Mortality and survival in nonagenarians during the COVID-19 pandemic: Unstable equilibrium of aging oleh Daria A. Kashtanova, Veronika V. Erema, Maria S. Gusakova, Ekaterina R. Sutulova, Anna Yu. Yakovchik, Mikhail V. Ivanov, Anastasiia N. Taraskina, Mikhail V. Terekhov, Lorena R. Matkava, Antonina M. Rumyantseva, Vladimir S. Yudin, Anna A. Akopyan, Irina D. Strazhesko, Irina S. Kordiukova, Alexandra I. Akinshina, Valentin V. Makarov, Olga N. Tkacheva, Sergey A. Kraevoy, Sergey M. Yudin