Saliva samples are easy to obtain and useful for measuring antibodies to SARS-CoV-2 in children, which could facilitate epidemiological surveillance in school settings. The study, a collaboration between the Institute for Global Health in Barcelona (ISGlobal), an institution supported by the La Caixa Foundation, and the Sant Joan de Déu Hospital (HSJD), tracked more than 1,500 children who attended summer schools in Barcelona last year. The results are published in BMC Medicine.
One of the pressing issues during this pandemic is understanding children’s susceptibility to SARS-CoV-2 infection and their ability to infect others. An obstacle to answering this question is that most infections in children are mild or asymptomatic and are therefore missed. To determine if a person has been exposed to SARS-CoV-2 in the past, virus-specific antibodies should be looked for in the blood. Measuring the spread of antibodies over time in a group of children can provide very valuable epidemiological information. However, this requires techniques that are sensitive (able to detect low levels of antibodies) and minimally invasive (so they can be done often).
In this study, conducted through the Kids Corona platform, the team led by Carlotta Dobanio of ISGlobal and Yolanda Jordan of HSJD used saliva instead of blood to measure virus-specific antibodies in more than 1,500 children attending various summer schools in Barcelona. in 2020, as well as about 400 senior employees. Two samples of participant saliva, one at the beginning and one at the end of the camp stay, were analyzed and different types of antibodies (IgG, IgA and IgM) directed to different viral antigens were measured.
The results show that 3.2% of participants in the summer school developed antibodies between the first and second sample, which is indicative of new infections. This is 6 times higher than the infection rate calculated by weekly PCR screening. “It has been reported that some children may be antibody positive even though they are PCR negative, suggesting that they may generate an immune response that prevents the detection of SARS-CoV-2 infection,” explains Dobanjo, the first author of the study. It may also be due to the fact that asymptomatic children have a lower viral load or that they clear the virus faster.
In addition, the analysis showed that the percentage of new infections was higher in adults (2.94%) than in children (1.3%), which suggests differences in the dynamics of infection and transmission. Finally, contrary to what is observed in the blood, asymptomatic people have had higher levels of anti-spike antibodies in their saliva, suggesting that these antibodies play a protective role in the respiratory mucosa.
This means that antibodies against Spike in saliva can be used to measure the protective immunity of vaccination, especially in the case of intranasal vaccines. “
Gemma Moncunil, senior co-author of the study
“Earlier, we demonstrated in other Kids Corona studies that saliva is useful for detecting the virus by PCR. With this study, we demonstrate that this is also an effective and much more friendly way to measure antibodies, making it the ideal sample for children instead of a more invasive nasal swab, ”says Jordan.
“Saliva studies are much easier to perform and do not require specialized staff to collect them,” said Juan Jose Garcia, head of pediatrics at HSJD and coordinator of the Kids Corona study, which means that this strategy may prove to be very useful for measuring frequency in school settings and guiding decisions about the type of measures to be implemented.
Institute of Global Health in Barcelona (ISGlobal)
Added, K., et al. (2021) Degrees of conversion of antibodies to SARS-CoV-2 in saliva from children attending summer schools in Barcelona, Spain. BMC medicine. doi.org/10.1186/s12916-021-02184-1.