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About this publication
The report presents data from the resistance surveillance of viruses for 2020 and provides an overview of the use of antiviral agents in Norway. In addition, the report contains three chapters on current topics relevant to antiviral resistance:
- In light of the fact that new treatment principles are being applied against viral infections, the question is discussed: What is an antiviral drug?
- Surveilllance of resistance to HIV integrase inhibitors: Most treatment regimens used in first-line treatment of HIV infection contain an integrase inhibitor. Nevertheless, this class of drugs is not included in current HIV resistance monitoring.
- Overview of antiviral treatment strategies for SARS-CoV-2 from a virological perspective.
The usage of antivirals
According to The Norwegian Drug Wholesales statistics database, there has been an increase over the last few years in the sales of antiviral drugs measured in defined daily doses (DDDs). However, in 2020, this increase seems to have stagnated. There has been an increase in the usage of antiviral drugs against HIV, hepatitis B, and herpesviruses, and a reduction in the usage of drugs for treatment of hepatitis C. In spite of very low prevalence of influenza in the season 2020/2021, the sales of oseltamivir in 2020 was comparable to last year.
The sales of HIV drugs increased in 2020, but to a lesser extent than in 2019. The previous rise in number of persons treated has been mainly due to increased use of the fixed combination of emtricitabine and tenofovir disoproxil as Pre-Exposure Prophylaxis (PrEP), but in 2020, this increase has stagnated. When looking at complete treatment regimens, the use of single-tablet regimens is increasing. Combinations containing integrase inhibitors are widely used, which is also in accordance with the Norwegian guidelines.
There has been a very low incidence of influenza virus in the 2020/21 season due to extensive infection control measures for prevention of SARS-CoV-2. No resistance to oseltamivir or zanamivir was detected among the few influenza viruses tested this season.
Human immunodeficiency virus-1
The number of HIV infections in Norway reported in 2020 was lower than in 2019, and as expected, there was also a reduction in number of samples analysed as part of the resistance monitoring. Among the 75 samples from patients with newly diagnosed HIV-1 infection, resistance mutations were detected in 13.3% of the samples. This represents an increase compared to previous years. Among patients with detected resistance mutations, 50% were infected abroad.
Only one sample had a mutation that confers resistance to tenofovir or emtricitabine, the drugs used prophylactically as PrEP. Thus, there are currently no signals that indicate an increase in resistance to PrEP among newly diagnosed HIV-1 patients in Norway.
Hepatitis B virus
In 2020, 146 samples were analysed for hepatitis B virus (HBV) drug resistance mutations. Of these, 14 samples were from patients with treatment failure. The remaining 132 samples were from treatment naïve patients and can be considered surveillance of primary resistance.
Relevant drug resistance mutations were detected in only one of the 14 samples from patients on treatment, while no resistance mutations were detected in samples tested for primary resistance.
Human herpes viruses
In 2020, 30 samples were submitted to the reference laboratory for cytomelagovirus (CMV) for resistance testing. Out of the 20 samples, resistance mutations were detected in five samples. Although there has been an increase in the treatment of CMV infections in recent years, resistance mutations are only rarely detected. There is, however, no systematic resistance surveillance of CMV drug resistance, and the true prevalence of drug resistant CMV in Norway is therefore unknown.
Resistance mutations conferring resistance to aciclovir were detected in all of the four samples submitted for herpes simplex virus (HSV) drug resistance testing in 2020. One sample had an additional mutation which confer resistance to cidofovir. Despite increased usage of aciclovir, treatment failure is rare. As for CMV, there is no systematic surveillance of HSV drug resistance.
Detection of resistance mutations in all the analysed isolates indicates that an insufficient number of samples are submitted for resistance testing.
Hepatitis C virus
For the first time, data from drug resistance analyses of hepatitis C virus (HCV) in Norway are presented. A total of 21 samples from 2019 and 2020 have been analysed. The samples were from both untreated patients and patients with treatment failure but have not been systematically collected. Resistance data have been cross-referenced with epidemiological data from MSIS to enable comparisons of different subgroups.
Resistance associated substitutions were detected in 16 samples, seven of which were from patients with no history of previous treatment. A program for systematic surveillance of HCV drug resistance in newly diagnosed patients is being planned and will provide more representative data on the prevalence of resistance mutations in HCV infection in Norway.