Impact of Rotavirus Vaccine Introduction and Vaccine Effectiveness in the Republic of Moldova
Impact of Rotavirus Vaccine Introduction and Vaccine Effectiveness in the Republic of Moldova
Stela Gheorghita 2 3
Ludmila Birca 1 2
Ala Donos 0 2
Annemarie Wasley 2 6
Ion Birca 2 3
Radu Cojocaru 2 3
Anatol Melnick 2 3
Silviu Ciobanu 2 5
Liudmila Mosina 2 6
Margaret M. Cortese 2 4
Umesh D. Parashar 2 4
Ben Lopman 2 4
0 Chisinau Municipal Hospital for Children , Republic of Moldova
1 Chisinau City Infectious Diseases Hospital for Children
2 MS-A34 , Atlanta, GA 30333
3 National Center for Public Health
4 Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention , Atlanta , Georgia
5 World Health Organization Regional Office for Moldova , Chisinau
6 Vaccine-Preventable Diseases and Immunization, World Health Organization Regional Office for Europe , Copenhagen , Denmark
Background. The Republic of Moldova was the first low- to middle-income country in the World Health Organization European Region to introduce rotavirus vaccine (July 2012). We aimed to assess the impact of the rotavirus vaccine program and estimate vaccine effectiveness (VE). Methods. Surveillance for rotavirus gastroenteritis was conducted in 2 hospitals in the capital city of Chisinau starting in September 2009. Monthly rotavirus admissions by age were examined before and after introduction of rotavirus vaccination using interrupted timeseries analyses. We performed a case-control study of VE by comparing rotavirus case patients with test-negative controls. Results. Coverage with at least 1 dose of vaccine increased from 35% in year 1 to 55% in year 2 for children <1 year of age. The percentage of hospital admissions positive for rotavirus fell from 45% in the prevaccine period to 25% (rate reduction, 36%; 95% confidence interval [CI], 26%-44%) and 14% (rate reduction, 67%; 95% CI, 48%-88%) in the first and second years after vaccine introduction, respectively, among children aged <5 years. Reductions were most pronounced among those aged <1 year. Significant reductions among cohorts too old to be vaccinated suggest indirect benefits. Two-dose VE was 79% (95% CI, 62%-88%) against rotavirus hospitalization and 84% (95% CI, 64%-93%) against moderate to severe rotavirus. Conclusions. These results consistently point to profound direct and herd immunity impacts of the rotavirus vaccine program in young children in the Republic of Moldova. Vaccine coverage was modest in these early years following introduction, so there remains potential for further disease reductions.
Despite considerable progress, diarrheal disease remains the
fourth most common cause of mortality and second most
common cause of morbidity worldwide in children <5 years of age.
Rotavirus is associated with approximately one-third of all
severe diarrheal disease in young children, with recent estimates
of annual rotavirus-associated mortality ranging from 453 000
(2008) to 197 000 (2010) and 173 000 (2011) [
2009, the World Health Organization (WHO) has
recommended that rotavirus vaccines be included in national immunization
programs (NIPs) in every country and that introduction be
considered a public health priority. Two rotavirus vaccines are
licensed and used globally: monovalent Rotarix (RV1; Glaxo
SmithKline) and pentavalent RotaTeq (RV5; Merck and Co).
For both vaccines, clinical trials and postintroduction
evaluations have indicated a gradient of performance with vaccine
effectiveness (VE) ranging from approximately 70% to 100% in
high- and upper-middle-income countries to approximately
50% to 70% in lower-income settings in Africa and Asia [
With financial support from Gavi, the Vaccine Alliance,
rotavirus vaccination (RV1) was added to the Republic of
Moldova’s NIP in July 2012. Moldova was the first low- to
middleincome country in the WHO European Region to introduce
rotavirus vaccine. Vaccine is provided to all children through
the NIP at no cost through primary healthcare centers and
family doctor centers/offices. National guidelines stipulate that the
first dose of RV1 be administered between 2 and 3.5 months of
age and the second dose between 4 and 7 months of age.
Given that Moldova was the first country in the subregion to
introduce rotavirus vaccination, we aimed to assess the impact
of the program and to examine vaccine efficacy in the context of
spectrum of VE from other settings. Specifically, we aimed to
assess the impact of RV1 introduction on rotavirus-associated
hospitalizations and to determine the effectiveness of RV1 in
The Republic of Moldova is a low- to middle-income country in
the WHO European region and is a Newly Independent State of
the former Soviet Union. The total population of Moldova is
approximately 4 million, with an annual birth cohort of
approximately 43 000.
