Covid-19 vaccine for children is no different than that for adults

Since May, the US and many countries around the world have begun vaccinating adolescents (aged 12 to 17) with the Pfizer vaccine, under an emergency approval program. On October 7, Pfizer filed an application with the US Food and Drug Administration (FDA) for a vaccine license for a younger group, aged 5 to 11.

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Group from 12 to 17 years old,Pfizer vaccine schedule is equivalent to that for adults:two doses of 30 micrograms three weeks apart, according to the FDA. Most vaccines use the same adult dose for children, except for hepatitis B (which requires a higher dose for adults) or tetanus, diphtheria, and pertussis (which requires a higher dose for children).

Unlike drugs, vaccines do not usually have higher doses prescribed for the elderly or seriously ill, because they are used in healthy people.

"Vaccines work in a unique way. They don't stay in the blood at a certain concentration (like a drug), but they stimulate the immune system. The human immune system will react to any foreign invader, even in very small amounts," explains Dr. Amesh Adalja, a senior scholar in the Johns Hopkins Center for Health Security. "So the vaccine dose and the body's response are often not correlated. The challenge is finding the right dose to stimulate the immune system. For most vaccines, one dose is enough for most people," he adds.

In other words, the vaccine itself is not transported through the body like a drug. Its mechanism is to instruct immune cells to recognize the pathogen and respond later. Therefore, the vaccine dose is mostly the same for many weight groups. Scientists often try to find the lowest dose of vaccine that is still safe and effective enough to protect the body. This is also the reason why experts recommend that the community should not let children delay or avoid vaccination, even if they are stunted or obese. nCoV is very small, 60-140 nanometers in size, but just a tiny amount of virus can make a person sick. "Vaccines have the same mechanism," said Dr. Adalja. "Because the immune system is developed enough to respond to small amounts of foreign virus, for most vaccines, people of different weights are given the same dose."

Pfizer announced in March that its vaccine reduced the risk of nCoV infection by 100% in children aged 12 to 15, and by 95% in people aged 16 to 25.

For the 5 to 11 year age group, the dosage is different.Although one dose of the vaccine is used for most of the population, scientists assert that "children are not miniature adults." The Pfizer vaccine is given to children at a lower dose of only 10 micrograms, has minimal side effects and can be given together with the flu vaccine.

Children have different immune systems than adults. So Pfizer tested a lower dose (10 micrograms) in children aged 5-11, instead of the 30 micrograms used in adults. Scientists found that children still had a strong immune response even with the lower dose.

In fact, the dose is even appropriate for adults, according to Dr. Robert Frenck, who is leading the vaccine trial at Cincinnati Children’s Hospital. This is consistent with previous findings that smaller doses of the vaccine may be more effective in heavier people.

"We tested 10 micrograms, 20 micrograms and 30 micrograms in adults and found that in the 18-55 age group, even 10 micrograms gave a very good immune response," he said. "But people 65 and older did not respond to the lower dose. That's why we chose to give 30 micrograms in general adulthood."

The dose is effective in the elderly and well tolerated in the young. Given the limited time available, scientists believe this is the optimal choice.

Dr Frenck said the 10-microgram dose of the vaccine was also effective in children aged 12 to 18. For the youngest group, children under 5, scientists are testing a 3-microgram dose.

Lower doses also help reduce vaccine side effects to a minimum.

"Side effects in children are the same as in adults," Frenck said. "The most common is pain at the injection site, but headaches and fatigue are also common. Fever and chills are less common, occurring in about 10 to 11 percent of children. As in adults, side effects in children last a day or two, after which they return to normal."

Many parents are concerned about myocarditis, an inflammation of the heart muscle that has been reported in people who have received the Moderna and Pfizer vaccines. Dr. Frenck said this is a rare side effect, occurring in a few cases per 100,000 people. "That means 99.999% of people will not experience this symptom. Most of these are seen in adolescent males, they are mild, can be treated with Motrin (ibuprofen), and all recover," he added.

Dr. Frenck noted that children who received the Pfizer vaccine did not experience the blood clotting or thrombocytopenia side effects seen with the Johnson & Johnson or AstraZeneca vaccines.

"In addition to clinical trials, we have given hundreds of millions of doses of vaccine to adults and adolescents. If there are no problems after hundreds of millions of doses, there will be no problems with children. Parents do not need to worry because the vaccine has been widely administered, and hundreds of millions of people are safe," he said.

Experts say vaccinating children is the goal in controlling the pandemic in this new phase. Although children and adolescents have mild symptoms and are less likely to be hospitalized than adults, they can still become seriously ill quickly.