WFH as % of median reference value is calculated this way:
  
    
      
        
          W
          F
          H
        
        =
        
          
            
              weight of a given child
            
            
              median weight for a given child of that height
            
          
        
        ×
        100
      
    
    {\displaystyle \mathrm {WFH} ={\frac {\mbox{weight of a given child}}{\mbox{median weight for a given child of that height}}}\times 100}
  Cutoff points may vary, but <80% (close to −2 Z-score) is often used.
Research advancements in the field
While it has been commonly known that the influenza virus increases ones chances of contracting pneumonia or meningitis caused by the streptococcus pneumonaie bacteria, new medical research in mice indicates that the flu is actually a necessary component for the transmission of the disease. Researcher Dimitri Diavatopoulo from the Radboud University Nijmegen Medical Centre in the Netherlands describes his observations in mice, stating that in these animals, the spread of the bacteria only occurs between animals already infected with the influenza virus, not between those without it. He says that these findings have only been inclusive in mice, however, he believes that the same could be true for humans. Mechanism of disease manifestation
Three stages can be used to categorize the infection process of pneumococcal pneumonia: transmission, colonization, and invasion. The Streptococcus pneumoniae (S. pneumoniae) leave the colonized host via shedding in order to be transmissible to new hosts, and must survive in the environment until infection of a new host (unless direct transmission occurs). Animal models have allowed scientists to have an increased understanding of these stages of infection. Transmission
In order for transmission to occur, there must be close contact with a carrier or amongst carriers. The likelihood of this increases during colder, dryer months of the year. The probability of transmission is shown to proliferate in coordination with other upper respiratory tract (URT) infections. Animal models have allowed for an increased understanding of the transmission stage during infection.