Incidence Trends for SARS-CoV-2 Alpha and Beta Variants, Finland, Spring 2021.

Severe acute respiratory syndrome coronavirus 2 Alpha and Beta variants became dominant in Finland in spring 2021 but had diminished by summer. We used phylogenetic clustering to identify sources of spreading. We found that outbreaks were mostly seeded by a few introductions, highlighting the importance of surveillance and prevention policies.

Decrease of Rotavirus Gastroenteritis to a Low Level Without Resurgence for Five Years After Universal RotaTeq Vaccination in Finland.

BACKGROUND: Universal rotavirus (RV) vaccination with RotaTeq was introduced into National Immunization Programme (NIP) of Finland in September 2009. We have previously reported the reduction of RV gastroenteritis (GE) cases in the first 2 years after RV vaccination in NIP in Finland. METHODS: In Tampere University Hospital, a 2-year survey of acute GE (AGE) in children was conducted before NIP in the years 2006 to 2008. This was followed by a similar prospective survey in years 2009 to 2011 and now extended to years 2012 to 2014. Stool samples from children examined in the hospital for AGE were analyzed by real-time polymerase chain reaction assays for RV and norovirus, and positive samples were typed by sequencing. RESULTS: The proportion of RVGE of all AGE cases decreased from 52% (421 of 809 cases) in pre-NIP years to 26% (86 of 330 cases) in post-NIP years 2009 to 2011 falling to 12% (40 of 347 cases) in 2012 and 2014. The hospitalizations for RVGE were reduced by 90% and the outpatient clinic visits also by 90% in 2012 to 2014, compared with pre-NIP year; all AGE cases were reduced by 59%. Norovirus was a major causative agent of AGE in the post-NIP period, accounting for 34% of the cases in 2009 to 2011 and 29% in 2012 to 2014. CONCLUSIONS: RV vaccination in NIP has led to a major reduction of RVGE cases seen in hospital with no resurgence in 5 years after NIP. A high coverage of RV vaccination will maintain RV activity at a low level but not eliminate wild-type RV circulation.

Norovirus detection from sera of young children with acute norovirus gastroenteritis.

BACKGROUND: Antigenemia and viremia are common in rotavirus infection but only few studies have shown norovirus (NoV) RNA in the blood circulation. OBJECTIVES: To detect NoV RNA from serum of NoV-infected children and study if NoV RNAemia correlates with clinical severity of acute gastroenteritis. STUDY DESIGN: Serum specimens were collected from 176 Finnish children with acute NoV gastroenteritis. Semi-nested PCR was optimized to detect NoV capsid RNA from sera. NoV positive samples were further analyzed by sequencing. RESULTS: NoV RNA was found in 11/176 (6.3%) of serum specimens. NoV GII.4 was found in 8 cases and GII.3, GII.6 and GII.7 in one case each. The genotypes detected in serum were identical to findings in stools in all cases. Most of the NoV RNA detections in serum were in young children less than 18 months of age. The clinical features of NoV serum-positive cases were not different from NoV serum-negative cases. CONCLUSION: NoV RNA in serum is an uncommon finding limited to young children.

Genetic analyses of norovirus GII.4 variants in Finnish children from 1998 to 2013.

Noroviruses (NoVs) are the major causative agents of acute gastroenteritis (AGE) in outbreaks and in sporadic AGE in young children. Since the mid-1990s, NoV genotype GII.4 has been predominant worldwide. New GII.4 variants appear every two to three years, and antigenic variation is focused on the highly variable protruding domain (P2) of the NoV capsid protein which contains the receptor-binding regions. We studied NoV GII.4 variants in cases of endemic AGE in Finnish children from 1998 to 2013. Fecal specimens were collected from cases of AGE followed prospectively in rotavirus vaccine trials from 1998 to 2007, and from children seen at Tampere University Hospital because of AGE from 2006 to 2013. Partial capsid sequences were identified with RT-PCR and sequenced allowing P2 domain alignment and phylogenetic comparison of different GII.4 strains, with virus-like particles (VLPs) developed as candidate vaccines. Of 1495 NoV positive specimens 829 (55%) were of the GII.4 genotype, and altogether twelve GII.4 variants were identified. Identical GII.4 variants were detected in outbreaks of NoVs worldwide. A phylogenetic tree of the amino acid changes in the P2 region showed nine variants that arose over time. Our data indicates that GII.4 continues to be the predominant NoV genotype circulating in the Finnish community, and the changes in the P2 domain over time result in the development of new variants that cause AGE in children. Future NoV vaccines should either induce type specific immunity for each variant or, alternatively, induce broadly reactive protective immunity covering multiple variants.

