How Covid-19 vaccines for children are different from vaccines for adults

Last week, vaccine maker Pfizer said tests showed its Covid-19 vaccine works well in children ages 5 to 11. The vaccines these younger kids could get would be the same as the shots teens and adults have received, but the dose will almost certainly be different.

Children have different immune systems from adults. Knowing this, Pfizer tested varying doses in its trials of children 5 to 11. Kids, it turns out, have a strong immune response even to lower doses. So children under 12 will likely be getting a 10-microgram dose of vaccine, compared with a 30-microgram dose for adults.

 

In fact, most adults could get by with lower doses, too, says Dr. Robert Frenck, director of the Vaccine Research Center at Cincinnati Children's Hospital.

 

"We found in 18-55-year-olds, a 10-microgram dose gives a very good immune response," Frenck said. "But the 65 and above, they did not respond as well to the lower doses, and so that's why we chose that 30-microgram dose, across the adult age range from 18 to above."

 

Frenck said there wasn't any time -- or any reason -- to finesse the dosing last year. "During a pandemic, we wanted to get a vaccine out quickly," he added.

 

Frenck said so far, the Pfizer vaccine appears very safe in younger children. "What we found is that the side effects in the children really mirrored exactly what we saw in adults," he said.

 

"So the most common thing is pain at the injection site. Also having headache, and maybe fatigue. Fevers and chills were unusual -- only around 10-11% of the children having those. Similar to the adults, or identical to the adults, is that side effects lasted a day or two and then people were back to normal,” Frenck added.