This year's influenza pandemic has been like nothing I have ever seen in 13 years of medical practice. I'd like to talk quickly about what is circulating, what the vaccine covers, and what the efficacy findings are so far.
There are two major strains of influenza circulating in the northern hemisphere. The first is an Influenza A H3N2 variety. While this virus is well-matched to the vaccine (with 98.5% of viruses inhibited by ferret antisera raised by the vaccine), the production of the virus on eggs seems to lead to some genetic alterations in the surface antigens that reduce the protection offered by the immunization. This is true just about any year an H3N2 Infuenza A is predominant. So far, in the USA, the immunization seems to be ~33% effective at preventing disease and ~50% effective at preventing death. Now, I will point out that 33% is also 33% higher than the zero percent you get if you don't take the shot.
The other strain is an Influenza B Victoria Lineage. According to the CDC, so far influenza B virii have been responsible for ~15-20% of disease burden. That said, in my community I have been keeping track and I have seen about 1/3 of the disease burden come from Flu B, although my rapid tests that I have don't distinguish the different lineages. We usually see influenza B later in the season, in February and March, but this year I got my first case in November and I have been seeing a high disease burden all through the season. The good news is that the immunization usually does a better job against influenza B, with an efficacy of ~60-70%, and it is well-matched to the two circulating strains this year.
The immunization is made by propagating virus on chicken eggs and then breaking the virus particles apart with formaldehyde. The formaldehyde is then washed out, an adjuvant and some stabilizing agents are added, and the vaccine is packaged. Because the USA does not use any "live virus" vaccines, the immunization cannot make you sick, although the immune activation from the vaccine can make you feel a bit off for a day or two.
As for oseltamivir ("TAMIFLU") this is an inhibitor of an enzyme on the surface of the virus particle called neuraminidase. Human cells are covered by a layer of gooey polysaccharide, and this makes it difficult for virus particles to exit the cell. Neuraminidase allows the virus particles to break down this gooey layer and float off on their merry way. Inhibiting neuraminidase prevents virii from leaving infected cells and reaching the cell membrane of uninfected cells. The trouble is that by the time you get oseltamivir on board, the benefit is modest. It only shortens the duration of the disease by a mean of 12 hours (optimistically) and there is only the sketichest evidence that it decreases hospital admission rates or severe complication rates. Side-effects are usually mild and include GI upset and a metallic taste in the mouth. If you have been sick for more than 48 hours, oseltamivir is of no benefit at all.
My experience is that in healthy children and young adults, this is a 3-5 day disease.
For those of you who are interested in some technical details, here is the CDC seasonal influenza page, called "FluView."https://www.cdc.gov/flu/weekly/