The 2018 flu season, as tracked by the CDC, featured a potent mix of influenza A and B viruses that tested public health systems across the United States. This year highlighted the importance of timely vaccination, accurate surveillance, and clear communication during periods of elevated respiratory illness.
Below is a detailed overview of the 2018 flu season from the CDC perspective, followed by dedicated sections on vaccine effectiveness, surveillance methods, and guidance for clinicians and the public.
| Season | Dominant Viruses | Vaccine Match | Reported Burden |
|---|---|---|---|
| 2018–2019 | Influenza A(H3N2), B/Victoria lineage | Partial match for H3N2, good match for B | High outpatient ILI rates, increased hospitalizations |
| Surveillance Start | October 2018 | Annual vaccine composition reviewed in February | ILI outpatient visits tracked weekly |
| Peak Activity | February 2019 in most regions | Vaccination recommended before December | Pediatric and elderly hospitalizations elevated |
| Public Guidance | Annual vaccine, early antiviral use | LAIV usage guidance updated | Emphasis on high-risk groups |
Vaccine Effectiveness During 2018
Overall Estimates
CDC and partner studies estimated that the 2018-2019 influenza vaccine reduced the risk of medically attended acute respiratory infection by around 40 to 60 percent across age groups when the circulating strains were well matched. Effectiveness was higher against influenza B than against the drifted H3N2 variants, reinforcing the value of vaccination even in imperfect match years.
Age-Group Differences
In children and working-age adults, vaccine effectiveness appeared more consistent, while older adults showed lower absolute protection, partly due to age-related immune response changes. CDC stressed the need for higher-dose and adjuvanted vaccines for seniors to improve protection during seasons dominated by H3N2 strains.
CDC Surveillance and Data Methods
ILI and Laboratory Networks
Influenza-like illness (ILI) surveillance, based on outpatient healthcare provider reports, served as a primary signal for flu activity in 2018. This was complemented by virologic testing from collaborating laboratories, which helped identify circulating subtypes and lineage changes throughout the season.
Hospitalization and Mortality Tracking
The CDC FluSurv-NET network provided population-based hospitalization estimates, while mortality data from national vital statistics highlighted the greatest burden among older adults and young children. Together, these systems enabled timely updates to clinical guidance and risk communication.
Antiviral Use and Clinical Guidance
Early Treatment Recommendations
During 2018, CDC continued to emphasize rapid antiviral treatment for hospitalized patients and those at higher risk for complications, regardless of vaccination status. Oseltamivir and other neuraminidase inhibitors remained effective against both influenza A and B viruses detected that year.
Resistance Patterns
Ongoing surveillance showed low levels of antiviral resistance among circulating strains in 2018, supporting the use of neuraminidase inhibitors when indicated. These data helped inform clinician decision-making and reinforced confidence in the treatment algorithms published earlier in the decade.
Public Communication and Risk Messaging
Clear Messaging on Vaccine Value
CDC communicated that vaccination could still lessen symptom severity and reduce complications even when effectiveness against infection was moderate during the 2018 season. Messaging targeted both patients and providers to counter misconceptions and promote uptake before peak activity periods.
Addressing Misinformation
Efforts in 2018 focused on correcting myths about vaccine-induced illness and clarifying the benefits versus perceived risks. Social media campaigns and partnerships with community organizations helped amplify accurate information and reinforce trust in public health guidance.
Key Takeaways for Clinicians and Public Health
- Vaccination remains the most effective way to reduce flu-related hospitalizations and deaths.
- Antiviral medications are effective and should be started early in hospitalized patients and high-risk individuals.
- Age-specific vaccine strategies, including high-dose formulations, improve protection for older adults.
- Ongoing surveillance for strain changes and antiviral resistance supports timely clinical and public health decisions.
- Clear, evidence-based communication helps maintain public trust and vaccine uptake during challenging seasons.
FAQ
Reader questions
How well did the 2018 flu vaccine work against the circulating strains?
Overall vaccine effectiveness against medically attended respiratory illness was estimated at 40–60% during the 2018 season, with better protection against influenza B than against drifted H3N2 strains. CDC noted that vaccinated individuals who still got sick typically experienced milder and shorter illness.
Did the 2018 season include different flu types compared to previous years?
Yes, the 2018 season showed co-circulation of influenza A(H3N2) and influenza B viruses, with B/Victoria lineage becoming more prominent later in the season. This mix underscored the need for quadrivalent vaccines that cover both lineages.
What changes did CDC recommend for older adults during 2018?
CDC recommended higher-dose inactivated influenza vaccines and, where appropriate, the use of adjuvanted vaccines for adults aged 65 years and older, based on evidence of improved immune response and reduced hospitalization risk.
How did CDC monitor antiviral resistance in 2018?
Ongoing surveillance through domestic and international networks showed low levels of antiviral resistance among circulating influenza A and B viruses in 2018, supporting the continued use of neuraminidase inhibitors for treatment when indicated.