A 10-month-old baby in Beed district, Maharashtra who was recently diagnosed of polio caused by the vaccine-derived poliovirus (VDPV) type 2 turns the spotlight on the shortcomings of using a live, weakened polio virus in oral polio vaccine.
Dr. T. Jacob John , member of the WHO committee on global polio eradication, in an email toR. Prasad , makes a strong case for quickly introducing injectable polio vaccines, along with oral vaccine, for better protection and prevention of VDPV cases.
What do you think caused the vaccine-derived polio virus (VDPV) type 2 in the baby?
Obviously the baby was undervaccinated and unprotected from polio. Also, obviously the child was infected by a vaccine-derived poliovirus from another person. Therefore, it was the combination of deficient number of doses plus the unlucky event of getting infected with a vaccine-derived virus. Not every child who gets infected with VDPV will become paralysed — so twice unlucky.
Does the emergence of VDPV reflect the lack of polio coverage in a particular area?
Yes. If coverage is good, VDPV cannot emerge or cause polio even if it is circulating silently. The two risk factors for emergence of VDPV are lower than adequate coverage and the continued use of OPV.
Is the VDPV equally capable of causing disease as the wild polio virus?
[There is] no accurate measure. VDPV may cause polio less frequently than the wild poliovirus; no one knows the ratio exactly. The point is, one case of VDPV means a large outbreak of infections already. Such outbreaks are very quickly put down with just two or three OPV campaigns.
Why do we see more of type 2 VDPV cases?
During the last 12 years — 2000 to 2011 (we have a count of only “circulating” VDPVs, not all VDPVs) globally there were 478 cases of type 2, 79 of type 1 and nine of type 3.
Of all circulating VDPV cases, 85-90 per cent was due to type 2; Type 1 was less often and type 3 was least often. These are biological phenomena as observed. Among the three viruses in OPV, type 2 is the most transmissible; hence the higher frequency seems to be due to this property of type 2 vaccine virus.
Why did the WHO recommend OPV in the first place?
[OPV was] believed to be highly efficacious (as live virus), safe (due to attenuation) and offer high degree of mucosal immunity and herd effect (slowing down of wild polio virus circulation). [The efficacy, herd effect and safety are] very relative, with wide geographic variations. [But it is] inexpensive and easy to give as oral drops.
Were cost and easy administration the only reasons for WHO recommending OPV?
There were experts who believed OPV was superior, without actual evidence of its superiority or inactivated polio vaccine’s (IPV) inferiority. [Unlike IPV that is injected], that belief was because OPV is given by mouth and vaccine viruses infect gut mucosa. We know from many other vaccines that mucosally infectious vaccines are not necessary to protect against diseases caused by mucosally infectious pathogens; there is no reason to suspect that IPV is any different. I do not believe OPV is superior to IPV.
What prompted India to adopt OPV and continue with it (despite its problems) even as developed countries switched to IPV years ago?
Decision making was mainly by administrators and not by public health experts or technocrats. And administrators may not be reading scientific literature. WHO recommended OPV in the Expanded Programme of Immunisation (EPI) and India complied without internal consultations or using Indian scientific information which spoke against OPV in favour of IPV. Our main problem was very low effectiveness of OPV, which was the reason why India had inordinate delay in eradicating wild polioviruses. We had to develop Type 1 and Type 3 “monovalent” OPV with higher efficacy to achieve success in 2011.
WHO was not convinced (until after failing to eliminate polio in India by 2005) that India (and other similar countries) had a problem with OPV — and our government had ignored Indian problems of very low effectiveness of OPV that was very well documented right from 1972.
Despite knowing that tropical conditions and denser population weakens the OPV immunity, why is India still continuing with OPV?
We were fighting a war against polio without a ‘war General’ — there was no official identified as the person in charge of, and accountable for, polio eradication. So, India followed WHO blindly, without independent assessment through Department of Health Research or through any agency.
Even six months after WHO’s recommendation to phase out type 2 from OPV and introduce IPV and use it along with OPV, what prevents the government from making a switch?
It will take time for a government to make a policy change and necessary program redirection. But things are moving now. However, there is another problem — high coverage with IPV requires a well performing EPI. Unfortunately, DPT coverage nationally for the third dose is stuck at 62 per cent. For IPV to be adequate we need at least 85 per cent coverage.
A WHO vaccinologist had gone on record stating that injectable vaccine is 10 times costlier than OPV. Your comments.
IPV is more expensive to produce, but the prices at which vaccines are sold are not the same as cost of production. OPV is purchased by the billions of doses and therefore it has to be much cheaper than IPV which was purchased only by rich countries and therefore companies did not have volume effect or competition to bring prices down. There were only two major IPV manufacturers. OPV has many more manufacturers.
Since the OPV programme costs about Rs.1,000 crores, will the cost of IPV not match that of OPV?
IPV has been promised at about $1 a dose by Serum Institute of India, if bulk ordered. In that case the price advantage is reversed!
How many injectable vaccine doses are needed and at what time periods to protect a child?
If first dose is given beyond the window of high maternal antibody, namely beyond eight weeks of age, and if second dose is given after an interval of eight weeks or more, just two doses will protect 100 per cent of children. Many countries follow a three-dose schedule. So perhaps a third dose could be planned — but no more are needed for very long-term protection.
For how long should OPV be given along with injectable vaccines before OPV is discontinued?
That needs careful assessment; no quick answer. But I can tell you that the main purpose of introducing IPV is for safely discontinuing OPV altogether.
But why should IPV be given along with OPV before the OPV programme is discontinued? Did every country that made a switch follow this protocol?
If OPV is withdrawn VDPV cases will increase. To pre-empt that we need to create an umbrella of immunity using IPV.
No, not all countries had to overlap both vaccines. Countries with very high (90 per cent or more) coverage simply switched over from OPV to IPV. Some countries use both vaccines in sequential schedule, as an interim tactic. Within this decade all countries will have to discontinue OPV.
Considering that fewer injectable vaccines are required, will the compliance not be superior to 15 OPV doses per year?
Not necessarily; OPV is being given in campaigns when we can get very high coverage. Where EPI is weak, campaigns can be very effective with high coverage like in India. So we have to ensure that EPI achieves high coverage in all States.