Sentinel surveillance for rotavirus gastroenteritis was
conducted in 2 hospitals, both of which are in the capital city of
Chisinau. The 100-bed Municipal Children’s Infectious
Diseases Hospital has conducted consistent surveillance since
September 2009. Mainly, children aged 1–5 years are admitted to this
hospital. To also capture infants aged <1 year, the 120-bed
Municipal Children’s Clinical Hospital No. 1 was added to the
surveillance system from January 2012.
We conducted surveillance for children with acute
diarrhea (defined as ≥3 loose stools in a 24-hour period and
with onset <7 days prior to the hospital visit) per
WHOrecommended protocol [
]. Surveillance was conducted 24
hours a day in the emergency department and inpatient
units where we aimed to enroll all children <5 years of age
who were admitted for diarrhea from the dates noted above
for the 2 hospitals. Nurses and physicians in the wards were
encouraged to notify the surveillance coordinator when
treating children with diarrhea. The emergency department
and hospital admission log was used to further identify any
child with a chief complaint of vomiting or diarrhea. Bulk
stool specimens were collected within 48 hours of admission.
Specimens were stored at 2°C–8°C prior to transfer to the
national laboratory on a weekly basis. Rotavirus testing was
conducted using a commercially available enzyme
immunoassay (ProSpecT; Oxoid, Cambridge, United Kingdom).
After written informed consent, basic demographic
information was collected. For cases, we also gathered information on
clinical characteristics, treatment, and course of illness through
face-to-face interviews with parents of cases and controls during
the hospital visit and review of medical records.
Vaccination history was obtained from records maintained at
the healthcare centers or family doctor offices where the child
was administered vaccine. Vaccination records at the clinic were
identified on the basis of participant name, sex, and date of
Vaccine Effectiveness Evaluation
We performed a case-control study of VE by comparing
vaccination status of rotavirus case patients with controls. Case
patients were identified by on-site study physicians and
nurses from the surveillance network described above. All
vaccine-eligible children (born on or after 1 May 2012) who
were hospitalized after 1 October 2012 for acute
gastroenteritis were enrolled and had their stool tested for rotavirus.
Given the age restrictions of rotavirus vaccination in
Moldova, we included only cases aged ≥6 months and excluded
children who were administered a dose of rotavirus vaccine
within 14 days of hospital admission. Controls were children
with acute diarrhea subject to the same inclusion criteria as
case patients but whose stool specimen tested negative for
Monthly rotavirus admissions by age were examined before
(September 2009–July 2012) and after (year 1: August 2012–
July 2013; year 2: August 2014–July 2013) introduction of
rotavirus vaccination using an interrupted time-series analyses. A
generalized linear model was fit to the time-series data,
assuming that monthly counts of admissions were Poisson distributed.
We adjusted for seasonality by including calendar month and
“hospital” and accounted for total diarrhea admissions by
considering the log-cases as the exposure. The rate ratio (RR) of
rotavirus admissions in the vaccine era was calculated using
an indicator variable for the year after rotavirus vaccine
introduction, with prevaccine time as the referent. We investigated
changes in rates by age groups (≤11 months, 12–23 months,
24–59 months) because vaccine coverage during the early
years of an immunization program and disease rates vary
substantially by age.
Our primary objective was to estimate VE of 1 or 2 doses of RV1
against rotavirus hospitalization. For secondary objectives, we
also estimated VE stratified by age (6–11 months and 12–23
months) and doses of vaccine received (1 only and exactly 2).
To investigate a potential gradient in protection by severity,
we repeated all analyses for VE against moderate to severe
rotavirus hospitalization, defined as hospital admission with
rotavirus detected in stool by enzyme immunoassay and with a
clinical severity score of ≥10 on a modified 20-point Vesikari
scoring scale [
To estimate VE, we fit unconditional logistic regression
models to calculate odds ratios of vaccination by rotavirus case
patient status, with associated 95% confidence intervals (CIs) [
All models controlled for age and hospital. VE was calculated as
(1 – odds ratio × 100%). Statistical significance was designated
as a P value <.05. Analyses were done with Stata software
version 13.0 (StataCorp, College Station, Texas).
Coverage with at least 1 dose of RV1 among rotavirus-negative
controls increased from negligible levels prior to vaccine
introduction (July 2012) to 20% in year 1 and 40% in year 2
postvaccination among children aged <5 years (Table 1). In children
aged <1 year, RV1 coverage increased from 35% in year 1,
reaching only 55% in year 2. Vaccination was generally timely, with
the first dose administered between the eighth and 15th weeks
of life for 88.3% of vaccinated children and the second dose
administered between the 16th and 35th weeks of life for 96.1% of
vaccinated children (Figure 1).
Rotavirus-associated hospitalizations decreased following
vaccine introduction (Table 1; Figure 2). In the first and second
years after vaccine introduction, the percentage of hospital
admissions positive for rotavirus fell from 45% in the prevaccine
period to 25% (RR, 0.64 [95% CI, .56–.74]) and 14% (RR, 0.33
[95% CI, .22–.52]), respectively, among those aged <5 years.
