Flu Immune 500

From just a few days to several weeks, many estimates are often provided for the length of the “contagious period” for the flu. While these estimates are all correct, they are only correct in certain circumstances. A good look at the underlying mechanism of influenza infection can lead to a better understanding of how long people are infectious when carrying the virus.

The influenza virus functions much like other viruses, with similar replication patterns and incubation periods. The host organism catches the virus through some means of transmission, usually bodily fluids such as saliva or mucus. After initial infection, the virus “incubates” by attacking individual cells and commandeering their replication systems to build more virus particles. When the cells have swelled with newly synthesized virus particles, they burst and the viral agents spread to adjacent cells and tissues.

Simple intuition would suggest that while the virus is incubating, it is unlikely that the virus can be easily spread. This is a solid assumption that generally holds true. Upon immediate infection, the human host cannot transmit the virus, but their infectiousness increases quickly the longer the virus incubates.

Once the virus has spread throughout the body and the symptoms of influenza have appeared, the host is more contagious than ever. This makes perfect sense for two reasons. First, the virus particles are most plentiful at this point. As the body builds immunity, the particles are destroyed and the human becomes healthy again. This means that a person’s contagious period begins to decline, though it doesn’t immediately disappear, as soon as the immune system mounts its response. Secondly, the symptoms that accompany full infection help the disease spread. Runny nose, coughing and sneezing all spread virus particles and contaminate other surfaces. Its common sense that while the symptoms are in full swing the flu is most contagious.

The length of the contagious period, based on the prior reasoning, depends on how long the body’s immune system takes to respond and how long the symptoms last. For healthy individuals, the symptoms last 5-7 days after they appear. In immunocompromised individuals, the very young, and the elderly, the virus can persist for up to two weeks.

Combining the minor contagious period immediately following infection and the time the virus spends in the system, most healthy individuals are contagious for about 8 days after the initial infection. This is about one day before symptoms appear and another week following.