety of underlying conditions.”

Furthermore, COVID-19 vaccine trial results from South Africa, where the B.1.351 lineage is widespread and dominant, were also shared by Pfizer. In the analysis, among 800 participants, nine cases of COVID-19 were observed and they were all in the placebo group, resulting in a vaccine efficacy of 100 percent. The nine cases were sequenced in an exploratory analysis, and six of the nine were confirmed to be of the B.1.351 lineage. This clinical data supports previous in vitro immunogenicity data showing that that BNT162b2 induces a robust neutralizing antibody response to the B1.351 variant. Despite those initial lab studies showing a lower response compared to the parental wild-type strain, Pfizer says these clinical results show that it doesn’t appear to affect the high observed efficacy against this variant.

“These data confirm the favorable efficacy and safety profile of our vaccine and position us to submit a Biologics License Application to the US FDA,” said Bourla in a press release from Pfizer. “The high vaccine efficacy observed through up to six months following a second dose and against the variant prevalent in South Africa provides further confidence in our vaccine’s overall effectiveness.”

Pfizer/BioNTech’s vaccine has been evaluated for safety in more than 44,000 participants 16 years of age and older now, with more than 12,000 vaccinated participants having at least six months follow-up after their second dose, according to Pfizer.

The companies began trials to evaluate efficacy against variants in early March.

Pfizer and BioNTech will be sharing their latest COVID-19 vaccine trial results with global regulatory agencies soon. The rolling in of this data is promising as it helps address the vaccination of children, which will be key in mitigating community transmission. It also helps shed light on the effectiveness against the concerning B.1.351 variant, which may have the potential to evade the immune response. Based on the trial results, this does not appear to compromise the efficacy of Pfizer/BioNTech’s vaccine, which is welcome news amidst its growing circulation.