Rotavirus antigenemia in children is associated with more severe clinical manifestations of acute gastroenteritis.

BACKGROUND: Rotavirus (RV) antigenemia and RNAemia are common findings in rotavirus-infected children. Sporadic associations between RV antigenemia and extraintestinal manifestations of RV infection have been observed. We examined the clinical severity of RV gastroenteritis in patients with and without RV antigenemia or RNAemia. METHODS: Stool, serum and whole blood samples were collected from children seen with acute gastroenteritis in Tampere University Hospital and studied for RV using reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay. Only exclusively RV-positive specimens were included into this study. The patients were divided into groups according to RV findings from stool, serum and blood specimens. Clinical manifestations were graded according to 20-point Vesikari scoring system. RESULTS: Of 374 children, 155 (41%) had RV in their stools. Of these 155 children, 105 (67%) were found to have RV RNA in the serum; of those, 94 (90%) had also RV enzyme-linked immunosorbent assay antigen. Thus antigenemia occurred in 61% (94 cases) of RV-infected children all of whom had concomitant RNAemia. Neither antigenemia nor RNAemia were detected in 85 patients with non-RV gastroenteritis. Patients who had RV RNA and RV antigen in both serum and stools were more likely to have a higher level of fever and more severe vomiting than patients who had RV only in stools. G1 genogroup RV was more often associated with RNAemia and antigenemia than other genogroups combined. CONCLUSION: Rotavirus antigenemia and viremia are commonly detected in children hospitalized for RV gastroenteritis and may be associated with increased severity of fever and vomiting.

Trivalent combination vaccine induces broad heterologous immune responses to norovirus and rotavirus in mice.

Rotavirus (RV) and norovirus (NoV) are the two major causes of viral gastroenteritis (GE) in children worldwide. We have developed an injectable vaccine design to prevent infection or GE induced with these enteric viruses. The trivalent combination vaccine consists of NoV capsid (VP1) derived virus-like particles (VLPs) of GI-3 and GII-4 representing the two major NoV genogroups and tubular RV recombinant VP6 (rVP6), the most conserved and abundant RV protein. Each component was produced in insect cells by a recombinant baculovirus expression system and combined in vitro. The vaccine components were administered intramuscularly to BALB/c mice either separately or in the trivalent combination. High levels of NoV and RV type specific serum IgGs with high avidity (>50%) as well as intestinal IgGs were detected in the immunized mice. Cross-reactive IgG antibodies were also elicited against heterologous NoV VLPs not used for immunization (GII-4 NO, GII-12 and GI-1 VLPs) and to different RVs from cell cultures. NoV-specific serum antibodies blocked binding of homologous and heterologous VLPs to the putative receptors, histo-blood group antigens, suggesting broad NoV neutralizing activity of the sera. Mucosal antibodies of mice immunized with the trivalent combination vaccine inhibited RV infection in vitro. In addition, cross-reactive T cell immune responses to NoV and RV-specific antigens were detected. All the responses were sustained for up to six months. No mutual inhibition of the components in the trivalent vaccine combination was observed. In conclusion, the NoV GI and GII VLPs combination induced broader cross-reactive and potentially neutralizing immune responses than either of the VLPs alone. Therefore, trivalent vaccine might induce protective immune responses to the vast majority of circulating NoV and RV genotypes.

Pre-existing immunity to norovirus GII-4 virus-like particles does not impair de novo immune responses to norovirus GII-12 genotype.

