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General information for researchers and lab and clinic staff. This page is not medical advice; treatment and isolation decisions belong to a clinician and to public-health guidance.
Short answer: what is neuraminidase?
Neuraminidase (NA) is an enzyme on the surface of influenza viruses. It is a sialidase: it removes sialic acids from cell receptors and from newly made viral surface proteins, which lets new virus particles leave the infected cell instead of clumping at its surface. Three antivirals (oseltamivir, zanamivir, peramivir) block it. Baloxavir does not; it acts on a different target.
Definition and scope
Neuraminidase is one of the two major glycoproteins on the influenza virion, alongside hemagglutinin (HA). The enzyme is a tetramer of four identical polypeptides. Each subunit has a cytoplasmic tail, a transmembrane region, a stalk and a catalytic head, and the head carries the enzyme’s active site. Reviews put NA at roughly 10-20% of the virion’s surface glycoproteins, with HA making up most of the rest.
The word also appears in bench work. Because NA is a sialidase, a name that describes a whole enzyme class, “neuraminidase” and “sialidase” are often used interchangeably in the literature. This page covers the influenza enzyme, its drug class and the laboratory measurements built around it.
How neuraminidase works
Neuraminidase works at the end of the infection cycle: it cleaves sialic acids from both cellular receptors and from the newly synthesized HA and NA on progeny virions. Without that cleavage, HA on new particles stays bound to receptors and the virions aggregate at the cell surface. The virus therefore depends on a functional balance between HA binding and NA cleaving.
Neuraminidase types
Avian influenza viruses carry nine NA subtypes, N1 to N9. They fall into two phylogenetic groups: group 1 holds N1, N4, N5 and N8, and group 2 holds N2, N3, N6, N7 and N9.
Neuraminidase versus hemagglutinin
| Feature | Neuraminidase (NA) | Hemagglutinin (HA) |
|---|---|---|
| Role in the cycle | Releases progeny virions by removing sialic acids | Works in balance with NA; binding is what NA cleavage releases |
| Enzyme? | Yes, a sialidase | Not an enzyme; the sialic acid-binding partner of NA |
| Subtypes in birds | Nine (N1 to N9), two groups | Not covered here |
| Share of surface glycoproteins | About 10-20% | Not covered here |
Source for the NA column and the balance concept: Frontiers in Microbiology 2019 review, “Influenza Virus Neuraminidase Structure and Functions” (read 2026-11-07).
Neuraminidase inhibitors and the baloxavir confusion
The CDC’s clinician summary lists six FDA-approved influenza antivirals, four of which are recommended in the United States. Three of those four are neuraminidase inhibitors; the fourth is not.
| Drug (brand) | Route | Target |
|---|---|---|
| Oseltamivir (Tamiflu) | Oral | Viral neuraminidase |
| Zanamivir (Relenza) | Inhaled | Viral neuraminidase |
| Peramivir (Rapivab) | Intravenous | Viral neuraminidase |
| Baloxavir marboxil (Xofluza) | Oral | Cap-dependent endonuclease; interferes with viral RNA transcription |
Source: CDC, clinician summary of influenza antiviral medications (read 2026-11-07). Oseltamivir, zanamivir and baloxavir are active against influenza A and B; peramivir’s efficacy data come mainly from influenza A trials, with few influenza B subjects. The CDC does not recommend amantadine or rimantadine because of high levels of resistance among circulating influenza A viruses. The common mix-up is to call baloxavir a neuraminidase inhibitor; by the CDC’s description it is not.
Where it matters for labs and surveillance
- Activity assays. The literature describes fluorometric NA activity assays. Calcium raises NA activity, and elution tests compare 4 C with 37 C because NA is inactive at 4 C.
- Resistance. A single change, H275Y, conferred oseltamivir resistance in H1N1 viruses in 2007-2008 and spread globally, which is why surveillance programs track antiviral susceptibility. See the CASRAI guides on NREVSS and sentinel surveillance, and the dictionary term GISAID for sequence sharing.
- Related lab methods. Infectivity and release are also studied with cell-culture methods such as the plaque assay. Work with live influenza viruses is governed by biosafety level; see biosafety levels BSL-1 to BSL-4.
Common misunderstandings
- “All influenza antivirals are neuraminidase inhibitors.” Baloxavir is a cap-dependent endonuclease inhibitor.
- “There is one neuraminidase.” There are nine avian subtypes in two groups, and the enzyme is a tetramer of identical subunits.
FAQ
What is neuraminidase?
An influenza surface enzyme (a sialidase) that cleaves sialic acids so new virions can detach from the infected cell.
What are some examples of neuraminidase inhibitors used to treat influenza?
Oseltamivir (oral), zanamivir (inhaled) and peramivir (intravenous), per the CDC clinician summary. Baloxavir is an influenza antiviral but not a neuraminidase inhibitor.
Do I need to isolate if I have influenza B?
This page gives no individual advice. Influenza A and B both cause seasonal disease. Oseltamivir and zanamivir are active against both; peramivir’s efficacy data come mainly from influenza A trials (CDC). Isolation recommendations depend on the setting and are set out in CDC guidance and by your clinician or employer’s infection-prevention staff.
What is the deadliest type of influenza?
The sources behind this page do not rank influenza types by lethality, so no ranking is given here. Severity varies by season, circulating subtype and the patient; the CDC’s influenza pages are the place to check current data.
Sources
- CDC, Influenza antiviral medications: summary for clinicians, https://www.cdc.gov/flu/hcp/antivirals/summary-clinicians.html (read 2026-11-07).
- Frontiers in Microbiology (2019), Influenza Virus Neuraminidase Structure and Functions, https://pmc.ncbi.nlm.nih.gov/articles/PMC6362415 (read 2026-11-07).
