Moderna reports early success with COVID vaccine in children under 6
Biotech company Moderna has announced the first interim data from a clinical trial testing its mRNA COVID-19 vaccine in children under the age of six. The results show similar antibody responses after two doses to those seen in adults. Moderna plans to apply for US Food and Drug Administration (FDA) emergency authorization very soon.
Moderna’s announcement is the first positive clinical trial data for a COVID-19 vaccine in children after Pfizer recently extended its pediatric trials to three doses following reports of weak immune responses to two doses. The Moderna data covers two cohorts of children: approximately 2,500 children aged between six months and two years, and 4,200 children aged between two and six.
The trial tested a 25 microgram mRNA dose in children under the age of six. This compared to 50 micrograms in the six to 12 year old group and 100 micrograms in those 12 and older.
Moderna reports two vaccine doses administered in the child cohorts, separated by 28 days, resulted in a neutralizing of antibody responses similar to what was seen after two doses in adult trials. The side effect profile was also consistent with those seen in older cohorts.
Mild fever was the most prominent side effect detected in the trial, seen in 14.6 percent of the two to six year cohort and 17 percent of six month to two year cohort. No other safety concerns were detected, including no cases of myocarditis and no cases of MIS-C, a multisystem inflammatory syndrome.
The trial was not set up to focus explicitly on efficacy at preventing infection, however, Moderna does calculate the two dose protocol reduced infections from Omicron by 37.5 percent in the two to six group and by 43.7 percent in the six month to two years group. These numbers are inarguably low, but efficacy is the same as what is currently seen in adults after two doses against Omicron according to Moderna.
All vaccine breakthrough infections detected in the trial were mild and there were no reports of severe disease, hospitalization or death. In terms of the vaccines preventing severe disease or death, Moderna said it cannot estimate efficacy due to a lack of data. Because those events are rarer in children than adults, the trial would have needed to enroll tens of thousands of children to determine those effects.
"We believe these latest results from the KidCOVE study are good news for parents of children under 6 years of age,” explained Moderna CEO Stéphane Bancel. “We now have clinical data on the performance of our vaccine from infants six months of age through older adults. Given the need for a vaccine against COVID-19 in infants and young children we are working with the U.S. FDA and regulators globally to submit these data as soon as possible.”
One question that arises from this preliminary data is whether these younger cohorts would benefit from a third vaccine dose, in much the same way researchers have discovered a third dose is crucial for effective protection against Omicron in adults. Moderna’s pediatric trial is ongoing, and will explore the effect of third doses in all young populations.
Pfizer, the other big player in the COVID-19 mRNA vaccine field, has skipped any attempt at FDA approval for a two dose vaccine in young children. Several months ago it revealed it was adding a third dose to its trial protocol after early data indicated two doses did not produce effective immune responses in children under the age of five.
It has been suggested that Pfizer’s conservative dosage choices may have limited the efficacy of its mRNA vaccine in children. Pfizer has always worked with much lower mRNA doses compared to Moderna.
Pfizer's adult vaccine works with 30 microgram doses, compared to Moderna’s 100 microgram doses. But in children aged five to 11, the dose is reduced to 10 micrograms. And in Pfizer's recent trials with children under the age of five it has been focusing on 3 microgram doses.
So while Pfizer seems to be working on finding the lowest mRNA dose that can produce an effective immune response, Moderna has been working at the other end of the spectrum, looking for the highest dose that can be tolerated with minimal side effects.
A study published last month found the efficacy of Pfizer’s mRNA vaccine in children aged five to 11 seems to be waning much faster than what is seen in 12 to 17 year olds. Experts commenting on the study hypothesize this discordance to be significantly influenced by dose differences between the two age groups.
Pfizer expects its interim third dose data for children under the age of five to arrive sometime in April. Moderna, on the other hand, will move immediately on an FDA application for its two dose protocol in all adolescent age groups from two months up. So parents of young children could possibly have access to a COVID-19 vaccine for their kids by the end of April or early May.