SAN FRANCISCO – Recent U.S. outbreaks of pertussis, influenza, and measles have revealed shifts in the diseases’ epidemiology, shifts that pose new prevention and management challenges, explained Yvonne Maldonado, MD, at the annual meeting of the American Academy of Pediatrics.
Routine immunizations prevent 33,000 child deaths a year in the United States, having reduced vaccine-preventable diseases by more than 90%, but outbreaks still occur, she said. The recent announcement that measles was eliminated from the Western Hemisphere, for example, doesn’t mean we won’t see cases, said Dr. Maldonado, vice chair of the AAP Committee on Infectious Diseases and chief of the division of pediatric infectious diseases at Stanford (Calif.) University.
Dr. Yvonne Maldonado
Dr. Maldonado reviewed specific challenges for flu, pertussis, and measles.
Influenza
The biggest challenges with controlling influenza are the failure to vaccinate children and the variable circulating strains each season, which can impact the performance of that year’s vaccine. Those changing strains and other factors also mean that the populations most at risk for serious complications also vary each season.
The two new mechanisms of change in influenza strains are antigenic drift and antigenic shift. Antigenic drift involves mutations that occur during repeated replications in the RNA strains of the virus, shifting its configuration over time so that it may not respond to the same antigens that the original strain responded to. Antigenic shift, however, is responsible for the periodic pandemics, when a complete genetic reassortment abruptly occurs because a new major protein from a strain jumps from an animal population into the human population, forming a new hybrid strain in humans.
Pertussis
Unlike flu, pertussis did become very uncommon because of widespread vaccination up until the early 2000s. But rates have begun to climb again, largely because of problems with the vaccine over time. Until the 1990s, the DTP vaccine, which includes a whole pertussis bacterium, was highly effective at preventing pertussis but could cause febrile seizures, an adverse event that proved too intolerable for many families.
It was replaced with the acellular pertussis vaccine DTaP, but research in the past 5-10 years has revealed that the effectiveness of DTaP and Tdap vaccines wanes much more quickly than anticipated. Subsequently, pertussis rates have almost continuously climbed from the early 2000s through the present, reaching an incidence of more than 100 cases per 100,000 among children younger than 1 year.
One of the biggest challenges now is improving vaccination rates among pregnant women, who were recommended in 2015 to get the Tdap vaccine in every pregnancy so that the newborn would have some passively acquired protection during the first few months of life.
Ongoing outbreaks then become exacerbated by pockets of lower vaccination rates among children in general.
Measles
The only chink in the armor against measles is failure to vaccinate against it, Dr. Maldonado said. Though the disease was eliminated from the United States in 2000, measles cases peaked recently in 2014, when 31 outbreaks involving 667 cases occurred because of imported cases from the Philippines. The next year, 60% of the 189 cases in 2015 resulted from the multistate measles outbreak starting at Disneyland in California.
Most of the individuals in both those years’ outbreaks were not vaccinated or had an unknown vaccination status. Of the 110 individuals with measles in California from the Disneyland outbreak, 45% were not immunized. Twelve were too young for vaccination, but 37 were eligible to have been vaccinated, and 67% of these were not vaccinated because of personal beliefs.
Vaccination rates for measles must be considerably higher, around 92%-94% of the population, to prevent outbreaks than for most other diseases, because the virus is so incredibly contagious.
“Measles is so infectious because it can exist in tiny microdroplets less than 5 mcg that can sit in the air up to 2 hours,” Dr. Maldonado explained. Yet only 92.6% of kindergartners had had both their MMR doses in 2014, compared with the peak of 97% between 2002 to 2007.
When children across all ages who have not received both doses of the vaccine are taken into account, 12.5% of all U.S. children and adolescents are currently susceptible to measles – and a quarter of those aged 3 years and younger are, Maldonado said.
The keys to preventing measles are high national coverage rates, an aggressive public health response (because early diagnosis can limit transmission), and improved implementation of health care worker recommendations.
“We have to keep measles in mind whenever we see fevers and rashes,” Dr. Maldonado cautioned. “Unfortunately, we see fevers and rashes all the time, so what really helps is a history of international travel or a parent with international travel.”
For families planning overseas travel, parents are recommended to give their infants the MMR as young as 6 months. But that dose does not count toward the child’s two doses recommended by the Centers for Disease Control and Prevention schedule.
“It’s a very tough call with measles, because we never know when it might pop up,” Dr. Maldonado said. “Measles will be sporadic, but when it happens, it’s a really big deal. You basically have to reach out to your entire patient log for several days before the child came in.”