Lancet study looks at inactivated COVID-19 vaccine for children

Two doses of the inactivated novel coronavirus (COVID-19) vaccine, CoronaVac, manufactured by Sinovac, are safe and provoke a strong antibody response among 550 children and adolescents 3 to 17 years old, according to a new randomized controlled trial published in the journal The Lancet Infectious Diseases.

More than 96 percent of children and adolescents who received two doses of the developed antibodies against SARS-CoV-2, the virus that causes COVID-19. Most adverse reactions were mild or moderate, with pain at the injection site the most reported symptom.

The authors conducted a randomized, double-blind, controlled phase 1/2 clinical trial of CoronaVac in healthy children and adolescents aged 3 to 17 years old in Zanhuang County, China. Between October 31 and December 2, 2020, 72 participants were enrolled in phase 1, with 480 participants enrolled in phase 2 between December 12 and December 30, 2020. The vaccine, either 1.5μg or 3μg per dose, or a control was given by intramuscular injection in two doses, at day 0 and day 28. In studies involving adults ages 18 to 59 years and people ages 60 years and older, participants received two doses of 1.5μg, 3μg, or 6μg, with 3μg doses suggested for use in further research. 

Among the 550 participants who received at least one dose of vaccine or the control, adverse reactions within 28 days occurred in 56 (26 percent) of 219 participants in the 1.5μg group, 63 (29 percent) of 217 in the 3μg group, and 27 (24 percent) of 114 in the control group. Most adverse reactions were mild or moderate, with pain at the injection site (13 percent) being the most reported symptom. Only one serious adverse reaction, a case of pneumonia, was reported in the control group, however, this was unrelated to the COVID-19 vaccination.

In phase 1, 100 percent of participants in both the 1.5μg and 3μg groups generated antibodies against SARS-CoV-2. Stronger immune responses, determined by the amount of antibodies produced that can neutralize the virus, expressed as geometric mean titer (GMT) were detected among the 3μg group compared with the 1.5μg group (GMTs of 117 and 55, respectively).

In phase 2, 97 percent of participants in the 1.5μg group produced antibodies against SARS-CoV-2, compared with 100 percent in the 3μg group. Participants in the 3μg group again produced a stronger immune response that those in the 1.5μg group.

Similar to findings for other vaccines that increasing age is linked with reduced immune responses, the authors note that immune responses among children and adolescents were higher than those in adults aged 18 to 59 years and elderly aged 60 years and older.

No significant differences in immune response were detected in an analysis by age group, with more than 93 percent of those in the 1.5μg and 3μg groups aged 3 to 5 years, 6 to 11 years, and 12 to 17 years producing antibodies against SARS-CoV-2 at day 28 after the second dose. In each age group, there were significant differences in GMTs between the 1.5 μg and 3.0 μg groups after the second dose, except in the group aged 12 to 17 years old in phase 1.

Based on their results, the authors recommend two 3μg doses of the vaccine for children and adolescents 3 to 17 years old.

The authors acknowledge some limitations to their study. T cell responses, which play an important role in SARS-CoV-2 infections, were not assessed in the study, though these have been investigated in related studies. The study involved a small number of participants, and all were of Han ethnicity, highlighting a need for larger studies in other regions and involving multi-ethnic populations. Long-term safety and immune response data were not available, though participants will be followed for at least 1 year. Owing to the small number of participants in the study, the results should be interpreted with caution as it was not possible to draw strong statistical conclusions, the researchers said.

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