Many vaccines are made from the cells taken from a foetus during the 1960s.

If we count it takes for cells to reach the Hayflick limit multiplied by the number of cells in the human body, you end up with 120 years.

Second, it's hard to encounter cells that are grown in the laboratory - a fundamental step in the production of vaccines and drugs.

Scientists had gone around the division limit by continuously replenishing their cell supplies from new animals with fresh ones, or using cancer cells - since cancer does not play by the same rules as healthy tissue, and will continue to grow indefinitely.

Many vaccines are made by growing aggressive particles in cells, and then weakening or killing them to prevent disease from occurring.

The vaccine for polio had been made for decades in cells taken from the monkey kidneys, it was discovered later that some of them- were infected with a simian virus 40.

Although vaccines today are extensively filtered and contain no material from the cells in which they are grown, it is counted that in United States about 30 million people were infected between 1955 and 1963.

Those cells eventually turned into the "WI-38" cell line, which stands for foetus 38 of the Wistar Institute.

Over the years that followed, frozen cell vials were shared to hundreds of laboratories worldwide, and WI-38 is now the world's oldest and most available cell line.

Today the cells are used to make vaccines for: polio, mumps, rubella, varicella zoster, herpes zoster, rabies, hepatitis A adenovirus and measles.

And how can we justify its continued use?

WI-38 cells are mortal, but they can be grown for longer before they reach the Hayflick limit because the cells had divided relatively few times when collected.

Although there are a lot of cell lines in the U.S., WI-38 makes up most of the cells used, along with just another.

Finally, fetuses are thought to be the purest possible source of cells, as they are less likely to have catch up any viruses or bacteria from the outside world that could contaminate vaccines or confuse the experimental results.

Perhaps most striking in the development of the rubella vaccine is the linkage between the chilling origins of many cell lines and the benefits they provide.

Although it has been produced in WI-38 cells to this day, its early development depended heavily on cells taken from several different aborted fetuses - many of which had been aborted because their mother had been infected with the virus.

Read the original article "The controversial cells which saved 10 million deaths" at https://www.bbc.com/future/article/20201103-the-controversial-cells-that-saved-10-million-lives