Epidemiological characterizations and clinical severity of
rotavirus infections
Children with RV1 were significantly younger [median age 3.2 (2.4,
3.8) vs 20.8 (14.6, 32.8) months old, (p<0.0001)], more
likely to be female (56.8% vs 38.9%, P =0.039), and to have mild
symptoms and overall disease severity than those with wildtype
G1P[8] (Table 2). Of all genotypes, RV1 was identified most
frequently in children under 3 months of age (~10% vs.
~1% for all others) (Figure 3). Children with the
emergent G12P[8] genotype were older (24-59 month) and more often
female (53.2% vs 38.9%, P =0.02) than those with wildtype
G1P[8] (Table 2; Figure 3). However, there was no increase in the
proportion of participants who were older during the 2017-2018 epidemic
season when G12P[8] caused the majority of rotavirus infections
(Figure S1). Children with G2P[4] were less likely to be
hospitalized (4.0% vs 15.1%; P =0.01) and had lower MVS scores
[14 (11, 16) vs 15 (12, 17); P =0.03] than those with
G1P[8](Table S1). With the exception of RV1 infection, children with
major rotavirus genotypes had similar clinical symptoms, management, and
disease severity scores (Table 2 and S1). Furthermore, co-infection with
other gastroenteritis viruses, enteric bacteria, or parasites in these
children did not result in different clinical characteristics (Table 2).
In unvaccinated children, AGE was most commonly due to the four
predominant genotypes each season: G1P[8], G2P[4], G9P[8],
and G12P[8] but not RV1 (Figure 4). RV1 was the predominant strain,
detected in more than 50% of children with AGE who had received 1 or 2
RV1 doses (Fisher’s exact test, P <0.001).
Discussion :
In the months preceding RV1 introduction, rotavirus G9P[8] was the
predominant genotype with a high percentage of G1P[8] strains also
detected. Following the implementation of a publicly funded RV1
vaccination program in Alberta with greater than 80% coverage(41), we
observed a large reduction in the percentage of AGE due to rotavirus
infections with the peak of activity diminishing during the 2015 to 2018
study years (Figure 2). While the circulating rotavirus genotypes
remained mostly unchanged, G9P[8] was no longer the prevailing
strain with the homotypic G1P[8], heterotypic G2P[4], and the
emerging G12P[8] strains becoming predominant.
Consistent with previous reports, we found that strain predominance
varies from year to year. However, more comprehensive multiyear data are
need to ascertain whether a delayed detection peak, a shortened duration
of the peak, or a shift from annual to biennial epidemics is observed
locally post vaccination introduction as documented in the US (42).
Controversy exists related to the long-term effect of vaccination on the
circulating genotype diversity (43). Whether the shift in rotavirus
genotype distribution in our study is due to natural fluctuations as
part of the inherent evolution of the virus, or to the emergence of new
vaccine-escape mutants due to selection pressure from RV1 remains to be
clarified.
The genotype constellation of the RV1 isolates found in our cohort
closely resemble the original RV1 virus. We did not identify any vaccine
and wild type rotavirus reassortments in the small number (n=4) of RV1
strains analyzed. Improved sensitivity of Illumina sequencing for low
viral load rotavirus samples is needed for future studies. RV1 strains
were associated with very mild AGE in infants under three months and
were detected in children who had received a single vaccine dose (19).
We could not differentiate between symptomatic infection by RV1 and
post-vaccine shedding of RV1 and incidental gastroenteritis symptoms in
these children.
G1P[8] was the predominant genotype reported previously in a
multisite genotype study, including Alberta, conducted under the
Canadian Immunization Monitoring Program, Active (IMPACT) (unpublished
data) in 2014 and 2015. In this study, we found that G9P[8] had the
highest prevalence in the short eight-month surveillance season of
2014-2015, comprising 31.9% of strains. The G9P[8] genotype was
first reported in the 1980s and has been widespread globally since the
mid-1990s, circulating as a minor type or predominant strain, accounting
for >70% of all rotavirus cases (17, 18).