These patterns were most pronounced among children aged
<1 year, among whom rotavirus prevalence fell from 28% in
the prevaccine period to 14% (rate reduction, 79% [95% CI,
34%–64%]) and 6% (rate reduction, 73% [95% CI, 53%–84%])
in the first and second years postvaccination, respectively.
Rotavirus prevalence also decreased among children aged 12–23
months, from 48% prevaccine to 33% (rate reduction, 25%
[95% CI, 14%–35%]) and 13% (rate reduction, 75% [95% CI,
55%–86%]) in the first and second years postvaccination,
respectively, and decreased among children aged 24–59 months,
from 53% prevaccine to 33% (rate reduction, 32% [95% CI,
22%–41%]) and 22% (rate reduction, 55% [95% CI, 30%–
72%]) in the first and second years postvaccination, respectively.
Notably, significant reductions occurred among cohorts who
were too old to be vaccinated (age 12–59 months in year 1, and
age 24–59 months in year 2). In fact, the level of reduction (ie,
1 – RR) among all age groups in all postvaccination periods was
greater than vaccine coverage among controls, suggestive of
indirect benefits (Figure 3). In the prevaccine period and in
year 1 postvaccination, the median age of rotavirus cases was
20 months (interquartile range [IQR], 14–31 and 13–22
months, respectively), whereas in year 2 the median age was
23 months (IQR, 14–36 months) in the Municipal Children’s
Infectious Diseases Hospital, which consistently conducted
surveillance in 1- to 4-year-olds.
Vaccine Effectiveness From Case-Control Study
A total of 1433 children were enrolled in the case-control study,
of whom 995 (69%) were aged 6–23 months; 957 of these 995
children submitted a stool sample (96%), 857 of whom tested
negative (89.5%; controls) and 100 tested positive (10.5%;
cases) for rotavirus, among whom 67 (67%) were moderate to
severe cases. Of these remaining eligible children, documented
vaccine status was available for 914 (96%). Controls and cases
were similar in terms of age, proportion female, documented
vaccination status, and residence in Chisinau capital district;
controls had significantly lower severity score than cases (8.8
and 10.4, respectively, P < .001; Table 2).
Fifty-two percent of controls (422/819), 25% of cases (20/95),
and 16% (12/62) of moderate to severe cases received at least 1
dose of vaccine. Overall, VE with 1 or more doses was 75% (95%
CI, 58%–85%) against rotavirus hospitalization and 82% (95%
CI, 63%–91%) against moderate to severe rotavirus
hospitalization (Table 3). VE was higher for each incrementally higher
severity score (Figure 4).
VE for a full 2-dose course against rotavirus hospitalization
(79% [95% CI, 62%–88%]) appeared greater than a single dose
(60% [95% CI, 4%–85%]), though this difference was not of
statistical significance (P = .39). VE against rotavirus
hospitalization in the first year of life (84% [95% CI, 67%–92%])
appeared to be higher than in the second year of life (46% [95%
CI, −16% to 75%]), although this difference was not of
statistical significance (P = .23).
For all analyses, there was a nonsignificantly higher VE
against moderate to severe rotavirus compared to the VE against
rotavirus hospitalization. For example, VE for a full 2-dose
course against moderate to severe rotavirus hospitalization
was 84% (95% CI, 64%–93%) compared with 79% (95% CI,
62%–88%) against all rotavirus hospitalizations.
Moldova was the first WHO European Region country to
introduce rotavirus vaccination into its routine childhood
immunization schedule. These results consistently point to a profound
impact of the program on rotavirus disease in young children in
Chisinau, Moldova. VE of 2 doses was fairly high at 79% against
rotavirus hospitalization and 84% against hospitalization for
severe disease. Overall, rotavirus hospitalizations decreased by
two-thirds by the second year of the program in a pattern
consistent with vaccine impact. Decreases were greatest among
vaccinated cohorts—that is, children <1 year of age in the first year
and <2 years of age in the second year following vaccine
implementation. In addition, there were clear decreases in rotavirus
hospitalizations for all children <5 years of age, including
unvaccinated cohorts, strongly suggestive of indirect protection
resulting from infant immunization.
A strength of this study is the combination of surveillance
and case-control data, allowing us to examine both trends and
vaccine protection. We had 3 years of surveillance data prior to
vaccine introduction. Using this surveillance infrastructure, we
transitioned to perform a case-control study, principally by
adding the collection of vaccination history data from all eligible
enrolled subjects. Compared to community or hospital controls,
test-negative controls have the advantages of being
comparatively straightforward to recruit, having similar care-seeking
behavior as cases, and having less likelihood of bias in
ascertainment of vaccination status as the study team remains blinded to
the subjects’ case/control status.
