Everyone 6 months and older is recommended for annual flu vaccination with rare exception. For the 2016-2017 season, CDC recommends use of injectable flu vaccines–inactivated influenza vaccine (or IIV) or the recombinant influenza vaccine (RIV). The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) should not be used during 2016-2017. This page lists all people recommended to get a flu vaccine, who can and can’t get the flu shot and who should take precautions or talk to their doctor or other health care professional before vaccination. Talk to your doctor or nurse if you have any questions regarding which flu vaccine is best for you and your family.
Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies.  Recent research has shown that some common parasites , such as intestinal worms (., hookworms ), secrete chemicals into the gut wall (and, hence, the bloodstream) that suppress the immune system and prevent the body from attacking the parasite.  This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive.  In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants .  However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms.  Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies.  It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work.  For more information on this topic, see Helminthic therapy .