Oral Polio Vaccines (OPV)

Oral poliovirus vaccines (OPV) have been the mainstay in the fight against polio. There are different types of oral poliovirus vaccine, which may contain one (mOPV), a combination of two (bOPV), or all the three (tOPV) serotypes of attenuated poliovirus.

Monovalent oral polio vaccines (mOPV):
These contain only one of the three serotypes of OPV. They are more effective than tOPV in conferring immunity against the targeted serotype, but do not provide protection to the other two types. Monovalent OPVs for type 1 (mOPV1) and type 3 (mOPV3) poliovirus were licensed in 2005

Trivalent oral poliovirus vaccine (tOPV)
Prior to April 2016, tOPV was the predominant vaccine used for routine immunization against poliovirus. Also called the ‘Sabin vaccine’, tOPV consists of live, attenuated polioviruses of all three serotypes.
The trivalent vaccine was withdrawn globally in April 2016

Bivalent oral poliovirus vaccine (bOPV)
Following April 2016, the tOPV was replaced with the bivalent OPV (bOPV) in routine immunization around the world. This is because continued use of tOPV would be a continuous source of type 2 circulating vaccine-derived polioviruses (cVDPV2), despite the wild type 2 virus being eradicated in 1999
Bivalent OPV contains only serotypes 1 and 3.

Identification features of bOPV
The vaccine is available in small glass bottles or plastic tubes having a vaccine vial monitor (VVM) on it. The lid has to be opened and replaced with a plastic dropper.
The dropper supplied with bOPV is white, narrower and smaller as compared to the one supplied with rotavirus vaccine.
(Note: VVM is now being used on other vaccines as well, e.g., IPV, Pentavalent vaccine, measles and hepatitis B)

Type of vaccine
Live attenuated

Route of administration
Oral

Dose
Two drops

Whether part of NIS?
Yes

Schedule
As under NIS
• “Zero” dose at birth
• First, second, and third doses at 6th, 10th, and 14th weeks of age, respectively, for primary immunization (these are given along with the routine doses of Pentavalent and rotavirus vaccines)
• Booster dose at 16-24 months (this is given along with DPT booster, Measles-2 and vitamin A dose)
Pulse polio immunization (PPI):
To be given as and when planned by the local authorities.
Between 2005 and 2016, monovalent OPV has been used for PPIs. P1 strain mOPV was used in some districts and mOPV (P3) in other areas.
Since 25th April 2016, only bOPV (having polio virus type 1 and 3) has been in use for routine immunization as well as for pulse polio campaigns.

Diluent
None

Constituents
Contains live, attenuated virus type 1 and 3 as given below:
 10 6.0 CCID50 of Type 1 Poliomyelitis virus
 10 5.8 CCID50 of Type 3 Poliomyelitis virus7

Side effects
Very rarely, Vaccine-associated paralytic polio, seen more with type 3.

Contraindication
Immunocompromised state in self or a household as this is a live vaccine.
Immunocompromised states include HIV positive, malignancy, etc.
IPV is an alternative to bOPV for protecting the immunocompromised individuals.

Storage
Long term storage is recommended at -20°C, i.e., in a deep freezer.
Once thawed, the liquid vaccine should be stored between 2-8˚C
During an immunization session OPV should be kept in ice or on the ice pack.

Describe the method of administering OPV drops.
• The child's neck is tilted back gently.
• The cheeks are gently squeezed (or else, the nose can be pinched) to make the child open her mouth.
• Two drops are allowed to fall off from the dropper onto the tongue of the child.
• If the child spits the vaccine out, repeat the process.

What are the instructions given to mother after OPV drops?
The mother is instructed to withhold hot fluids for half an hour after the drops. She may breastfeed as and when the child demands.

What happens if more than two drops are given?
Usually there is no problem. Occasionally if too large a dose is given, the child may have mild diarrhea. We give two drops only as this is sufficient and any higher dosage is not needed.

Is there a killed type of polio vaccine?
Another type of polio vaccine is the killed polio vaccine. It is called as Salk vaccine. This is also known as inactivated polio vaccine (IPV). This needs to be injected and has the antigens of all the three types of polio virus.

Advantages of OPV over IPV
• It is easy to administer orally and does not require training in injections or special equipment.
• Both humoral (antibodies) and intestinal immunity (local gut immunity) are induced.
• Small dose is required as agent multiplies in the host and hence it is economical.
• Vaccine virus may be transmitted to the unimmunized contacts too, thereby spreading the immunity to them also.

Disadvantages of OPV as compared to IPV (Salk vaccine).
• Live Sabin polio vaccine has lesser efficacy than the killed Salk vaccine.
• Requires strict maintenance of cold chain right till the point of vaccination.
• Live Sabin vaccine is contraindicated in the immunocompromised and during pregnancy.
• There is very small risk of the vaccine virus regaining virulence and causing paralytic polio. This is known as vaccine-associated paralytic polio (VAPP). The risk is one case per 4 million doses. There is no such risk with IPV.

Protective efficacy and duration of bOPV.
Protective efficacy 70-80% and duration is lifelong.

