Why are Covid-19 vaccines for children taking longer than for adults?

Buzz

Ngày cập nhật gần nhất: 15/4/2026

While most adults have already completed their first and second doses, the vaccination campaign for children and teens is just beginning. The delay in vaccination timing is due to differences in the immune systems of children, which require separate testing processes.

Currently, the FDA has authorized Covid-19 vaccines for children aged 5 to 11, with Moderna possibly following a few weeks later. Moreover, Pfizer is preparing data to potentially vaccinate infants from 6 months to 5 years old.

The immune system of children under 12 operates differently compared to ours. As Genevieve Fouda, a researcher at Duke University, puts it, 'Children are not simply scaled-down versions of adults.' Researchers point out that the immune system also explains why children are less likely to develop severe cases of Covid-19.

Essentially, the immune system in young children is innate, whereas in adults, it's adaptive, relying on antibodies and T cells to combat viruses. The innate immune system (akin to an outer barrier) helps young children prevent new viruses from entering the body. This is crucial because in most severe Covid cases in adults, the innate immune system reacts slowly to the virus. To put it simply, adults fall ill because their immune system has to deal with a virus that has already infiltrated, whereas young children can stop the virus at the outer walls.

According to data from the FDA, over half of the children hospitalized for Covid had underlying conditions. This also explains why children are less likely to die from Covid; it's because their young age means they haven't accumulated as many underlying conditions as adults. Therefore, vaccines for children serve a different role than for adults; they help protect the vulnerable. That's why FDA experts are discussing whether to administer vaccines to children with severe health conditions only.

Now that we understand the immune system of children, the focus shifts to safety. FDA experts believe that if the risk of Covid infection in children is lower than in adults, the potential risks from vaccination may outweigh its benefits.

Testing vaccines on children also began with small doses (for example, Pfizer's 1/3 dose for 5-11 year olds) to determine the antibody response for each dosage and minimize side effects. Testing smaller doses partly explains why vaccine trials for children take longer, along with other factors such as recruiting child volunteers, which is more challenging. Parents are concerned about side effects and reluctant to have their children participate in trials, hence Moderna only had about 7,000 child volunteers compared to 30,000 adults.

Unlike adults, where trials focus on finding infections (and trials with adults already know the vaccine's effects), trials with children primarily aim to detect safety issues, even unrelated to the vaccine. For example, there were cases of children testing Pfizer's vaccine then swallowing a coin. Ultimately, most clinical trials start with adults, except for diseases that only appear in young children, until safety is established before testing on young children.

Source: Popsci

Image: The Washington Post

Mytour's content is for customer care and travel encouragement only, and we are not responsible.

For errors or inappropriate content, please contact us at: [email protected]