MEXICO CITY, Sept 24 (Reuters) - The COVID-19 vaccine by Pfizer-BioNTech (PFE.N) will be the only one used in Mexico for at-risk children aged 12-17, Mexico"s deputy health minister said on Friday. Mexico is expanding its vaccine campaign to children with health issues like cancer, diabetes or cardiovascular disease that make them vulnerable to the virus. "We can only use the Pfizer-BioNTech vaccine because it is the only one that has already been scientifically proven to be safe and effective in girls, boys and adolescents from 12 to 17 years old," Deputy Health Minister Hugo Lopez-Gatell said at a regular news conference. "It is not ruled out that other pharmaceutical companies in due course also present their analysis and demonstrate the vaccines can also be used in children and adolescents," he added. The government estimates it will give vaccines to between 750,000 and 1.5 million at-risk children initially. Mexico has applied so far for 97.5 million vaccine doses, according to government data. About 43.2 million people are fully vaccinated among its population of 126 million. Mexico has recorded 3,608,976 infections and 274,139 related deaths since the pandemic began. However health ministry officials have previously said that the real coronavirus numbers are likely significantly higher.