Young infants cannot receive flu vaccines for safety reasons, but they can inherit passive immunity from their mother if inactivated vaccines are administered to the mother during pregnancy. Influenza vaccination also helps to reduce the probability of reassortment.In general, influenza vaccines are only effective if there is an antigenic match between vaccine strains and circulating strains. Additionally, most commercially available flu vaccines are manufactured by propagation of influenza viruses in embryonated chicken eggs, taking 6–8 months. Flu seasons are different in the northern and southern hemisphere, so the WHO meets twice a year, one for each hemisphere, to discuss which strains should be included in flu vaccines based on observation from HA inhibition assays. Other manufacturing methods include an MDCK cell culture-based inactivated vaccine and a recombinant subunit vaccine manufactured from baculovirus overexpression in insect cells. Antiviral chemoprophylaxis
Influenza can be prevented or reduced in severity by post-exposure prophylaxis with the antiviral drugs oseltamivir, which can be taken orally by those at least three months old, and zanamivir, which can be inhaled by those above seven years of age. Chemoprophylaxis is most useful for individuals at high-risk of developing complications and those who cannot receive the flu vaccine due to contraindications or lack of effectiveness. Post-exposure chemoprophylaxis is only recommended if oseltamivir is taken within 48 hours of contact with a confirmed or suspected influenza case and zanamivir within 36 hours.
Macrocytosis is the enlargement of red blood cells with near-constant hemoglobin concentration, and is defined by a mean corpuscular volume (MCV) of greater than 100 femtolitres (the precise criterion varies between laboratories). The enlarged erythrocytes are called macrocytes or megalocytes (both words have roots meaning "big cell"). As a symptom its cause may be relatively benign and need no treatment or it may indicate a serious underlying illness. Causes
In humans, most commonly (especially when the increase in size is mild, and just above normal range) the cause is bone marrow dysplasia secondary to alcohol use disorder. Poor absorption of vitamin B12 in the digestive tract can also cause macrocytosis. Gastrointestinal diseases that may cause macrocytosis include celiac disease (severe sensitivity to gluten from wheat and other grains that causes intestinal damage) and Crohns disease (inflammatory bowel disease that can affect any part of the gastrointestinal tract). Other causes may include:

megaloblastosis (vitamin B12 or folate deficiency) because slowly dividing erythrocytes accumulate cytoplasmic components, resulting in larger-than-normal cells. hypothyroidism
chronic obstructive pulmonary disease (COPD)
aplastic anemia
reticulocytosis (commonly from hemolysis or a recent history of blood loss). liver disease because of an increase in circulating phospholipids and cholesterol, which bind on erythrocytes and induce membrane expansion
myeloproliferative disease
myelodysplastic syndrome which most commonly presents with macrocytic anemia
chronic exposure to benzene
pregnancy (most common, and requires no treatment as the person affected will return to normal post-partum)
Certain anti-inflammatory drugs, e.g. salazopyrin, azathioprine. Complications
No complications arise from macrocytosis itself and a prognosis will be determined from its cause. See also
Macrocytic anemia

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