Noroviruses (NoVs) are one of the leading causes of acute nonbacterial gastroenteritis in humans of all ages. In the 1990s, NoV genotype GII-4 became responsible for the majority of NoV sporadic gastroenteritis cases and outbreaks worldwide. Vaccine development against NoV GII-4 is underway. At the same time, there is concern of new emerging NoV genotypes, such as GII-12, which has been recently associated with increasing numbers of NoV outbreaks worldwide. The specific question is whether type-specific pre-existing immunity to NoV GII-4 might impair cognate immune response induced by new viral infections or vaccines. Using GII-4 and GII-12 virus-like particles, we tested the impact of the immunity generated against NoV GII-4 on de novo antibody responses to GII-12 in mice. We found that pre-existing immunity to NoV GII-4 did not impair de novo immune response to the novel antigen, therefore suggesting lack of original antigenic sin (OAS).

Major reduction of rotavirus, but not norovirus, gastroenteritis in children seen in hospital after the introduction of RotaTeq vaccine into the National Immunization Programme in Finland.

UNLABELLED: Universal rotavirus (RV) vaccination is expected to reduce hospitalizations for acute gastroenteritis (GE) of children by eliminating most of severe RVGE, but it does not have any effect on norovirus (NV), the second most common causative agent of GE in children. After the introduction of the RV vaccine into the National Immunization Programme (NIP) of Finland in 2009, we conducted a prospective 2-year survey of GE in children seen in Tampere University Hospital either as outpatients or inpatients and compared the results with a similar 2-year survey conducted prior to NIP in the years 2006-2008. Compared with the pre-NIP 2-year period, in 2009-2011, hospitalizations for RVGE were reduced by 76 % and outpatient clinic visits were reduced by 81 %. NVGE showed a slight decreasing trend and accounted for 34 % of all cases of GE seen in hospital in pursuance of RVGE having decreased to 26 % (down from 52 %). In cases admitted to the hospital ward, RV accounted for 28 % and NV accounted for 37 %.The impact of RV vaccination was reflected as a 57 % decrease in all hospital admissions and 62 % decrease in all outpatient clinic visits for GE of any cause. CONCLUSION: RV vaccination in NIP has led to a major reduction of hospital admissions and clinic visits due to RVGE, but has had no effect on NVGE. After 2 years of NIP, NV has become the leading cause of acute GE in children seen in hospital.

Purification of norovirus-like particles (VLPs) by ion exchange chromatography.

Recombinant expression of the norovirus capsid protein VP1 leads to self-assembly of non-infectious virus-like particles (VLPs), which are recognized as promising vaccine candidates against norovirus infections. To overcome the scalability issues connected to the ultracentrifugation-based purification strategies used in previous studies, an anion exchange-based purification method for norovirus VLPs was developed in this study. The method consists of precipitation by polyethylene glycol (PEG) and a single anion exchange chromatography step for purifying baculovirus-expressed GII.4 norovirus VLPs, which can be performed within one day. High product purity was obtained using chromatography. The purified material also contained fully assembled monodispersed VLPs, which were recognized by human sera containing polyclonal antibodies against norovirus GII.4.

Production and characterization of virus-like particles and the P domain protein of GII.4 norovirus.

Noroviruses are an important cause of epidemic acute gastroenteritis in humans. In this study the production and characterization of GII.4 norovirus virus-like particles (VLPs) in insect cells is reported. Furthermore, the expression of corresponding norovirus polyhistidine-tagged P domain protein in Escherichia coli is described. The protruding P domain of the norovirus capsid is known to contain determinants for antibody and receptor binding. Therefore, P domain proteins were studied as an alternative diagnostic tool for evaluating norovirus infection. Analyses by dynamic light scattering and cryo-electron microscopy revealed the presence of intact VLPs with an average diameter of about 40 nm. Immunostaining and ELISA assays using norovirus-specific human sera revealed that VLPs and the P domain are recognized by norovirus-specific antibodies and by their putative receptor. The VLPs and P domain protein are potentially useful in the development of diagnostic and vaccination tools for noroviruses.

A comparison of immunogenicity of norovirus GII-4 virus-like particles and P-particles.

