Referencia 42

Ortqvist A, Hedlund J, Burman LA, Elbel E, Hofer M, Leinonen M et al.
Randomised trial of 23-valent pneumococcal capsular polysaccharide vaccine in prevention of pneumonia in middle-aged and elderly people. Swedish Pneumococcal Vaccination Study Group.
Lancet 1998 Feb 7; 351 (9100): 399-403.
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