April 6, 2015

By: admin

By: Suzanne Canada, Ph.D.
Tanager Medical Writing

Concerns over outbreaks of potentially serious childhood diseases are in the news again in California with an increase in whooping cough infections in 2014, caused by the pathogen Bordetella pertussis, and a measles outbreak in December 2014 to February 2015.  Since outbreaks and epidemics may be infrequent, many of us do not realize that vaccine development is an ongoing process. Public health experts monitor changes in the predominant strains and pathogen virulence continuously.  Although the sudden upswing in cases is alarming for those with young children, fuller understanding of the cyclic nature of these outbreaks fosters refinements to public health practices as well as the vaccines.

Recent increases in the number of cases of pertussis infections are due to eroding immunity in the population of immunized individuals, as well as changes in the prevalent virulent strains.  Outbreaks of new strains or new agents occur every 6 months or so [1]. For example, every 4 or 5 years, a new increase in pertussis infections is observed [2]. However, development of safe and effective vaccines is a process that takes up to 15 years [1].  Therefore, health agency efforts must be ongoing and constant funding must be in place to have these vaccines ready when the public needs them.

Although we are observing outbreaks of whooping cough and measles in the past year, the rates of infection are still much lower than what was observed in the pre-vaccine era.  In the pre-vaccine era (prior to the 1940s in the USA), 157 serious pertussis infections occurred yearly per 100,000 cases, including ~15 infant deaths/100,000 cases [2].  The highest incidence recorded was 260,000 cases in 1934 [3]. Since the broad adoption of vaccinations, whooping cough is much rarer during most years; upswings were observed in California in 2010 and again in 2014.  In 2010, the most serious cases were seen among infants under one year old.  The experts then realized that they could best control the rate of serious infections in infants by immunizing mothers at G27-36 weeks or immediately after the birth [4], and by making sure everyone in the expectant family was also immunized.  Furthermore, the 2014 outbreak of whooping cough was highest among 15 year olds (137.8 cases/100,000) [2].  By gathering immunization records and analysis of blood samples for anti-pertussis antibodies among those who had an infection, the doctors deduced that eroding resistance to pertussis corresponded with the use of the acellular pertussis vaccine.

The acellular pertussis vaccine was developed in the 1990’s in response to a high rate of side effects (fever) in those receiving the whole cell vaccine.  The acellular vaccine uses a few especially prominent antigens (pertussis toxoid, filamentous heamagglutinin, and pertactin, among others) that are specific to all pertussis bacteria. In the late 1990s, the FDA recommended replacement of the whole cell vaccine with the acellular vaccine which doesn’t cause as much fever and discomfort following vaccination boosters.

Investigations of why the acellular pertussis vaccine is not conferring resistance as durable as others, such as the tetanus or diphtheria vaccines, are ongoing.  Some vaccine experts point to evidence that resistance to whooping cough isn’t as durable with the acellular vaccine [5, 6]; however, other analyses conclude that the genes encoding antigens targeted by acellular pertussis vaccines are changing at higher rates than other surface-protein encoding genes of the pathogen [7, 8].  A meta-analysis of different immunization schedules found that resistance depended on time since last immunization or exposure [9], with resistance dipping by 5 years after the last booster shot.  Some researchers have found that having more anti-pertussis antigens in the vaccine conferred a higher level of protection [10], and new antigens for the vaccine are under evaluation (e.g., LpxL 1 [11]).

Several virulence factors of B. pertussis are available for research purposes from List Labs including pertussis toxin (Products #179, #180 and #181), pertactin (Product #187), fimbriae 2/3 (Product #186), adenylate cyclase toxin (Product #188 and 188L),  filamentous heamagglutinin (#170) and lipopolysaccharide (Product #400). Inactivated toxins, known as toxoids, are frequently used in the vaccines.  List Labs offers toxoids of C. difficile toxins (Products #153 and #154), diphtheria toxin (Product #151), Staphylococcus aureus enterotoxin B (Product #123), tetanus toxin (Product #191) and botulinum neurotoxin types A and B (Product #133 and #139, respectively).  List Labs’ vaccine carrier proteins are provided for research use only; however, GMP material may be produced on a contract basis.  More information is available on our website: www.listlabs.com.

 

References

1. Rappuoli, R., Vaccines, Emerging Viruses, and How to Avoid Disaster. BMC Biology, 2014. 12: p. 100. PMID: 25432510
2. Winter, K., et al., Pertussis epidemic–California, 2014. MMWR Morb Mortal Wkly Rep, 2014. 63(48): p. 1129-32. PMID: 25474033
3. CDC, Pertussis Vaccination: Use of Acellular Pertussis Vaccines Among Infants and Young Children Recommendations of the Advisory Committee on Immunization Practices (ACIP) Morbidity and Mortality Weekly Review, 1997. 46: p. 1-25. PMID: 9091780
4. Raya, B.A., et al., Immunization of Pregnant Women Against Pertussis: The Effect of Timing on Antibody Avidity. Vaccine, 2015. 33(16):1948-52 PMID: 25744227
5. Silfverdal, S.A., et al., Immunological Persistence in 5 y olds Previously Vaccinated with Hexavalent DTPa-HBV-IPV/Hib at 3, 5, and 11 Months of Age. Hum Vaccin Immunother, 2014. 10(10): p. 2795-8.
   PMID: 25483640
6. Hara, M., et al., Pertussis outbreak in university students and evaluation of acellular pertussis vaccine effectiveness in Japan. BMC Infect Dis, 2015. 15(1): p. 45. PMID: 25656486
7. Sealey, K.L., et al., Genomic Analysis of Isolates From the United Kingdom 2012 Pertussis Outbreak Reveals That Vaccine Antigen Genes Are Unusually Fast Evolving. J Infect Dis, 2014. 212(2): p. 294-301. PMID: 25489002
8. Torjesen, I., Proteins Targeted by Pertussis Vaccine Are Mutating Unusually Quickly, Study Finds. BMJ, 2014. 349: p. g7850. PMID: 25552634
9. McGirr, A. and D.N. Fisman, Duration of Pertussis Immunity After DTaP Immunization: A Meta-analysis. Pediatrics, 2015. 135(2): p. 331-343. PMID: 25560446
10. Tefon, B.E., E. Ozcengiz, and G. Ozcengiz, Pertussis Vaccines: State-Of-The-Art and Future Trends. Curr Top Med Chem, 2013. 13(20): p. 2581-96. PMID: 24066885
11. Brummelman, J., et al., Modulation of the CD4(+) T cell response after acellular pertussis vaccination in the presence of TLR4 ligation. Vaccine, 2015. 33(12): p. 1483-91. PMID: 25659267