Earlier Vaccinations Helped Limit Marine Adenovirus Outbreak

During an adenovirus (AdV) outbreak among recruits and staff at the Marine Corps Recruit Depot (MCRD) in San Diego, an investigation revealed that the earlier individuals working at the site received vaccination, the better. The clinical team found that accelerating the vaccination schedule could help prevent further outbreaks, medical separations, and training disruption.

From July 1, 2024, through September 23, 2024, a total of 212 trainees and staff developed AdV and 28 were hospitalized. Nine patients were hospitalized with AdV pneumo­nia within a 2-week period; 3 were admitted to the intensive care unit. Outpatient acute respiratory disease (ARD) cases also increased, with recruits accounting for nearly 97% of the AdV outbreak cases.

AdV is a frequent cause of illness among military recruits. Research has found that up to 80% of cases of febrile ARD in recruits are due to AdV, and 20% result in hospitalization. 

The military developed and implemented a live, oral vaccine against AdV serotypes 4 and 7 (most common in recruits) starting in the 1970s, reducing febrile respiratory illness in recruit training sites by 50% and AdV infection by > 90%. However, the manufacturer halted production of the vaccine in 1995. By 1999, vaccine supply was depleted, and ARD cases rose. A replacement vaccine introduced in 2011 proved 99% effective, leading to a dramatic 100-fold decline in AdV disease among military trainees. 

While the vaccine is effective, outbreaks are still possible among closely congregating groups like military trainees. AdV pneumonia cases spiked as the virus spread through the training companies and into new companies when they arrived at the MCRD in early July 2024. Most new infections were in recruits who had missed the AdV vaccination day.

Early symptoms of AdV may be very mild, and some recruits were likely already symptomatic when vaccinated. Aggressive environmental cleaning, separation of sick and well recruits, masking, and other nonpharmaceutical interventions did not slow the spread.

The preventive medicine and public health teams noted that AdV vaccination was being administered 11 days postarrival, to allow for pregnancy testing, and for assessing vaccine titers. US Department of Defense regula­tions do not dictate precise vaccination schedules. Implementation of the regulation varies among military train­ing sites. 

After reviewing other training sites’ vaccine timing schedules (most required vaccination by day 6 postarrival) and determin­ing the time required for immu­nity, the medical teams at MCRD recommended shifting AdV vac­cine administration, along with other standard vaccines, from day 11 to day 1 postarrival. Two weeks after the schedule change, overall incidence began declining rapidly.

Nearly 75% of patients had coinfections with other respiratory patho­gens, most notably seasonal coronaviruses, COVID-19, and rhinovirus/enterovirus, suggesting that infection with AdV may increase susceptibility to other viruses, a finding that has not been identified in previous AdV out­breaks. Newly increased testing sensitiv­ity associated with multiplex respiratory pathogen PCR availability may have been a factor in coinfection identification during this outbreak.

AdV is a significant medical threat to military recruits. Early vaccination, the investigators advise, should remain “a central tenet for preven­tion and control of communicable diseases in these high-risk, congregate settings.”

During an adenovirus (AdV) outbreak among recruits and staff at the Marine Corps Recruit Depot (MCRD) in San Diego, an investigation revealed that the earlier individuals working at the site received vaccination, the better. The clinical team found that accelerating the vaccination schedule could help prevent further outbreaks, medical separations, and training disruption.

From July 1, 2024, through September 23, 2024, a total of 212 trainees and staff developed AdV and 28 were hospitalized. Nine patients were hospitalized with AdV pneumo­nia within a 2-week period; 3 were admitted to the intensive care unit. Outpatient acute respiratory disease (ARD) cases also increased, with recruits accounting for nearly 97% of the AdV outbreak cases.

AdV is a frequent cause of illness among military recruits. Research has found that up to 80% of cases of febrile ARD in recruits are due to AdV, and 20% result in hospitalization. 

The military developed and implemented a live, oral vaccine against AdV serotypes 4 and 7 (most common in recruits) starting in the 1970s, reducing febrile respiratory illness in recruit training sites by 50% and AdV infection by > 90%. However, the manufacturer halted production of the vaccine in 1995. By 1999, vaccine supply was depleted, and ARD cases rose. A replacement vaccine introduced in 2011 proved 99% effective, leading to a dramatic 100-fold decline in AdV disease among military trainees. 

While the vaccine is effective, outbreaks are still possible among closely congregating groups like military trainees. AdV pneumonia cases spiked as the virus spread through the training companies and into new companies when they arrived at the MCRD in early July 2024. Most new infections were in recruits who had missed the AdV vaccination day.

