ORAL POLIO VACCINE (OPV) – SOME CLARIFICATION. I’m a big OPV fan, but when I write about OPV I get negative feedback. So time to go through why I’m a fan and explain why I don’t see the same problems as some people do. Ready to get assumptions challenged? Follow this thread (1/n)
OPV was developed in the 1950s. At that time, polio was a problem. Epidemics followed epidemics, and though most people had asymptomatic disease, at its peak in the 1940s and 1950s, polio would paralyze or kill over 500,000 people worldwide every year (2/n)
After the introduction of the two polio vaccines, OPV and the inactivated polio vaccine (IPV), the incidence decreased. Cases due to wild poliovirus decreased by over 99% since 1988, from an estimated 350,000 cases then, to 33 reported cases in 2018 (3/n) who.int/en/news-room/f…
The only serious adverse events associated with OPV are rare cases of vaccine-associated paralytic poliomyelitis (VAPP) and the emergence of vaccine-derived polioviruses. VAPP is estimated at 2–4 cases/million birth cohort/year in countries using OPV (4/n) who.int/wer/2016/wer91…
Now to the two arguments I'm met with: 1) Nowadays, more polio cases are caused by vaccine than by wild virus. 2) A study from India showed that OPV cause non-polio acute flaccid paralysis (NPAFP). Hang in, I will explain why I’m still a fan (5/n)
It’s natural that once the wild virus is nearly extinct, the relative proportion of polio cases caused by vaccine will go up. In 2019, there were 59 cases of VAPP, but that is 0,0002% of the 350,000 cases that there were from wild polio virus in 1988 (6/n) apps.who.int/iris/bitstream…
Hence, if you want to have a world free of polio and polio paralysis, it is much better to have OPV than not to have OPV. Notably, if all children in the world were fully vaccinated with OPV, there would be no cases of VAPP. Now to the second argument (7/n)
India has used very frequent OPV campaigns to eradicate poliovirus. An ecological study linked the number of OPVs to the risk of getting NPAFP. As association was found: the number of OPV campaigns correlated with the number of NPAFP in the states (8/n) ncbi.nlm.nih.gov/pubmed/30111741
Internationally, the incidence of NPAFP is 1 to 2/100,000 in the under-15 population. In India, it was up to 25-35/100,000 in some states during the period with bimonthly OPV campaigns; it started declining again once the OPV campaigns became less frequent (9/n) 
As noted by the authors, correlation is not causation. There is no known biological mechanism to explain why OPP should cause NON-polio AFP. But even if somebody should feel concerned that there was an association, there are a couple of arguments more (10/n)
The association was only seen when India gave >6 OPV/year. No other country has given that many OPVs. In a typical child vaccination program, 4 doses are given. Campaigns in other places in the world are carried out 1-2 times/year (11/n)
Other countries not using OPV also see increases in NPAFP. E.g. in the US, there is now an “epidemic” of AFP and OPV has not been used since 2000. Thus, there can be other causes of AFP than OPV. This is why I’m not very concerned (12/n) mbio.asm.org/content/10/2/e…
Why am I a big fan of OPV, then? Not least because OPV seems to do more than just prevent polio infection. Already in the 1960-70s, Russian virologist Marina Voroshilova observed that OPV could protect non-specifically against influenza (13/n) ncbi.nlm.nih.gov/pubmed/2555836
In Guinea-Bissau, we observed that OPV given in campaigns was associated with 19% (5-32%) reduction in the risk of dying from any cause. Mortality was further 13% (4-21%) reduced with each additional dose (14/n) frontiersin.org/articles/10.33…
We conducted a randomized trial of OPV to newborns: those that received OPV with BCG had 32% (0-55%) lower risk of dying from any cause up until the time of OPV campaigns. The effect was pronounced if OPV was given within the first 2 days of life (15/n) academic.oup.com/cid/article-lo…
In a natural experiment, DTP was associated with 5 times higher mortality than no DTP – but it was 10 times higher mortality, if no OPV was given. Thus, OPV seemed to ameliorate the negative effects of DTP vaccine (16/n) linkinghub.elsevier.com/retrieve/pii/S…
In Denmark, OPV was associated with 15% (5-23%) lower risk of admissions for all cause infections. The effect was particularly pronounced for respiratory infections (27% (13-39%) (17/n) academic.oup.com/ofid/article/3…
Thus, in line with other live vaccines, OPV seems to have beneficial non-specific effects #NSEvac, reducing the risk of non-targeted infections. But now the plan is to stop OPV in 2024 and replace it with IPV. Is that a problem? Yes (18/n) sciencedirect.com/science/articl…
Non-live vaccines may have negative non-specific effects, particularly for females. IPV follows this pattern. We have found that IPV was associated with 52% (2-128%) higher female than male mortality (19/n) dx.doi.org/10.1097/01.inf…
Two randomized trials compared OPV and IPV back-to-back. A Finish trial found that those receiving OPV had less OM. sciencedirect.com/science/articl…. A Bangladesh trial found that those receiving OPV had less diarrhea of any cause. academic.oup.com/cid/article-lo… (20/n)
As calculated by others: “Replacement of OPV with IPV could translate to approximately 4000 deaths for each case of VAPP prevented, and might cause more than 300,000 additional deaths each year” (21/22) linkinghub.elsevier.com/retrieve/pii/S…
If you followed me this far: thanks for your patience, particularly if you are one of those, who have been concerned about OPV. I hope I have convinced you that OPV may not be that bad. I look very much forward to seeing if it works against COVID (22/22) eu.usatoday.com/story/opinion/…