Should a child having diarrhea or other sickness be given OPV drops?
OPV drops can also be given to children who have diarrhea or other illnesses, as it usually does not react to other drugs or antibiotics.

What is pulse polio immunization (PPI)?
This is simultaneous administration of bOPV to all the under-5 children of the area. PPIs are organized in two rounds, 4–6 weeks apart. These doses of bOPV are over and above the routine immunization with bOPV and are not to be counted. All the children including those born on the same day as the PPI day should receive the dose.

The strategies for polio eradication in brief.
• Pulse polio rounds
• High coverage with routine immunization
• Efficient acute flaccid paralysis surveillance
• Prompt and efficient outbreak control for a confirmed or suspected polio case

What is the zero dose of bOPV?
Zero dose of bOPV is given to the newborn immediately after birth if the opportunity exists. This dose is not to be counted as a part of routine immunization with OPV which begins at 6 weeks. Hence this dose is called as “zero dose” The purpose of this dose is to give at least one dose of OPV in case the child does not get a chance to get immunized.
Mostly this is possible in institutional births when BCG and hepatitis B (birth dose) is also given along with the zero dose of bOPV.

Why type-2 strain has been removed from OPV for both routine and supplementary immunization activities (SIAs)?
With the transmission of Wild type-2 virus already interrupted, the only cases of type-2 paralytic polio were being caused by the type 2 serotype component in trivalent OPV. Over 90% of cVDPV cases were due to the type 2 component. Hence the decision to remove type 2 strain from all OPV has been taken.

Which step has been taken to ensure that immunity against type 2 poliovirus does not wane in the population after switching to bOPV?
The switch to bOPV was preceded by the introduction of a single dose of IPV along with the third dose of OPV in October 2015 in select states. IPV contains all the three poliovirus antigens.
The schedule for IPV was later modified to two fractional intradermal doses at 6th and 14th weeks to optimize the usage of IPV

Isn’t there a risk for VAPP by type-1 and type-3 strains too?
Yes, there is a small risk of VAPP and vaccine-derived polioviruses (VDPV), with the two remaining strains too. Yet the success of the Global Polio Eradication Initiative has recognised the value of OPV.
Once wild poliovirus transmission has been interrupted, the only cases of poliomyelitis will be caused by OPV and Poliovirus will be finally eradicated only when OPV use is discontinued.
Hence in the final phases of eradication, it is planned to phase out OPV and replace it completely by IPV.

References:

1. GOI. Immunization Handbook for Medical Officers. New Delhi: Department of Health and Family Welfare; 2016.
2. Park K. Epidemiology of communicable diseases. In: Park's Textbook of Preventive and Social Medicine, 24th ed. Jabalpur, India: M/S BanarasidasBhanot Publishers; 2017.
3. IPV Training Modules and Communication Documents, Pan American Health Organization (PAHO) website. Available at: http://www.paho.org/hq/index.php?option=com_content&view=article&id=1046... , accessed on 18th October 2017
4. GOI 2015. Introduction of Rotavirus Vaccine in the UIP, OPERATIONAL GUIDELINES. Immunization Division, Ministry of Health & Family Welfare, New Delhi
5. Park K. Epidemiology of communicable diseases. In: Park's Textbook of Preventive and Social Medicine, 20th ed. Jabalpur, India: M/S BanarasidasBhanot Publishers; 2009.
6. GOI 2017. Ministry of Health and Family Welfare. Available at: http://mohfw.nic.in/sites/default/files/186048546481489664481.pdf accessed on 26th October 2017
7. Summary of product characteristics. Bivalent poliomyelitis vaccine, Panacea Biotech. Available at: http://www.cdsco.nic.in/SMPC/Panacea%20SmPc%20(Sanofi%20Pasteur).pdf Accessed on 26th October 2017

National Immunization Schedule in India; 2017: http://www.ihatepsm.com/blog/national-immunization-schedule-india-2017

Rotavirus vaccine: http://www.ihatepsm.com/blog/rotavirus-vaccine

Pentavalent vaccine: http://www.ihatepsm.com/blog/pentavalent-vaccine

BACILLE CALMETTE GUERIN (BCG) VACCINE: http://www.ihatepsm.com/blog/bacille-calmette-guerin-bcg-vaccine

IPV (INACTIVATED POLIOVIRUS VACCINE): http://www.ihatepsm.com/blog/ipv-inactivated-poliovirus-vaccine

DT & TT Vaccines: http://www.ihatepsm.com/blog/dpt-and-tt-vaccines

Oral Polio Vaccines (OPV): http://www.ihatepsm.com/blog/oral-polio-vaccines-opv

Measles Containing Vaccines (MCV): http://www.ihatepsm.com/blog/measles-containing-vaccines-mcv

HEPATITIS B VACCINE: http://www.ihatepsm.com/blog/hepatitis-b-vaccine

JAPANESE ENCEPHALITIS (JE) VACCINE: http://www.ihatepsm.com/blog/japanese-encephalitis-je-vaccine

Pneumococcal Conjugate Vaccine (PCV): http://www.ihatepsm.com/blog/pneumococcal-conjugate-vaccine-pcv

RABIES VACCINE: http://www.ihatepsm.com/blog/rabies-vaccine