Norovirus (NoV) -derived virus-like particles (VLPs) resemble empty shells of the virus and NoV P-particles contain only protruding domains of the NoV capsid. Both NoV-derived subviral particles show similar functionality and antigenicity in vitro and are considered to be potential vaccine candidates against NoV gastroenteritis. BALB/c mice were immunized with baculovirus-produced GII-4 VLPs or the corresponding Escherichia coli-produced P-particles by the intramuscular or intradermal route and the NoV-specific antibody and T-cell immune responses were compared. Elevated antibody levels were induced with a single VLP immunization, whereas P-particle immunization required a boost. High avidity antibodies were raised only by VLP immunization. VLP immunization resulted in a balanced T helper type 1/type 2 immune response whereas P-particles induced a T helper type 2-biased response. Only VLP immunization primed T cells for interferon-γ production. Most importantly, cross-reactive B and T cells were induced solely by VLP immunization. In addition, VLP antiserum blocked the binding of heterotypic VLPs to human histo-blood group antigen receptor and saliva. The findings in this study are relevant for the development of NoV vaccines.

Norovirus VLPs and rotavirus VP6 protein as combined vaccine for childhood gastroenteritis.

Noroviruses (NoVs) and rotaviruses (RVs) are the two most important viral causes of severe gastroenteritis in young children worldwide. Live oral RV vaccines are already part of routine childhood immunization in many countries, but may be associated with low risk of intussusception and other potential risks associated with live vaccines. NoV capsid-derived virus-like particles (VLPs) are in early phase clinical trials, but there is no vaccine available yet. We suggest that there is a need for non-live vaccines against both enteric pathogens. We have combined NoV GII-4 VLPs and human RV recombinant VP6 (rVP6) protein produced by recombinant baculovirus (BV) expression system in insect cells and used this combination vaccine to immunize BALB/c mice parenterally. Strong systemic cross-reactive and cross-blocking antibody responses towards NoV and RV were induced, and there was no interference of the immune response to either antigen given in combination. Rather, we observed an adjuvant effect of rVP6 on the NoV-specific homologous and heterologous immune responses to genotypes not included in a vaccine formulation.

Noroviruses in children seen in a hospital for acute gastroenteritis in Finland.

UNLABELLED: Noroviruses (NoVs) are second only to rotaviruses (RVs) as causative agents of acute gastroenteritis (AGE) in children. The proportional role of NoVs is likely to increase after control of RV by vaccination. We investigated NoVs in children seen in Tampere University Hospital either treated as outpatients or hospitalized because of AGE before universal RV vaccination was implemented in Finland. This prospective study was conducted from September 2006 to August 2008. A total of 1,128 children <15 years of age with symptoms of AGE were enrolled either in the hospital clinic or in a ward, and stool samples for NoV studies were obtained from 759 children. NoVs were found in 196 (26%) cases. In the first year, NoVs were found in 116 (34%) out of 341, and in the second year, in 80 (19%) out of 418 cases. RVs were found respectively in 128 (38%) and 260 (62%) cases in these two seasons. Both RV and NoV were present in 24 cases. NoV genotype GII.4 predominated with a 96% share of the NoV cases in the first season and an 80% share in the second season. Other NoV genotypes seen infrequently were GII.7, GIIb, GI.6, GII.1, GII.2, and GIIc. The median clinical severity of NoV AGE was 14 compared to 16 for RV AGE on a 20-point scale. CONCLUSION: NoVs were nearly as common as RVs as causative agents of severe AGE in children seen in hospital. After implementing universal RV vaccination, the importance of NoVs will still increase further.

Norovirus GII-4 causes a more severe gastroenteritis than other noroviruses in young children.

Norovirus (NoV) GII-4 has emerged as the predominant NoV genotype in outbreaks of gastroenteritis worldwide. We determined clinical features of NoV GII-4 associated acute gastroenteritis (AGE) in comparison with AGE associated with other NoV types in infants during seasons 2001 and 2002. During the prospective follow-up period, 128 primary infections of AGE due to NoV were identified in 405 infants; of these, GII-4 was found in 40 cases (31%). NoV GII-4 was associated with longer duration of diarrhea and vomiting than other NoV genotypes, suggesting greater virulence of NoV GII-4.