On June 17, 2022 the FDA authorized the Pfizer-Biontech and Moderna COVID-19 vaccines for children aged 6 months to 4 years old. Shortly after on June 18 the CDC also gave the green light to give these vaccines to children in this age group. This is now the fourth time the FDA and CDC have met to review data on the COVID-19 vaccines in different age groups, with the vaccines getting authorized after each meeting. Many people may still be wondering about what kinds of data they review in these meetings or how they tell that the vaccines are safe and effective enough to give to children. For this reason, this week’s article focuses on a clinical trial in which the Pfizer vaccine was tested for safety and effectiveness in children ages 5 to 11. While the studies looking at the vaccines in children 6 months to 4 years old are still being published, this study is of the same design and can give us an idea of what each of the vaccine studies for children look like.

The study began by signing up children and their families who agreed to participate. The children were from the US, Spain, Poland, and Finland, though most of the children (70%) were from the US. The researchers made sure to gather children that matched the racial and ethnic breakdown of each country’s population, and also had a 50/50 split of boys and girls. In total, 2,268 children participated in this study. The study began in June 2021 and ended in September 2021.

In this study children were chosen at random to be in one group that received the vaccine for COVID-19 and another group that did not get the vaccine. 1,517 were given the Pfizer vaccine (two doses 21 days apart) and 751 children were just given an injection of saline (purified salt water). This allows the researchers to see how well the vaccine works by looking at differences between the group that got the vaccine and the group that did not. In this study, the researchers looked at differences between the two groups in the amount of COVID-19 cases that emerged, the amount of antibodies for the COVID-19 virus that the children had, and the presence of side effects.

The researchers compared the amount of COVID-19 cases that emerged in the vaccinated children and unvaccinated children to get a sense of how well the Pfizer vaccine works at reducing cases of COVID-19. They found that by the end of the study the amount of vaccinated children that got COVID-19 was about 10 times lower than the amount of unvaccinated children that got COVID-19. This shows that the vaccine worked quite well at reducing the risk of COVID-19 in children. The researchers also found that the levels of antibodies for the COVID-19 virus in the children who got the vaccine were close to the levels of antibodies in 16 to 25-year-olds who received the Pfizer vaccine in an earlier study. Almost all (99.2%) of the vaccinated children showed an increase in antibodies that was strong enough to fight the virus – another sign that the vaccine was doing its job. As expected, the children who did not get the vaccine did not have antibodies for the COVID-19 virus. It’s important to note that when the researchers looked at the antibody levels, they looked only at the children who had not yet been infected with COVID-19, which was the majority of children in the study (91%). The researchers did this to make sure that any antibodies they found were from the vaccine and not just from a previous COVID-19 infection.

To test whether the vaccine was safe for children, the researchers watched for any side effects. Parents of the children who participated in the study were asked to keep an electronic diary of any side effects that their children had for 7 days after each dose of the vaccine. Reports on any serious side effects were collected for 6 months after the second dose of the vaccine, including a 1-month follow-up visit. The researchers found that the majority of side effects were mild or moderate and went away within 2 days. Common side effects of the vaccine were headache and fatigue. Less than 1% of the children who got the vaccine experienced severe side effects like high fever or swollen lymph nodes, which still went away on their own. Only 1 child who got the vaccine required medical attention for a high fever of 104 degrees, which got better as soon as it was treated. No other side effects or health problems related to the vaccine were found at the 1-month follow-up visit or by the end of the 6-month period. This led the researchers and the FDA to conclude that the vaccine was safe for children ages 5 to 11.

If you or your child need to get vaccinated against COVID-19 or receive a booster dose visit COVID-19 Vaccination Information to find a vaccination location.

Antibodies – Antibodies are something that your body’s immune system makes to fight off a virus. They cover the virus so that it cannot multiply or cause any more damage to your body.

Chosen at Random – Chosen at random means that you use chance to choose something. For example, if you want to choose something at random you might flip a coin. You can imagine that the researchers in this study could have flipped a coin to choose which people get the vaccine – if the coin lands on heads then you get put in the group that gets the vaccine and if the coin lands on tails you go in the group that does not get the vaccine.

Racial and Ethnic Breakdown – A racial and ethnic breakdown of a country is how many people of different races and ethnicities are in a country. When the researchers say they matched the racial and ethnic breakdown of each country, it means that they collected an amount of children of each race and ethnicity that was similar to the amount of people of each race and ethnicity throughout the country. For example, if the US population is 20% Hispanic, the researchers made sure that 20% of the children they signed up were Hispanic.

Walter, E. B., Talaat, K. R., Sabharwal, C., Gurtman, A., Lockhart, S., Paulsen, G. C., ... & Gruber, W. C. (2022). Evaluation of the BNT162b2 Covid-19 vaccine in children 5 to 11 years of age. New England Journal of Medicine, 386(1), 35-46.