New York, Oct 1 : Children, between the ages of 12 and 18, who have received solid organ transplants appear to mount a more robust immune response than their adult counterparts after a standard two-dose vaccination regimen against SARS-CoV-2, the virus that causes Covid-19, according to a study. People who receive solid organ transplants (such as hearts, lungs and kidneys) often must take drugs to suppress their immune systems and prevent rejection. Such regimens may interfere with a transplant recipient's ability to make antibodies to foreign substances, including the protective ones produced in response to vaccines. "We found that nearly three-fourths of the paediatric transplant recipients we studied had a positive and protective antibody response after receiving two doses of the Pfizer/BioNTech messenger RNA (mRNA) vaccine, in contrast with many adult transplant recipients evaluated who needed a third dose," said Douglas Mogul, Associate Professor of Paediatrics at Johns Hopkins University School of Medicine. The study, published in the American Journal of Transplantation, looked at 57 paediatric solid organ transplant recipients who had received the Pfizer/BioNTech vaccine. The median age was 14 (ranging between 12 and 18 years old). Positive antibody levels against SARS-CoV-2 were seen in 73 per cent of the 45 children with available samples after two vaccine doses. In the 30 who had antibody titres measured after both their first and second shots, 17 per cent had negative titres after both, 33 per cent had a negative titre that became positive, and 47 per cent had positive titres throughout. One patient who had a positive titre after one dose that became negative after the second (3 per cent). The researchers report that no organ rejection or other unanticipated adverse events were seen among the study participants. Two patients tested positive for SARS-CoV-2 infection during the study. "Our preliminary findings suggest the possibility that the standard two-dose regimen for mRNA vaccines is safe in paediatric transplant recipients," said lead author Caroline Qin, a medical student at Johns Hopkins. "Further research is needed to show if two doses provide clinical protection and if not, the role that a third dose may play in boosting the immune systems of those unable to respond after two," Qin added. /IANS