Moderna says vaccine for young children is safe, but efficacy is ‘complicated’

To swiftly extend eligibility of the vaccine beyond adults, the children’s trials were designed primarily to measure safety and whether the vaccines conjured the same levels of virus-fighting antibodies. When the trial of the Moderna vaccine started, success was defined as immune responses equivalent to what was reported among young adults in the pre-Omicron period.

The Moderna trial hit that benchmark in young children. But two doses have turned out to be far less effective against the highly transmissible Omicron variant in adults, and that also held true for children. While protection against infection in young children was about 40 per cent overall, it was slightly lower in children younger than 2 years of age.

Moderna says its two-dose pediatric coronavirus vaccine is safe in young children.Credit:Louise Kennerley

Because the children’s trial wasn’t designed primarily to measure vaccine effectiveness, there are wide statistical uncertainties about the findings on efficacy, but the company said its statistical analysis showed it was above zero.

There were no cases of serious illness or hospitalisations in the trial, which included close to 7000 children 6 months to 5-years-old, making it impossible to detect the vaccine’s possible protective effect against the worst outcomes.

Jacqueline Miller, Moderna’s senior vice president of infectious diseases, acknowledged it was more challenging to interpret the data than early in the pandemic but said the immune responses provoked in children were similar to adults – and so was their protection against the Omicron variant.


“We’re optimistic that we can bring the vaccine forward, hopefully reasonably quickly,” Miller said. She added that the company plans to test a booster dose in children, and is submitting a proposal to regulators to test that four months after children complete their initial series of two shots.

In sharp contrast to the easy path of the first vaccines, children’s vaccines have had stops and starts, missing projected timelines and sowing frustration, confusion and impatience among parents and paediatricians.

In December, Pfizer and BioNTech announced that in 2- to 4-year-olds, a two-dose regimen failed to muster an immune response equivalent to the one that protected young adults. The companies added a third shot – and months of waiting – to the trial.

Then, in an about-face in late January, federal officials indicated there could be a path forward for two doses of the Pfizer-BioNTech vaccine, a strategy intended to allow children to start building immunity as officials awaited data on a third dose. But then the FDA said no decision would be made till results on a third dose arrived.


The failure has led some experts to question whether the Pfizer-BioNTech dose is too low, but Pfizer scientists have said they chose the low dose for the youngest children because it caused fewer severe fevers.

The Moderna pediatric vaccine caused fevers above 100.4 degrees in about 1 in every 6 of the youngest children under 2 years old. Among the 2- to 5-year-olds, the rate of fevers was slightly lower. Fevers higher than 104 degrees were rare, reported in just a few children, according to the company. There were no cases of myocarditis or pericarditis, heart inflammation that rarely occurs after messenger RNA vaccination.

Moderna has faced delays with pediatric vaccines. Its vaccine is authorised only for people 18 and older in the US, while Pfizer’s shot has been authorised for children as young as 5 years old.

Moderna filed for authorisation in teenagers last June, but a regulatory decision has been delayed, in part because of concerns that Moderna’s higher dose may increase the risk of myocarditis in that age group. The company is evaluating the potential of a half-dose for those teens.

The company announced on Wednesday it would be submitting updated data in all young age groups and would seek authorisation in children 6 to 11-years-old, too. That is less likely to spark interest among families, because the Pfizer-BioNTech shot is already authorised for that age group.

Children have been spared the worst of the pandemic, suffering lower rates of severe illness and death than older adults. But their hospitalisation rates soared to the highest level of the pandemic during the winter Omicron surge, according to a recent study from the Centers for Disease Control and Prevention.

During the peak of the Omicron variant surge in January, children younger than 5 were hospitalised at five times the rate as during the peak of the delta surge in early September. There was also no reliable way to predict which young children would end up in the hospital, because nearly two-thirds of children who were hospitalised had no underlying medical conditions.

The Washington Post

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