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Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
Vaccines prevent between 2.5 and 4 million deaths every year.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
According to the FDA, adverse drug events harmed or killed approximately 1,200,000 people in the United States in the year 2015.
Interferon was scarce and expensive until 1980, when the interferon gene was inserted into bacteria using recombinant DNA technology, allowing for mass cultivation and purification from bacterial cultures.