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An influenza outbreak due to A/USSR/77-like (H1N1) virus aboard a US Navy ship
Abstract:
An explosive outbreak of influenza caused by an A/USSR/77-like (H1N1) virus occurred aboard a US Navy ship in December 1977 and January 1978. Two hundred volunteers aboard the ship were studied. Virus was isolated from 36 of 57 patients from whom isolation was attempted. Among virologically confirmed patients, headache (97%), chills (92%), malaise (86%), and cough (75%) were the most frequent symptoms. There were two virologically confirmed cases with complications: one with collapsed lung and the other with pneumonitis. The study subjects were 25 years of age or less, but there was little influenza-like disease in members of the crew greater than 25 years of age. Prior vaccination with bivalent vaccine, containing A/NJ/76 (Hsw1N1) virus, did not offer significant protection against disease caused by A/USSR/77-like virus. Serologic tests, either or both complement fixation and hemagglutination inhibition, were positive in only 14 of 22 virologically confirmed cases, indicating a poor serologic response to primary infection with this strain of virus. These findings prevented calculation of meaningful disease to infection ratios. However, inapparent infection occurred in 3 of 19 (16%) individuals who denied having illness during the outbreak yet had serologic evidence of recent influenza infection.
Insights
An A/USSR/77-like (H1N1) influenza outbreak on a US Navy ship showed limited vaccine protection and poor serologic response in young adults. Many infections were inapparent, complicating disease-to-infection ratio calculations.
Area of Science:
- Epidemiology
- Virology
- Public Health
Background:
- Influenza outbreaks can spread rapidly in closed populations.
- Understanding strain-specific immune responses is crucial for vaccine development.
Purpose of the Study:
- To investigate an influenza A/USSR/77-like (H1N1) virus outbreak on a US Navy ship.
- To evaluate clinical symptoms, vaccine effectiveness, and serologic responses.
Main Methods:
- Virus isolation and identification from symptomatic individuals.
- Clinical symptom assessment and complication documentation.
- Serologic testing (complement fixation and hemagglutination inhibition) and analysis of inapparent infections.
Main Results:
- High attack rate of influenza-like illness in individuals ≤25 years old.
- Common symptoms included headache, chills, malaise, and cough.
- Prior vaccination with A/NJ/76 (Hsw1N1) vaccine provided no significant protection.
- Poor serologic response observed in confirmed cases; 16% of individuals without reported illness had serologic evidence of infection.
Conclusions:
- The A/USSR/77-like (H1N1) strain caused significant illness in young naval personnel.
- Existing vaccines were ineffective against this strain, and primary infection elicited a weak immune response.
- A notable proportion of infections were inapparent, highlighting challenges in disease surveillance.