Fig. 3: Evolution of neutralising antibody (NAB) half maximal inhibitory concentrations (IC50) between T4 (Nov/Dec 2021) and T5 (June/July 2022) among negative, infected, vaccinated children and adolescents, and those with hybrid immunity.

The evolution of neutralising antibodies (NAB) is shown by violin plots that display mirrored density for each NAB half maximal inhibitory concentration (IC50) (continuous distribution). Children and adolescents are categorised based on their exposure status (i.e., hybrid, vaccinated, infected, negative). Panel a 38 participants with hybrid immunity at T4 and T5. Panel b No children were observed in this panel, as it is highly unlikely to be hybrid in T4 and later only show evidence of vaccination at T5. Panel c No children were observed in this panel, as it is highly unlikely to be hybrid in T4 and later only show evidence of infection at T5. Panel d 60 participants vaccinated at T4 and with hybrid immunity at T5. Panel e 84 participants vaccinated at T4 and T5. Panel f No children were observed in this panel, as it is highly unlikely to be vaccinated in T4 and later only show evidence of infection at T5.  Panel g 33 participants infected at T4 and with hybrid immunity at T5. Panel h No children were observed in this panel. Panel i 143 participants infected at T4 and T5. Panel j 49 participants negative at T4 and with hybrid immunity at T5. Panel k 74 participants were negative at T4 and vaccinated at T5. Panel l 210 participants negative at T4 and infected at T5. Negative denotes seronegative at T4; Infected denotes seropositive and unvaccinated (T4 infected denotes seropositive based on anti-spike IgG prior to the T4 testing and unvaccinated, T5 infected denotes seropositive based on anti-spike IgG between T4 and T5 and unvaccinated); Vaccinated denotes vaccinated participants but negative in previous rounds and without evidence for anti-nucleocapsid IgG response. Children and adolescents with hybrid immunity were seropositive before getting vaccinated or were vaccinated and tested positive for anti-nucleocapsid-IgG antibodies. The dotted line indicates the NAB IC50 value threshold (50) for neutralising activity. Children and adolescents with NAB IC50 values above the threshold are assumed to have 50% or higher neutralisation capacity. Boxplots in panels show the median and interquartile range (IQR; whisker: 1.5 IQR). 60 children and adolescents are not shown in the figure (n = 31 participants were seronegative at T4 and T5, n = 29 participants had no data at T4). Source data are provided as a Source Data file.