Early symptoms of AdV may be very mild, and some recruits were likely already symptomatic when vaccinated. Aggressive environmental cleaning, separation of sick and well recruits, masking, and other nonpharmaceutical interventions did not slow the spread.

The preventive medicine and public health teams noted that AdV vaccination was being administered 11 days postarrival, to allow for pregnancy testing, and for assessing vaccine titers. US Department of Defense regula­tions do not dictate precise vaccination schedules. Implementation of the regulation varies among military train­ing sites. 

After reviewing other training sites’ vaccine timing schedules (most required vaccination by day 6 postarrival) and determin­ing the time required for immu­nity, the medical teams at MCRD recommended shifting AdV vac­cine administration, along with other standard vaccines, from day 11 to day 1 postarrival. Two weeks after the schedule change, overall incidence began declining rapidly.

Nearly 75% of patients had coinfections with other respiratory patho­gens, most notably seasonal coronaviruses, COVID-19, and rhinovirus/enterovirus, suggesting that infection with AdV may increase susceptibility to other viruses, a finding that has not been identified in previous AdV out­breaks. Newly increased testing sensitiv­ity associated with multiplex respiratory pathogen PCR availability may have been a factor in coinfection identification during this outbreak.

AdV is a significant medical threat to military recruits. Early vaccination, the investigators advise, should remain “a central tenet for preven­tion and control of communicable diseases in these high-risk, congregate settings.”

During an adenovirus (AdV) outbreak among recruits and staff at the Marine Corps Recruit Depot (MCRD) in San Diego, an investigation revealed that the earlier individuals working at the site received vaccination, the better. The clinical team found that accelerating the vaccination schedule could help prevent further outbreaks, medical separations, and training disruption.

From July 1, 2024, through September 23, 2024, a total of 212 trainees and staff developed AdV and 28 were hospitalized. Nine patients were hospitalized with AdV pneumo­nia within a 2-week period; 3 were admitted to the intensive care unit. Outpatient acute respiratory disease (ARD) cases also increased, with recruits accounting for nearly 97% of the AdV outbreak cases.

AdV is a frequent cause of illness among military recruits. Research has found that up to 80% of cases of febrile ARD in recruits are due to AdV, and 20% result in hospitalization. 

The military developed and implemented a live, oral vaccine against AdV serotypes 4 and 7 (most common in recruits) starting in the 1970s, reducing febrile respiratory illness in recruit training sites by 50% and AdV infection by > 90%. However, the manufacturer halted production of the vaccine in 1995. By 1999, vaccine supply was depleted, and ARD cases rose. A replacement vaccine introduced in 2011 proved 99% effective, leading to a dramatic 100-fold decline in AdV disease among military trainees. 

While the vaccine is effective, outbreaks are still possible among closely congregating groups like military trainees. AdV pneumonia cases spiked as the virus spread through the training companies and into new companies when they arrived at the MCRD in early July 2024. Most new infections were in recruits who had missed the AdV vaccination day.

Early symptoms of AdV may be very mild, and some recruits were likely already symptomatic when vaccinated. Aggressive environmental cleaning, separation of sick and well recruits, masking, and other nonpharmaceutical interventions did not slow the spread.

The preventive medicine and public health teams noted that AdV vaccination was being administered 11 days postarrival, to allow for pregnancy testing, and for assessing vaccine titers. US Department of Defense regula­tions do not dictate precise vaccination schedules. Implementation of the regulation varies among military train­ing sites. 

After reviewing other training sites’ vaccine timing schedules (most required vaccination by day 6 postarrival) and determin­ing the time required for immu­nity, the medical teams at MCRD recommended shifting AdV vac­cine administration, along with other standard vaccines, from day 11 to day 1 postarrival. Two weeks after the schedule change, overall incidence began declining rapidly.

Nearly 75% of patients had coinfections with other respiratory patho­gens, most notably seasonal coronaviruses, COVID-19, and rhinovirus/enterovirus, suggesting that infection with AdV may increase susceptibility to other viruses, a finding that has not been identified in previous AdV out­breaks. Newly increased testing sensitiv­ity associated with multiplex respiratory pathogen PCR availability may have been a factor in coinfection identification during this outbreak.

AdV is a significant medical threat to military recruits. Early vaccination, the investigators advise, should remain “a central tenet for preven­tion and control of communicable diseases in these high-risk, congregate settings.”