The case for vaccination of children under 12 years of age against COVID-19

In a recent study published on the prepress server medRxiv *, the researchers assessed the need for vaccination against coronavirus disease 2019 (COVID-19) in children aged 12 years or younger. To this end, the researchers compared the clinical characteristics observed in unvaccinated children during the delta jump (B.1.617.2) in China with those of the vaccinated group over 12 years of age.

This analysis found that young children may be critical latent spreaders of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, the causative agent of COVID-19). Thus, the present study shows that young children 12 years of age and younger urgently need vaccination to mitigate the spread of SARS-CoV-2 caused by this particular population.

study: Need for vaccination against COVID19 in children <12 years of age: Comparative evidence of clinical characteristics in patients during a recent Delta jump (B.1.617.2). Image credit: smile23 /


The ongoing COVID-19 pandemic has caused more than 250 million infections and more than 5.1 million deaths worldwide. Several new SARS-CoV-2 mutants include Alpha, Beta, Gamma, Lambda and Delta.

The Delta variant, first identified in Maharashtra, India in late 2020, has spread rapidly around the world. In Guangzhou, China, the Delta variant was first announced on May 21, 2021.

COVID-19 vaccines are effective against the Delta variant. To this end, these vaccines appear to provide protection and reduce the severity of symptoms and hospitalization rates in individuals vaccinated against COVID-19. Despite these observations, neutralizing antibodies produced by vaccination or previous SARS-CoV-2 infection were less effective against the SARS-CoV-2 Delta variant than their effectiveness against other variants of SARS-CoV-2.

Importantly, according to the US Centers for Disease Control and Prevention (CDC), people who have not been vaccinated are 11 times more likely to become infected with COVID-19, which shows the important role of vaccines and the protection they render from Delta option. The lack of worldwide mass vaccination of children and adolescents under the age of 12 could cause this population to host the Delta variant, as well as additional mutant strains of SARS-CoV-2 that could further exacerbate the epidemic.

With the weak vaccine elicited by neutralizing antibodies against the SARS-CoV-2 Delta variant, there is an impending fear of severe breakthrough infections.

Survey results

The study group included a total of 226 individuals with positive SARS-CoV-2 Delta VOC, which was confirmed by SARS-CoV-2 polymerase chain reaction (PCR). All study participants were admitted to Putian University Liaison Hospital.

The researchers divided these individuals into two groups, including those 12 years of age and younger who had not been vaccinated. This group consists of 77 middle-aged people 9.

The second group includes those over 12 years of age, most of whom have been vaccinated with a Chinese inactivated virus vaccine from Sinopharm or Sinovac. This group consists of 149 people with an average age of 39 years.

The researchers measured the SARS-CoV-2 real-time PCR threshold (CT) values ​​and serological results, which included a blood test, biochemical analysis, C-reactive protein (CRP), interleukin-6 (IL-6), SARS -CoV-2 IgG antibody titer, coagulation function and microbial testing. They also obtained data on clinical manifestations and compared observations.

Children show mild symptoms, activated innate immunity, highlighted by higher lymphocyte counts, lower overall inflammatory reactions and a good prognosis. However, the CT value of the nucleic acid of the vaccinated group increased to a greater extent compared to unvaccinated individuals, indicating a faster clearance of the virus due to vaccination.

The researchers also evaluated the nucleic acid negative (NAN), which is defined as “the duration from the first day of a positive nucleic acid report to the time of the second negative nasopharyngeal swab test of two consecutive negative nucleic acid tests.” To this end, vaccinated patients over 12 years of age had lower antibodies to COVID-19 on immunoglobulin M (IgM) and IgG, but a longer NAN time than those who had not been vaccinated at 18 days, respectively. 16 days. The time for NAN is closely related to the elimination of the virus and its infectivity.

Points represent IgM / IgG levels in children <12 years of age (group 1) and those ≥ 12 years of age (group 2). The pictures show the median and interquartile range (IQR), and the mustache represents the maximum and minimum values. The results show lower levels of IgM and IgG of COVID antibodies on admission and IgG levels on convalescence. [0.13(0.00,0.09) vs. 0.12(0.03,0.41), p<0.05; 0.02(0.00,0.14) vs. 1.94(0.54,6.40), p <0.05; 5.46(2.41,9.26) vs. 73.63(54.63,86.55), p< 0.05, respectively], but higher levels of IgM antibodies in convalescence [1.05(0.51,2.31) vs. 0.51(0.20,1.69), p=0.016].

Therefore, based on these observations, the researchers hypothesized that there was a slow clearance of the virus in the unvaccinated younger group. This observation suggests that if children 12 years of age and younger remain vaccinated, they may carry the virus longer and become sources of viral transmission.


The present study reported increased NAN time in young children and, in contrast, increased nucleic acid CT and rapid and higher antibodies to COVID-19 in the vaccinated population over 12 years of age. Based on these results, the researchers suggest that unvaccinated children are critical hidden vectors of the virus; thus, vaccination against COVID-19 in children should be promoted in an orderly manner, with close monitoring for efficacy and any adverse reactions.

While the Chinese government recently approved the emergency use of the COVID-19 vaccine for children aged 3-17 years, this study critically compares the clinical features that support the need for vaccination among children.

Researchers have called for further studies to determine the underlying mechanisms of immune function in children under 12 years of age.

*Important message

medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered convincing, guiding clinical practice / health-related behavior, or treated as established information.

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