Several years ago, Leonard Hayflick, PhD, was having dinner with friends in New Orleans when the subject of one of his discoveries came up. It had been decades since he developed the WI-38 human cell strain as a safer way to grow the viruses needed to produce vaccines against a number of diseases, and Hayflick was curious about the magnitude of its impact, according to one of his dinner companions that night, S. Jay Olshansky, PhD, professor of epidemiology and biostatistics at the University of Illinois at Chicago School of Public Health.
Olshansky remembered the conversation that took place over a meal during the annual meeting of The Gerontological Society of America.
“Len is known for having developed what’s called the ‘Hayflick limit’ for the limited number of cell replications, but very few people know much about WI-38 and the contribution it has made to public health,” Olshansky told Infectious Disease News. “We got to talking and he said, ‘I wonder how many lives have been saved as a result?’ I said, ‘You know, I think I can do this calculation for you.’”
Their conversation launched a study published this month by AIMS Public Health in which Olshansky and Hayflick, using decades-old prevalence rates, estimated that vaccines produced using WI-38 have prevented 4.5 billion cases of disease and 10.3 million deaths worldwide over the past 5-plus decades.
It took a while to come up with what Olshansky characterized as a conservative global estimate of WI-38’s impact. He and Hayflick collaborated on studies before, but this one took a number of years to finish.
“I was so busy doing other things, I didn’t get to it for a while,” Olshansky said. “When we saw the results, we were rather shocked by the number. I suppose we shouldn’t have been, but it was a very large number of people that have been influenced.”
Hayflick, a professor of anatomy at the University of California, San Francisco, developed the WI-38 human cell strain in 1962 at the Wistar Institute in Philadelphia. According to the study, WI-38 and its derivatives have been used in a “vast majority” of human virus vaccines since the 1960s.
At the same time that WI-38 was developed, the primary monkey kidney cells used to make polio vaccines were found to be contaminated with dangerous viruses common to monkeys, forcing an end to their production. According to the study, Hayflick’s discovery of WI-38 came at a fortuitous time, preventing a potentially deadly gap in coverage.
“Unlike monkey kidney primary cultures,” Olshansky and Hayflick wrote, “the importance of WI-38 is that (1) it is derived from a single donor, (2) it is free from contaminating viruses, and (3) it can be frozen for indefinite periods of time and tested for safety and efficacy before use in large-scale vaccine manufacture.”
WI-38 was distributed to human virus vaccine manufacturers for free and has been used to safely grow the viruses needed to make vaccines for polio, measles, mumps, rubella, varicella, herpes zoster, adenovirus, rabies and hepatitis A virus.
Olshansky and Hayflick researched U.S. prevalence rates for each disease in 1960 and assumed, for the purposes of the study, that those rates would have held steady through 2015 without the introduction of vaccines. For each disease, they calculated the impact between the first year that a vaccine using WI-38 became available for that disease and 2015.
According to their estimate, the number of cases of polio, measles, mumps, rubella, varicella, adenovirus, rabies and hepatitis A virus that has been averted or treated in the U.S. since vaccines made using WI-38 were introduced is 198 million. They estimated the total number of deaths averted from these diseases as approximately 450,000, including 633,000 fetal deaths from rubella.
For a conservative global perspective, Olshansky and Hayflick applied U.S. rates to the entire human population and came up with an estimate of 4.5 billion cases of disease that have been averted or treated worldwide since the introduction of vaccines developed using the WI-38 cell strain.
They calculated that 10.3 million lives have been saved globally, including 6.2 million in Asia and 1.6 million in Africa — numbers Olshansky considers to be underestimated.
“We’re assuming prevalence is the same everywhere else in the world as it is in the U.S. and we know that that’s highly unlikely,” he said. “Prevalence is likely to be higher elsewhere, but we wanted to provide sort of a floor. The number of people that [has]been influenced is likely to be significantly higher.” – by Gerard Gallagher
Olshansky SJ, et al. AIMS Public Health. 2017;doi:10.3934/publichealth.2017.2.127.
Disclosure: Hayflick and Olshansky report no relevant financial disclosures.