Red blood cells, erythrocytes, under a microscope. Image by Drs. Noguchi, Rogers and Schechter via Wikimedia Commons
Another one of the Canadian/Netflix on demand series, Between season 2 became available in June. A virus kills all inhabitants aged over 21 in a US town called Pretty Lake. The town is quarantined and the children and young adults are left to fend for themselves, leading to a YA “Lord of the Flies”. Of course, there’s a government conspiracy, which creates an unlikely situation of supply airdrops absence. But despite a few plot holes, The characters are compelling, the plot moves along nicely.
Unfortunately, unlike in my favorite human cloning series, Orphan Black, the science of Between is completely bogus. A scientist who sneaked into Pretty Lake with an experimental vaccine looks at something round and red swirling on the screen (red blood cells?) and the vaccine represented by a yellow shimmering circle around them. He says that the virus sits inside cells and eats them from inside out, which is represented by churning and undulating cells as if an alien is trying to get out. The cells resist the virus until the 21st birthday date when boom! cells collapse and the person dies.
21 is the age of adulthood in the US when you suddenly allowed to drink, while you could marry, drive a car and join the Army before that magical date. From the biology point of view, 21th birthday is a completely arbitrary date. A virus wouldn’t know when precisely you were born – it’s virus, not a notary. In the absence of a document, it’s difficult to even estimate a persosn’s age – people who don’t have their birth certificate pass as underage for years and a convincing fake ID would age you.
Yes, there are viruses, which cause diseases in (mostly) children, for example, notorious mumps, measles, and rubella viruses. This apparent age specificity is caused by children’s underdeveloped immune systems as it’s still possible to get infected as an adult if you miss the childhood infection or not vaccinated. Assuming, that it’s possible to create a virus, which targets adults, it should hit anybody who reached an age of puberty, which can vary between 10 and 20 depending on the environmental conditions.
It’s the general condition of your body that would matter to a virus, not your birthdate. We all heard about a sprightly 90 yeas old, who run marathons and know 30 y.o. who look and have the health conditions of people of twice their age.