New research from the BC Centre for Disease Control (BCCDC) seeks to improve the effectiveness of immunization programs for influenza, whooping cough, measles, mumps, rubella and more.
The research was presented at the recent 2018 Canadian Immunization Conference, a meeting on vaccines and their role in preventing infectious diseases across Canada. This year’s conference also commemorated the 100th anniversary of the Spanish Flu pandemic, which devastated the world immediately after the end of the First World War. In Canada, more than 50,000 people died during the 1918 pandemic.
At the time, the only vaccine routinely given was to prevent smallpox. Today, vaccines play a large role in preventing deaths from infectious diseases.
“Some diseases we’ve addressed through better sanitation, like typhoid and cholera,” said Dr. Monika Naus, medical director of Communicable Diseases and Immunization Service at the BCCDC. “Our water and food are safer now, but immunizations are foremost to prevent transmission of diseases spread by other means such as airborne spread, respiratory secretions and blood or body fluids.”
Prevent measles outbreaks with first dose of vaccine
In 2012, B.C. changed its vaccination schedule for measles, mumps and rubella (MMR) vaccine. Children continue to get their first dose at 12 months of age but the second dose is now combined with chickenpox vaccine and given when they enter kindergarten. The researchers found that this change resulted in a decline in adverse events following the vaccination that previously took place in the second year of life. However, it also resulted in a decline in the proportion of children who have received all their childhood doses of measles, mumps and rubella vaccine by age seven. The researchers believe this is because there is one less opportunity for immunization; formerly children who missed their second dose at 18 months of age could be caught up at school entry.
Dr. Naus, who led this research, said that the findings indicated that the major gap in immunity against measles is due to children not receiving a single dose of the vaccine. Any efforts to increase uptake of the MMR vaccine should focus on that first dose. About 90 per cent of people are completely protected after just one dose of the vaccine. The second dose is given to close that gap and reach that 10 per cent who did not develop immunity following the first dose.
Pneumococcal infection preventable in some high-risk-children
B.C. has had tremendous success in reducing the rates of a formerly common bacterial disease caused by Streptococcus pneumoniae bacteria through immunization but, there is still work to be done to provide highest-risk children with vaccines that offer enhanced protection. Invasive pneumococcal disease (IPD) is a bacterial infection that causes meningitis and sepsis; it can lead to serious complications and even death, and is more common in children with underlying conditions.
Children with chronic heart, lung, liver or kidney disease and several other conditions are eligible for additional vaccines that offer extra protection against IPD. The research revealed that between 2010 and 2014 in B.C., ten high-risk children under the age of five acquired an infection due to strains of the bacteria that were preventable by vaccine. Dr. Naus says efforts should be made to identify these children and ensure they get the appropriate protection. This could be done through improved communication between specialty care, primary care, and public health services and the parents of such children.
Mismatched influenza vaccine still affords protection
Most adults in B.C. receive a trivalent influenza vaccine (TIV) that protects against three kinds of influenza viruses including both influenza A subtypes (H3N2 and H1N1) but only one or the other influenza B lineage (Victoria or Yamagata). New research shows that the TIV reduces the risk of influenza B by at least 50 per cent most seasons, even when the lineage of influenza B circulating during flu season is different to the one contained in the vaccine. The only exception to this level of protection was when the influenza B strain in the vaccine was unchanged from the prior season. This research was presented by Dr. Danuta Skowronski, lead for the Influenza and Emerging Respiratory Pathogens Team at the BCCDC, and was recently published in the journal Clinical Infectious Diseases
BCCDC and Canadian investigators examine reasons behind low influenza vaccine effectiveness in 2017-18
Dr. Skowronski presented findings from the Canadian Sentinel Practitioner Surveillance Network (SPSN) that has revealed clues as to why North America’s 2017-18 influenza season was associated with one of the lowest estimates of vaccine effectiveness in more than a dozen years of monitoring by the SPSN.
During the 2016-17 and 2017-18 influenza seasons, Canada experienced back-to-back epidemics due to the H3N2 kind of influenza A virus. Through detailed epidemiological and genomic analysis of viruses collected by the SPSN, Dr. Skowronski and colleagues identified a number of factors potentially contributing to low vaccine protection in 2017-18. These factors include: repeat vaccination with an identical vaccine component across consecutive seasons, circulation of a dominant H3N2 variant able to evade population immunity, and mutations in the vaccine strain that accrued during the manufacturing process. These important clues to vaccine performance may lead to improvements in vaccine development and program design going forward.
Booster may reduce whooping cough risk but has minimal impact on disease rates in teens
The grade nine booster dose against pertussis, or whooping cough, may reduce the risk, but its overall impact on pertussis disease levels among adolescents was likely minimal, finds a new analysis.
In B.C., infants are immunized against pertussis before the age of one and then receive follow-up booster doses. Dr. Skowronski worked with colleagues in Quebec to analyze surveillance data spanning more than 20 years (1995 to 2017) in both provinces to assess the impact of an additional tetanus-diphtheria-acellular pertussis (Tdap) booster dose, introduced for grade nine students (generally age 14 and 15 years old) in 2004, on the subsequent risk of whooping cough in adolescents age 15 to 19 years old.
The researchers found that while the incidence of whooping cough in teens aged 15 to 19 years old was halved following introduction of the grade nine booster dose, they also observed that incidence in this age group was already lower than any other pediatric age group and showed decline from pre-teen levels even before the grade nine booster dose was introduced. This suggests the grade nine booster dose had little overall impact on pertussis disease levels in adolescents. They also found that a recent increase in pertussis incidence in teens aged 15 to 19 years old could be linked to the greater proportion who had received the acellular pertussis vaccine as infants, an issue also raised by researchers elsewhere. Together, these findings will inform potential adjustments to the pertussis vaccination schedule in B.C., Quebec and nationally.