A new bivalent polio vaccine is as effective in immunizing infants as are existing monovalent vaccines and more effective than a widely used trivalent vaccine, researchers with the World Health Organization have found.
In an article published online Oct. 26 in the Lancet, Dr. Roland W. Sutter of WHO in Geneva, and his colleagues, presented findings on a randomized, double-blind controlled trial of a two-dose oral vaccine containing antigens to wild poliovirus types 1 and 3 that was conducted in India and enrolled 900 infants. The researchers randomized the infants into five groups and examined the immunogenicity of three existing monovalent vaccines, the bivalent 1 and 3 vaccine, and a trivalent vaccine containing antigens to types 1, 2, and 3.
Recent polio eradication efforts have favored the use of monovalent vaccines, because trivalent vaccines – while offering the convenience of delivering all three antigens – have shown disappointing results attributed to an interference by the type 2 antigens in inducing typespecific immunity to types 1 and 3, weakening the effectiveness of the vaccine.
Wild poliovirus type 2, whose antigens are included in the trivalent vaccine, was last isolated in 1999, and is therefore a type 2 vaccine considered a less essential weapon in the fight to eradicate polio. Monovalent vaccines for types 1 and 3, while effective, have the drawback of complicating decision making about vaccine selection, Dr. Sutter and colleagues wrote (Lancet 2010 Oct. 26 [doi:10.1016/S0140- 6736(10)61230-5]).
For their research, Dr. Sutter and colleagues randomly assigned 900 newborns of healthy birth weight to one of five vaccine groups (about 180 patients per group); of these, 70 (8%) discontinued, leaving 830 for analysis. Parents and health care workers were blinded to vaccine allocation, and all five vaccines were supplied by Panacea Biotec, the designer of the study and one of its sponsors; samples were verified for potency at WHO collaborating laboratories in Europe.
The first dose of each vaccine was given at birth, when cord blood was also drawn; the second dose was administered at 30 days, after which more blood was taken, and at 60 days, final blood samples were drawn for analysis.
After two doses, seroconversion to poliovirus type 1 was 90% for monovalent type 1 and 86% for bivalent, compared with 63% for trivalent vaccine. Seroconversion to type 2 was 90% with monovalent type 2 vaccine, and 91% with trivalent vaccine. Conversion to poliovirus type 3 was 84% for monovalent and 74% for bivalent, compared with 52% for the trivalent vaccine.
The authors noted that because all the study sites were in southern and central India, one limitation of the study was in generalizing the findings to poliomyelitisendemic areas in northern India and elsewhere.
Nonetheless, the results, “confirmed that the bivalent vaccine leads to significantly more seroconversion than the trivalent vaccine,” the investigators said. Further, they wrote, the bivalent vaccine “will enhance individual and population immunity simultaneously for both poliovirus types 1 and 3, without any serious loss in immunogenicity” compared with monovalent vaccines.
Bivalent vaccine is already in wide use in India, the authors noted, “to increase population immunity against and accelerate the elimination of the final chains of transmission of these two remaining wild polioviruses, especially in areas where both poliovirus types 1 and 3 cocirculate.”
Yet while the bivalent vaccine covers both polio types known to be circulating, allowing for the eventual phasing out of effective trivalent vaccines, “a stockpile of [type 2 vaccine] should be kept once poliomyelitis eradication has been achieved to allow typespecific control measures should type 2 poliomyelitis be reintroduced,” the researchers wrote.
In an editorial comment, Dr. Nigel W. Crawford, MBBS, MPH, of the Royal Children’s Hospital in Melbourne, Australia called the bivalent vaccine “important for the poliomyelitis endgame” and said that it was likely responsible for the recent dramatic reduction in Indian polio cases, which were 32 in 2010, compared with 260 in 2009. However, Dr. Crawford also cautioned, WHO’s “plan of action for poliomyelitis eradication – with bOPV as the centerpiece – is only 50% funded for 2010-12.” (Lancet 2010 Oct. 26 [doi:10.1016/S0140- 6736(10)61427-4])
The study was funded by the GAVI Alliance, the World Health Organization, and Panacea Biotec. Two of its authors are employees of Panacea Biotec; no other conflicts of interest were reported.