Increases in G2P[4] prevalence have been reported in countries and
regions with consistent RV1 vaccine utilization (44), raising the
question of whether RV1 offers limited cross-protection against the
heterotypic G2P[4] strains since the genetic backbone (i.e. genotype
constellation) of the two (Wa-like vs DS1-like) are different. Although
we detected a transient increase in G2P[4] prevalence in the second
year following RV1 introduction, this must be interpreted cautiously as
the heterotypic G2 is often associated with cyclic re-emergence during
10-year periods (44). As such, it is not clear if the rise in G2P[4]
detection was due to vaccine selection pressure or simply reflecting the
natural oscillation of this genotype. A review of G2P[4] strain
evolution reported that alterations in G2P[4] distribution occur
commonly in countries that use RV1, RV5 or mixed vaccination strategies
as well as in countries without routine rotavirus vaccination (44). Our
data, support the global data (44) that there has not been a surge of
G2P[4] driven by vaccine selection pressure.
Strains of the G12 genotype were first described in infants with AGE in
southeast Asia in 1987 and 1998 (45, 46). Since then, the G12P[8]
genotype has been increasingly detected around the globe and gained
predominance as the sixth epidemic strain during the past few years (47,
48). In Alberta, G12P[8] strains first emerged in 2012 and became
predominant in 2018 according to provincial viral AGE surveillance data
(unpublished data). We found that G12P[8] predominantly infected
older children and was the most common strain in fully vaccinated
children. This suggests that G12P[8] may have unique epitopes that
evade host immune responses generated from vaccination or prior
infection by another rotavirus genotype. Thus, RV1 vaccine may provide
insufficient cross-protection against this emergent strain. Indeed,
multiple antigenic mismatches were identified in the VP7 (G protein) of
the predominant G12P[8] and the vaccine strains in the US (47).
Consistent with our results, G12P[8] infection was more common among
partially or fully vaccinated infants than other rotavirus genotypes.
However, an overall reduction in rotavirus activity occurred in
2017-2018 when G12P[8] predominated suggesting good protection of
RV1 against rotavirus AGE. Additional studies with longer surveillance
periods and larger sample sizes are warranted to understand vaccine
effectiveness against G12P[8]-specific rotavirus AGE.
Knowledge of the association between rotavirus genotype diversity and
AGE clinical severity is limited. Previous studies have presented
contradictory findings on this topic (18, 20-22). In our study, children
with RV1 detected in their stool specimens had less severe AGE episodes,
consistent with symptoms due to the live attenuated vaccine virus. We
also found that children with G2P[4] infections were less likely to
require hospitalization than those with G1P[8]. While the median MVS
score for children with G2P[4] infections was in the severe range
and clinical symptoms and other severity measures were comparable with
those of G1P[8], the median total MVS score was one point lower than
that of total rotavirus cases regardless of genotype. Our data suggest
that other than RV1 related G1P[8] isolates, the clinical severity
of different rotavirus genotypes did not differ significantly. Wild type
rotavirus of all genotypes detected were found to cause severe AGE in
young children thus emphasizes the need for rotavirus vaccines that
protects against all genotypes.
A limitation of our study is that the assay utilized was unable to
detect the new equine-like G3P[8] strains. Thus, future studies with
updated primer sets (49) are needed to obtain a more complete picture of
circulating rotavirus diversity. Moreover, as the rotavirus genotype
prevalence fluctuates naturally over a period that varies between 3 and
11 years (50), a longer surveillance period that includes additional
pre- and post-vaccine years is needed to fully understand the impact of
rotavirus vaccination on local rotavirus diversity.
In summary, our study revealed dynamic changes in rotavirus genotype
prevalence before and after RV1 introduction into Alberta’s routine
immunization program: G9P[8], G1P[8], G2P[4] and G12P[8]
predominated consecutively each season. This emphasizes the need for
ongoing monitoring of vaccine effectiveness against all genotypes as
most continue to be associated with severe AGE in children. Continued
rotavirus surveillance and detailed whole genome characterization of
strains could be employed to determine the changes in epidemiology and
distribution of rotavirus genotypes and to assess the potential impact
of vaccination selection pressure on rotavirus evolution in the post
vaccination era.