There are some limits to the generalizability of these results.
First, our surveillance was restricted to the capital district of
Chisinau, where approximately one-quarter of the population
lives, so may not be representative of more rural parts of
Moldova. Second, we had limited data on hospitalization trends in
children aged <1 year. We added a second surveillance site at a
children’s hospital in January 2012 to have sufficient numbers
of subjects to evaluate VE in those aged <1 year, but had limited
historic data on trends in this age group. Third, the threshold
for hospital admission in Moldova and some other Newly
Independent States of the former Soviet Union may be lower, such
that mild cases are admitted who might receive outpatient care
in other healthcare systems. For this reason, we analyzed
vaccine efficacy for all rotavirus hospitalizations and moderate to
effect of vaccination would be a 41% reduction in disease rates
against severe disease. This VE is in line with estimates of
protection against hospitalization and severe disease in middle- to
high-income settings [
]. The lower VE in Moldova against all
rotavirus hospitalizations is consistent with the notion that less
severe cases are hospitalized in this country and that rotavirus
vaccines are most effective against severe disease [
It is well established that rotavirus vaccines are less effective
in low-income settings than in higher-income settings; however,
the specific reasons underlying this phenomenon are unclear.
Based on income, Moldova ranks below both El Salvador, Brazil,
Bolivia, and Colombia, but has a higher point estimate of VE
(82%) than any of these Latin American nations (76%, 40%–
77%, 72%, and −2%, respectively) [
]. Moldova’s 2-dose
RV1 VE estimate, especially against severe disease at 84% (95%
CI, 65%–93%), is highly consistent with vaccine efficacy estimates
from other low-mortality countries (in WHO mortality strata A
and B) where VE is 85% (95% CI, 80%–88%) based on pooled
analysis of 8 trials including >32 000 participants [
With 55% of the birth cohort vaccinated by the second
postvaccination year and overall VE of 75%, the maximum direct
(55% × 75%). However, we observed an average reduction over
the 2-year period of 61% among children aged <1 year and 52%
in those aged <5 years. Similarly, in the United States, in the
second year of vaccine impact, expected reductions based on direct
effects alone were 49% compared with observed reductions up
to 89%. Countries including the United States, El Salvador,
Australia, Austria, and Belgium have all observed reductions
in rotavirus hospitalizations in older, unvaccinated age groups
]. In most settings, these reductions have been noted for
children aged 24–59 months, but in Australia and the United
States there are data to suggest that these indirect benefits
extend to older children and adults [
14, 16, 18
]. Indirect protection
from rotavirus vaccination is a result of interruption of
transmission by reducing the incidence among infants, and thereby
reducing exposure of unvaccinated and/or older age groups to
In summary, we have observed a clear impact of the
introduction of rotavirus vaccination into the infant immunization
program of Moldova, and have measured robust VE. However, with
modest vaccine coverage (only reaching 55% in children aged
<1 year), there is potential for further reductions in disease.
This analysis has implications for Moldova as it is set to
“graduate out” of Gavi support eligibility and will increasingly be
responsible for financing of its national vaccination program.
These early impact data clearly argue for sustained use of
rotavirus vaccine, with further benefits possible with improved
coverage. These data should be encouraging for other countries in
the region considering introducing rotavirus vaccine into their
national programs. We recommend continued surveillance for
rotavirus gastroenteritis in Moldovan hospitals to monitor
severe cases separately. Indeed, we found a higher VE of 82%
vaccine uptake and to assess the medium- and long-term
benefits of rotavirus vaccination.
Acknowledgments. The authors thank Dovile Videbaek at the World
Health Organization Regional Office for Europe and Drs Olga Burduniuc,
Tatiana Juravlev, and Maria Ganea at the Municipal Children’s Infectious
Diseases Hospital and Children’s Clinical Hospital No. 1 in Chisinau,
Disclaimer. The findings and conclusions in this report are those of the
author(s) and do not necessarily represent the official position of the
Centers for Disease Control and Prevention (CDC). The views expressed by the
authors do not necessarily reflect the views of PATH, the CDC Foundation,
the Bill and Melinda Gates Foundation, or GAVI, the Vaccine Alliance.
Financial support. This work was supported by Gavi, the Vaccine
Supplement sponsorship. This article appears as part of the supplement
“Health Benefits of Rotavirus Vaccination in Developing Countries,”
sponsored by PATH and the CDC Foundation through grants from the Bill and
Melinda Gates Foundation and GAVI, the Vaccine Alliance.
Potential conflicts of interest. All authors: No reported conflicts. All
authors have submitted the ICMJE Form for Disclosure of Potential
Conflicts of Interest. Conflicts that the editors consider relevant to the content
of the manuscript have been disclosed.
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