New oral polio vaccine found very effective in newborn infants: icddr,b study

A new study conducted by the scientists of the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) and partners has shown for the first time that a novel oral polio vaccine is effective for infants.

The study, recently published in The Lancet, found that the oral polio vaccine (nOPV2), developed for use in outbreak control, is safe and leads to the production of productive antibodies in a population of newborn infants who are not previously exposed to any polio vaccine, said a press release on Sunday.

The randomised, double-blind, controlled, phase 2 trial of the vaccine was conducted at icddr,b's Matlab Health Research Centre in Chandpur from 21 September 2020 to 16 August 2021.

The researchers identified women in their third trimester of pregnancy and invited them to enrol their infants in the study. 

It evaluated the safety, tolerability, and immunogenicity after one and two doses of nOPV2 administration at four weeks apart to the infants. The researchers also looked at some secondary outcomes.

The vaccine was found to be immunogenic, resulting in 99% of infants having protective neutralising antibodies.

Dr K Zaman, senior scientist in the Infectious Diseases Division at icddr,b who led the study, said, "The novel oral polio vaccine is safe and immunogenic in the age group that most needs to be vaccinated to stop the chain of polio transmission in at-risk communities."

"This information is particularly welcomed given that over 450 million doses have already been distributed under the WHO Emergency Use Listing procedure, with no age restrictions for recipients," he noted. 

"Our study supports the continued use of the vaccine. However, there is still no data on how nOPV2 may interfere with the Bivalent Oral Poliomyelitis Vaccine, the currently approved oral vaccine targeting types 1 and 3 polioviruses," Dr Zaman added. 

Overall, 327 infants received two doses of vaccine or placebo and among these 325 were tested for immunogenicity per protocol. The vaccine was safe and adverse event rates were similar in the vaccine and placebo groups.

Oral polio vaccines (OPVs) use live but weakened forms of the poliovirus to prime the immune system. On rare occasions, type 2 poliovirus used in traditional OPVs can mutate and reacquire neurovirulence — the ability to cause disease of the nervous system. 

Concerns about possible outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2), led the Global Polio Eradication Initiative to withdraw type 2 poliovirus from OPVs and target only types 1 and 3.

The World Health Organisation (WHO) recently authorised the use of a new OPV against type 2 poliovirus called nOPV2, which is less likely to revert to neurovirulence. 

However, the vaccine had only previously been tested on individuals who had received at least one dose of the inactivated polio vaccine (IPV), which is less effective than OPVs at preventing transmission of the virus. 

Thus, the findings of this new study will equip public health experts and policymakers with the evidence to inform the use of nOPV2 in newborns with no previous exposure to other polio vaccines, who constitute the most vulnerable group for polio transmission.