Here's what you should know about the COVID vaccine for kids under 5

The first COVID-19 vaccine for children under the age of five has (finally!) been approved by Health Canada. Moderna’s vaccine, known as Spikevax, will now be available for babies, toddlers and preschoolers. With BA.4 and BA.5 variants on the rise, we answer parents' most common questions about the under-5 vaccine.

1. What do we know about the recently approved Moderna COVID-19 vaccine?

Moderna’s vaccine uses messenger RNA (mRNA) technology, which teaches cells how to make a protein to trigger an immune response, and it’s a little-kid version of the vaccines already approved for older age groups.

The Moderna vaccine is a two-dose series for children aged six months to five years old. Each shot consists of 25 micrograms per shot, a quarter of the dosage approved for 18 plus. (The adult version of the vaccine is 100 micrograms and the version for six to 11-year-olds is 50 micrograms).

While the doses in the clinical trials were given four weeks apart, the National Advisory Committee on Immunization (NACI), which provides recommendations for vaccine usage in Canada, advises waiting at least eight weeks between the first and second dose. (Kids who are immunocompromised may be eligible for three doses, spaced four to eight weeks apart.) That longer interval allows for kids to mount a better immune response, explains Jesse Papenburg, a paediatric infectious disease specialist at the McGill University Health Centre.

2. Why did the COVID-19 vaccine for the youngest kids take the longest?

“All these vaccine trials and submissions go through the same high-level vigorous process,” says Anne Pham-Huy, a paediatric physician and infectious disease specialist at the Children’s Hospital of Eastern Ontario, who is also a member of the National Advisory Committee on Immunization (NACI).

“When we approve paediatric vaccines, we have to make sure they are safe. That’s our number one priority,” says Sabina Vohra-Miller, a health advocate and founder of Unambiguous Science. This is why vaccines were tested and approved in a phased way, starting with the oldest group, down to the youngest, she explains.

Manufacturers also wanted scientists to study the lowest dose possible for kids that could mount a satisfactory immune response, explains Papenburg. “When we have lower doses that typically translates into less adverse effects,” he explains. And before giving it to children, “we have real-world evidence with millions of doses given in North America.” (Plus, in late June, the U.S. Food and Drug Administration authorized the emergency use of Moderna and Pfizer- COVID vaccines for kids 6 months and up, so there’s already thousands of vaccinated kids south of the border.)

3. What are the potential risks or side effects of the COVID vaccine for kids under 5?

In the Moderna trial, side effects of the vaccine were similar to those of other routine vaccines, including arm pain, fever, muscle pain, headaches, nausea and tiredness. In adults and adolescents, the mRNA vaccines can come with a small risk of myocarditis and pericarditis (inflammation of the heart muscle and heart’s outer lining) but cases are extremely rare. In the safety information released from Moderna, no cases were reported in their under-six vaccine trial, says Vohra-Miller.

4. Is the vaccine effective against new COVID-19 variants? 

The vaccine was developed for the original SARS-CoV-2 virus and as we know, the virus has mutated several times since then.

In the Moderna trial, antibodies produced in this youngest age group were similar to adults or slightly higher, but when it came to symptomatic infections—so, actually getting sick from the virus—the data wasn’t as strong, explains Vohra-Miller.

Vaccine efficacy against symptomatic illness was 51 percent for kids six months to two years and 37 percent for two to six-year-olds. These were similar to efficacy estimates in adults against Omicron after two doses of the adult Moderna vaccine.

However, Pham-Huy stresses that even if the vaccine is less effective against infection, it still plays a critical role. “The main goal is to prevent severe disease and you do prevent severe disease with these vaccines,” she says. If your child’s body mounts an antibody response to the original strain thanks to the vaccine, their body will recognize that spike protein and make antibodies. Over time, those antibodies go down, which is normal. But the immune system matures, evolves and refines itself, so even though the variants can evade the immune system and cause infection, your child is still ultimately protected against severe disease from subsequent variants, Pham-Huy explains.

5. My child had COVID not too long ago. Should they still get the vaccine?

“So many kids have had COVID since Omicron emerged,” says Papenburg, citing studies that estimate 30 percent or more of kids have been infected with COVID in this past wave. But that doesn’t mean they shouldn’t get vaccinated.

“We know infection does convey some degree of protection against severe outcomes,” he says. But the duration of protection against subsequent infection is quite low (especially with all the new variants) and it’s incomplete, he explains. Studies have shown that the combination of infection and vaccination offers the highest degree of robust and longest-acting immune response, says Papenburg.

6. How long after having COVID can my kid get the vaccine?

NACI recommends parents wait eight weeks between a COVID infection and getting their child their first or second dose of the vaccine. “It allows for the immune system to absorb the information it got from the infection so it's better equipped to respond to the vaccine and mount an immune response,” says Papenburg. Keep in mind that your child won’t have fulsome protection from the vaccine until 14 days after their last vaccination, states NACI.

7. What about Pfizer’s COVID-19 vaccine for kids under 5?

Pfizer’s vaccine, called Comirnaty, was initially two doses of 3 micrograms for children aged six months to five years. (The approved dose for five- to 11-year-olds is 10 micrograms, and for people 12 and up it’s 30 micrograms). However, in the trial, participants did not mount an adequate immune response to the vaccine, so the company extended the trial to include a third dose. This delayed the company’s submission to regulatory bodies, which was initially expected in February but was submitted for approval on June 23, 2022.

Pfizer is a three-dose regimen, so even when it’s approved, it will take longer to get full protection from the vaccinations, says Vohra-Miller.

8. What if your child is almost 5 years old? 

There are a few situations for five-year-olds that are addressed by NACI. Here’s what they recommend right now:

• For children who are five and haven’t had any COVID vaccinations yet, the Pfizer shot for 5 to 11-year-olds is still recommended. (There’s more data on Pfizer in this age group and it’s more widely available).
• If your child is under five and receives Moderna for their first dose, they should get the 25 microgram Moderna shot for their second dose, even if they’ve already turned five.
• If your child is five and has received a Moderna vaccine and turns six before their two doses are complete, ideally they should receive Moderna’s 6-11 vaccine, which is a slightly higher dosage, at 50 micrograms. (If they do end up mixing doses, which isn’t recommended, then it would still be considered a completed primary series.)

9. Can the COVID vaccine be given with other vaccines?

Babies, toddlers and preschoolers often have regular immunizations for diseases such as measles, mumps and rubella or chickenpox. But right now, NACI doesn’t advise getting any other vaccines at the same time as the COVID shot. The reason? They recommend waiting at least 14 days between vaccinations so there’s time to monitor for potential side effects from either shot, says Papenburg.

10. What do the experts say about vaccinating your baby, toddler or preschooler?

“If I had a child under five years old, there’s no doubt I would make sure they got their vaccine,” says Pham-Huy. “I’d expect them to catch COVID at some point but I’d rather not have them go through it without any kind of protection.”

“The vast majority of children hospitalized during Omicron were kids under five,” says Pham-Huy. Even though most kids don’t develop severe symptoms from COVID, “Infectious disease is unpredictable. You don’t know if your two-year-old will have a super easy, asymptomatic time with COVID or if they will end up in the hospital.”

And while it’s still being studied, it appears that vaccines reduce the risk of children developing multisystem inflammatory syndrome (MIS-C), a rare but dangerous condition that can occur after COVID infection. Plus, vaccination may help prevent long COVID in kids.

Families need to do an individual risk assessment to make a decision they are comfortable with and make sure they talk to a healthcare professional, recommends Papenburg.