Identification of a recombinant live attenuated respiratory syncytial virus vaccine candidate that is highly attenuated in infants

J Infect Dis. 2005 Apr 1;191(7):1093-104. doi: 10.1086/427813. Epub 2005 Mar 1.


Background: Recombination technology can be used to create live attenuated respiratory syncytial virus (RSV) vaccines that contain combinations of known attenuating mutations.

Methods: Two live attenuated, recombinantly derived RSV vaccine candidates, rA2cp248/404 Delta SH and rA2cp248/404/1030 Delta SH, were evaluated in 31 adults and in 95 children >/=6 months old. rA2cp248/404/1030 Delta SH was subsequently evaluated in 44 infants 1-2 months old. These vaccine candidates share 4 attenuating genetic elements and differ only in a missense mutation (1030) in the polymerase gene.

Results: Both vaccines were highly attenuated in adults and RSV-seropositive children and were well tolerated and immunogenic in RSV-seronegative children. Compared with that of rA2cp248/404 Delta SH, replication of rA2cp248/404/1030 Delta SH was restricted in RSV-seronegative children (mean peak titer, 10(4.3) vs. 10(2.5) plaque-forming units [pfu]/mL), indicating that the 1030 mutation had a potent attenuating effect. Although rA2cp248/404/1030 Delta SH was well tolerated in infants, only 44% of infants who received two 10(5.3)-pfu doses of vaccine had detectable antibody responses. However, replication after administration of the second dose was highly restricted, indicating that protective immunity was induced. At least 4 of 5 attenuating genetic elements were retained in recovered vaccine viruses.

Conclusions: rA2cp248/404/1030 Delta SH is the first RSV vaccine candidate to be sufficiently attenuated in young infants. Additional studies are needed to determine whether rA2cp248/404/1030 Delta SH can induce protective immunity against wild-type RSV.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Amino Acid Substitution
  • Antibodies, Viral / blood*
  • Child, Preschool
  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / immunology
  • Double-Blind Method
  • Genes, Viral
  • Humans
  • Infant
  • Mutation, Missense
  • Respiratory Syncytial Virus Infections / prevention & control*
  • Respiratory Syncytial Virus Vaccines / administration & dosage
  • Respiratory Syncytial Virus Vaccines / adverse effects
  • Respiratory Syncytial Virus Vaccines / immunology*
  • Respiratory Syncytial Viruses / genetics
  • Respiratory Syncytial Viruses / immunology*
  • Respiratory Syncytial Viruses / physiology
  • Vaccines, Attenuated / administration & dosage
  • Vaccines, Attenuated / adverse effects
  • Vaccines, Attenuated / genetics
  • Vaccines, Attenuated / immunology
  • Vaccines, Synthetic / administration & dosage
  • Vaccines, Synthetic / adverse effects
  • Vaccines, Synthetic / immunology
  • Vaccines, Synthetic / virology
  • Viral Nonstructural Proteins / genetics
  • Viral Nonstructural Proteins / immunology
  • Virus Replication
  • Virus Shedding


  • Antibodies, Viral
  • Respiratory Syncytial Virus Vaccines
  • Vaccines, Attenuated
  • Vaccines, Synthetic
  • Viral Nonstructural Proteins
  • DNA-Directed RNA Polymerases