Study: Preterm Infants Less Likely to Be Fully Vaccinated

Lower Vaccination Rates Persist Into Early Childhood

September 04, 2019 02:28 pm Michael Devitt

Family physicians know all too well that children and infants who don't receive their vaccines on time can suffer serious health consequences. This is especially true for infants born prematurely, who are at increased risk for vaccine-preventable infections and related complications.

[infant about to receive vaccine]

With some exceptions, the CDC's Advisory Committee on Immunization Practices recommends(www.cdc.gov) that preterm infants -- defined as those born before 37 weeks' gestation -- who are clinically stable should get their vaccines at the same chronological age and using the same schedule as full-term infants. However, the results of a retrospective cohort study(pediatrics.aappublications.org) in the September issue of Pediatrics indicate that this often is not the case. The study found that more than half of all preterm infants still had not received the full complement of vaccines recommended by the ACIP by the time they turned 19 months old, and more than one-third remained undervaccinated at age 36 months.

Study Methods and Criteria

The study included more than 11,000 infants with birth hospitalizations at an urban academic medical center in Washington between 2008 and 2013. Hospital policy during the study period was to administer vaccines to all patients according to ACIP recommendations. To capture vaccine doses that may have been administered in other health care settings, the researchers linked data from the medical center with data from the Washington State Immunization Information System.

Story Highlights
  • A study recently published in Pediatrics found that more than half of all preterm infants had not received the full series of vaccines recommended by the Advisory Committee on Immunization Practices by age 19 months.
  • At age 19 months, only 47.5% of preterm infants had completed the recommended seven-vaccine series compared to 54% of full-term infants.
  • At age 36 months, more than one-third of children born preterm still had not completed the seven-vaccine series.

The main outcome measured was completion, by 19 months of age, of a seven-vaccine series consisting of

  • four doses of diphtheria, tetanus and acellular pertussis vaccine;
  • three doses of inactivated poliovirus vaccine;
  • one dose of measles, mumps and rubella vaccine;
  • three doses of Haemophilus influenzae type b vaccine;
  • three doses of hepatitis B vaccine;
  • one dose of varicella vaccine; and
  • four doses of pneumococcal conjugate vaccine.

The researchers also measured whether the seven-vaccine series was completed by 36 months of age, along with vaccination coverage for rotavirus, hepatitis A and seasonal influenza.

Of the 10,367 infants included in the sample, slightly more than 19% (1,991 infants) were considered preterm. The authors categorized these preterm infants into two groups: early (born between 23 and 33 weeks' gestation) and late (born between 34 and 36 weeks).

Results Depict Low Vaccination Rates

Although 54% of full-term infants completed the seven-vaccine series by 19 months, only 47.5% of preterm infants did so. When categorized by gestational age, completion rate was 46.4% in early preterm infants and 48.5% in late preterm infants.

As for vaccine coverage by type, a slightly higher percentage of preterm infants had received the requisite single doses of the MMR and varicella vaccines at 19 months than full-term infants. Overall, however, vaccination coverage was lower among preterm than full-term infants.

Across the board, a higher proportion of preterm than full-term infants missed doses in the seven-vaccine series. Ten percent of preterm infants were missing at least two vaccine doses, and 21.2% were missing four or more doses.

Although the percentage of children with full vaccination coverage increased with age, it remained lower in children born preterm. At 36 months, 71.3% of children born full-term had completed the seven-vaccine series compared with 63.6% of those born preterm.

Vaccination coverage for rotavirus, hepatitis A and influenza also were lower in preterm infants. At 19 months, less than 70% of preterm infants had received the rotavirus vaccine compared with more than 81% of full-term infants. At 36 months, however, hepatitis A and influenza vaccination rates among children born preterm were nearly identical to those born full-term.

Many Factors Likely Responsible

The authors wrote that multiple factors could explain why preterm infants remained undervaccinated, with parental concerns about vaccines a likely contributor.(www.ncbi.nlm.nih.gov) They cited one study(onlinelibrary.wiley.com) that showed some parents thought their preterm infant was not sufficiently well-developed to be vaccinated, as well as other research(www.ncbi.nlm.nih.gov) that showed many parents believed their preterm infants were medically vulnerable even after the infant's health had improved.

The authors noted that research focusing specifically on vaccine-related communication between health care professionals and parents with preterm infants is lacking, and they called for further investigation in this area. They also said more work is needed to devise effective strategies to improve vaccine coverage in preterm infants given the risks associated with undervaccination.

FP Vaccine Expert's Perspective

2018-2019 Vaccine Science Fellow Laura Morris, M.D., M.S.P.H., an associate professor in the Department of Family and Community Medicine at the University of Missouri School of Medicine in Columbia, was not surprised by the study's findings.

"It is disheartening, but not entirely surprising, to hear that complete vaccination rates were so low in both populations of children," she told AAFP News.

Morris said that when treating preterm infants, she often encounters parents who are concerned or hesitant about vaccines, which she addresses with a combination of clinical knowledge and personal experience.

"I will review the CDC and ACIP recommendations for vaccines with parents at a preventive care visit, so they have an opportunity to digest the vaccine schedule and ask questions, and I can respond to their concerns in person," she said.

"I also tell the story of my niece, born prematurely, who received her vaccines on time with the vaccine schedule. She had other health concerns, but my sister wisely chose to continue her vaccinations right on time."

Morris noted that FPs can use their expertise to anticipate and resolve any vaccine-related concerns parents of preterm infants may have.

"We should use our influence with families to give anticipatory guidance regarding immunizations -- during prenatal care, in visits for other family members, and at all well-child checks. Family physicians and their office staff members should provide consistent messaging regarding the safety and efficacy of vaccines, as well as express our well-founded confidence in the system of vaccine development, testing and safety."

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