1 National Institute for Infectious Diseases (INMI), Lazzaro Spallanzani IRCCS, Via Portuense 292, 00149 Rome, Italy. Electronic address: emanuele.nicastri@inmi.it.
2 National Institute for Infectious Diseases (INMI), Lazzaro Spallanzani IRCCS, Via Portuense 292, 00149 Rome, Italy.