If you are handling your health wisely, then you are vaccinated against SARS-CoV2, the virus that causes COVID-19. This means all three doses of one of the mRNA vaccines (Pfizer-BioNTech or Moderna), or, if your first shot was a viral vector vaccine, especially the single dose Janssen, the following dose should be an mRNA vaccine, in most cases. Rather than thinking of the new jab as a “booster”, you should consider it the third shot of the primary series. When it comes to children, boosters of the Pfizer-BioNTech vaccine are now approved in the United States and several other countries for ages 12 years and up, effectively expanding the primary series to three jabs, occurring over a period of 6 months. This means three weeks, or a little more, between dose 1 and dose 2, then at least 5 months between dose 2 and dose 3. In many cases, such as with 12-15 year olds who received their first two doses soon after they were approved during the spring of 2021, the time between dose 2 and dose 3 will end up being 7 months or longer. Meanwhile, a COVID-19 vaccine is not yet available for children below the age of 5 years. Researchers are working on it, but it is delayed on account of issues of dosing and numbers of shots, as we will discuss below.
As of the writing of this post in January, 2022, the Pfizer-BioNTech vaccine is the only COVID-19 vaccine approved for people below the age of 18 years. In adults and children ages 12 years and up, the dose is 30 micrograms (μg) per shot. Children ages 5 through 11 years, however, receive one third of the adult dose, meaning 10 μg per shot. Currently, the primary series for the 5-11 year age group consists of two shots, separated by at least 21 days. No booster/3rd dose has yet been authorized for ages 5-11, while those ages 12-15 are just now getting their 3rd dose, meaning another adult 30 microgram dose. When it comes children ages 6 months to just under 5 years, the dose that is in the final stages of clinical testing is 3 μg, meaning one tenth of the adult dose and 30 percent of the age 5-11 dose. While the safety data are good for this 3 μg dose in children below age 5, the effectiveness has been disappointing when the primary series consists of just two doses.
In comparison, two shots of the 10 μg dose in children ages 5-11 produce an excellent immune response, as do two shots of the 30 μg dose in children ages 12 and up (although, the third dose further improves the benefit in this latter group when given at least 5 months after the second dose). Consequently, the researchers and health officials have suggested that the primary series for children under the age of 5 years may need to consist of three shots of the 3 μg dose. The need to evaluate such a three-dose primary series has increased the amount of time needed for the clinical trials. Consequently, it will take longer than previously anticipated for the 3 μg dose vaccine to be ready for emergency use authorization. However, given a growing consensus that the third dose should be considered part of the primary series (rather than a booster) in adults and older children, the idea that the young child vaccine may start out as a three-dose primary series should not be surprising.
Now there is an issue that has been blown out of proportion, due to misinformation and vaccine hesitant people and antivaxxers misconstruing it, but you may be concerned if you have children or teens in the 12 years and older group. This is the issue of a pair of very rare adverse effects called myocarditis and pericarditis, or myopericarditis when they occur together. It has not been an issue at all for the children ages 11 and younger, receiving the 10 μg dose. However, in the 12-39 year age group, myopericarditis/myocarditis have been reported at rates of 12.6 to 14 cases per 1 million recipients of the adult dosage, mostly adolescent and young adult males. 12.6 to 14 cases per million equates to the risk of being hit by lightning once during a period of 15-20 years, but the reports have raised concern, since younger people have been at lower risk of developing severe cases of COVID-19 in the first place.
Since the early data were showing the already low risk being higher after the second dose than than after the first, there were some ideas discussed about giving just one dose to teens and children, especially males, if they had no health conditions putting them at risk for severe COVID-19, such as obesity. But, as an increasing number of adults received third doses, the conversation shifted to prospect of limiting children to two doses. However, data from Israel now suggest something very interesting —that the myocarditis/myopericarditis risk actually drops after the third dose compared with the second dose. This means that the optimal balance between effectiveness versus risk of adverse effects turns out to line up with a three dose primary series, not only in people ages 12-39, but also in the age 5-11 year group, with its lower dose. The bottom line is that you’ll probably see approval for third shots for children ages 5-11, and then, albeit after more waiting, a three-shot primary series of the microdose shot for the early childhood ages.