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Updated: May 26, 2026
Influenza A Virus Studies in a Mouse Model of Infection
Published on: September 7, 2017
No evidence of murine leukemia virus-related viruses in live attenuated human vaccines
William M Switzer1, Haoqiang Zheng, Graham Simmons
1Laboratory Branch, Division of HIV/AIDS Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. bswitzer@cdc.gov
Background:
The association of xenotropic murine leukemia virus (MLV)-related virus (XMRV) in prostate cancer and chronic fatigue syndrome reported in previous studies remains controversial as these results have been questioned by recent data. Nonetheless, concerns have been raised regarding contamination of human vaccines as a possible source of introduction of XMRV and MLV into human populations. To address this possibility, we tested eight live attenuated human vaccines using generic PCR for XMRV and MLV sequences. Viral metagenomics using deep sequencing was also done to identify the possibility of other adventitious agents.
Results:
All eight live attenuated vaccines, including Japanese encephalitis virus (JEV) (SA-14-14-2), varicella (Varivax), measles, mumps, and rubella (MMR-II), measles (Attenuvax), rubella (Meruvax-II), rotavirus (Rotateq and Rotarix), and yellow fever virus were negative for XMRV and highly related MLV sequences. However, residual hamster DNA, but not RNA, containing novel endogenous gammaretrovirus sequences was detected in the JEV vaccine using PCR. Metagenomics analysis did not detect any adventitious viral sequences of public health concern. Intracisternal A particle sequences closest to those present in Syrian hamsters and not mice were also detected in the JEV SA-14-14-2 vaccine. Combined, these results are consistent with the production of the JEV vaccine in Syrian hamster cells.
Conclusions:
We found no evidence of XMRV and MLV in eight live attenuated human vaccines further supporting the safety of these vaccines. Our findings suggest that vaccines are an unlikely source of XMRV and MLV exposure in humans and are consistent with the mounting evidence on the absence of these viruses in humans.
Insights
No evidence of xenotropic murine leukemia virus (XMRV) or MLV was found in eight live attenuated vaccines, supporting vaccine safety. These findings suggest vaccines are an unlikely source of XMRV and MLV exposure in humans.
Area of Science:
- Virology
- Vaccinology
- Molecular Biology
Background:
- The association of xenotropic murine leukemia virus (MLV)-related virus (XMRV) with diseases like prostate cancer and chronic fatigue syndrome is controversial.
- Concerns exist regarding potential contamination of human vaccines with XMRV and MLV.
- Live attenuated vaccines are widely used globally, making their safety profile critical.
Purpose of the Study:
- To investigate the presence of XMRV and MLV in eight common live attenuated human vaccines.
- To identify any other adventitious viral agents in these vaccines using deep sequencing.
Main Methods:
- Eight live attenuated human vaccines were tested for XMRV and MLV using generic PCR.
- Viral metagenomics via deep sequencing was employed to detect other potential viral contaminants.
- Specific PCR assays were used to detect residual DNA and RNA from production cell lines.
Main Results:
- All eight vaccines tested were negative for XMRV and closely related MLV sequences.
- Residual hamster DNA, containing novel endogenous gammaretrovirus sequences, was detected in the Japanese encephalitis virus (JEV) vaccine.
- Metagenomics analysis did not identify any adventitious viral sequences of public health concern.
- Sequences consistent with Syrian hamster cell line origin were found in the JEV vaccine.
Conclusions:
- The study found no evidence of XMRV and MLV contamination in the tested live attenuated vaccines.
- These findings support the safety of the evaluated vaccines.
- Vaccines are unlikely to be a source of XMRV and MLV exposure in the human population.
