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U.S. Department of Health and Human Services

Vaccines, Blood & Biologics

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Background on Study Results of U.S. Academic Researchers

What was the purpose of the study?

The research team used a powerful new method for studying viral DNA and RNA sequences in vaccines.  This method involves the use of microarray and high-throughput sequencing to characterize vaccine viral strains and determine if other viral sequences are present in the vaccine. 

What vaccines did the researchers test?

The researchers tested the following vaccines:

  • oral poliovirus (OPV, Bharat Biotech, India) – not licensed for use in the United States
  • rubella (Meruvax II, Merck and Co., Inc.) - no longer distributed in the United States
  • measles (Attenuvax, Merck and Co., Inc.) - no longer distributed in the United States
  • yellow fever (YF-Vax, Sanofi-Pasteur) - licensed by FDA for individuals 9 months of age and older who are living in or traveling to areas where yellow fever is endemic, or travelling internationally to countries that require evidence of vaccination from entering travelers
  • varicella-zoster virus or chickenpox (Varivax, Merck and Co., Inc.) - licensed by FDA for prevention of varicella (chickenpox) in individuals 12 months of age and older
  • rotavirus (Rotarix, GlaxoSmithKline) - licensed by FDA for the prevention of rotavirus gastroenteritis in infants
  • rotavirus (RotaTeq, Merck and Co., Inc) - licensed by FDA for the prevention of rotavirus gastroenteritis in infants
  • measles, mumps, and rubella (M-M-R II, Merck and Co., Inc) - licensed by FDA for the prevention of measles, mumps and rubella in individuals 12 months of age and older

In addition to the above vaccines, the researchers tested Pediarix vaccine specifically for PCV1, but they did not test for the presence of any other viral DNA or RNA.  Pediarix is licensed by FDA for the prevention of diphtheria, tetanus, pertussis (whooping cough), hepatitis B and polio for infants and children 6 weeks of age to 7 years.  Pediarix, which is not a live viral vaccine, is produced by GlaxoSmithKline.

What were the researchers’ findings?

In characterizing viral strains in several vaccines, the researchers did not find any unexpected variations.   An important finding was that an oral polio vaccine (manufactured in India, and not licensed for use in the United States) did not contain any sequences that are associated with the potential for the vaccine to cause a variant of poliovirus in a very small percentage of vaccinees.  Because oral polio vaccine is no longer used in the United States, this finding is of greater significance for people in other countries.

The researchers also found several virus sequences that were not related to the vaccine strains. Most of these were already known to be present in the vaccines or the cells used to produce them and have already been evaluated by FDA and determined not to pose a safety concern.  

However, one of the sequences found in the Rotarix vaccine, porcine circovirus 1 (PCV1), was not previously described or evaluated.  The research team also conducted several follow-up tests to confirm these results.

What did the researchers report about PCV1?

The researchers identified PCV1 DNA sequences in the oral Rotarix vaccine.

The researchers did not identify PCV1 DNA sequences in the RotaTeq vaccine, which is also licensed by FDA for the prevention of rotavirus disease. 

The researchers did not identify PCV1 DNA in any other of the tested vaccines.

The researchers concluded that the presence of PCV1 DNA in the Rotarix vaccine did not pose a safety risk.  FDA has also stated that there is no evidence at this time that DNA from PCV1 in Rotarix poses a safety risk.  PCV1 is not known to cause any disease in humans or other animals.  Rotarix has been extensively studied, before and after approval, and found to have an excellent safety record. 

What other viral sequences did the researchers detect?

The researchers found evidence of three other viral sequences in vaccines.  These do not represent infectious viruses.

The first was an avian leukosis virus (ALV)-like virus sequence, which is called EAV (for endogenous avian retrovirus), found in vaccines produced in cells derived from eggs (measles, M-M-R II, and YF-Vax).  EAV sequences are known to be present in all eggs and do not produce viruses that can grow in human cells.  EAV sequences in eggs were discussed at FDA advisory committee meetings in the mid 1990s, and determined not to pose any concerns for the safety of vaccines.

The second were DNA sequences for a simian endogenous retrovirus, with some similarity to a different monkey virus called SRV-1.  These were found in the Vero cell-produced vaccines (RotaTeq and Rotarix).  Additional analysis by the researchers concluded that these are sequences that occur naturally in the cell DNA, and are not able to produce a virus that can grow.  The cells used to produce these vaccines have also been tested by their manufacturers using assays for reverse transcriptase, which is a component of live retroviruses. The negative results in these assays provide strong additional assurance that live retroviruses are not present in these vaccines.

Third, the microarray study identified sequences similar to those of human endogenous retrovirus K (HERV-K) in vaccines produced in human cells (M-M-R-II, Meruvax II and Varivax).  These sequences are already known to be present in human cell DNA, and their identification is an expected finding, because these vaccines are known to contain human cell DNA as a result of the way they are manufactured.  It should also be noted that HERV-K sequences are not able to produce an infectious virus and therefore the presence of such sequences does not pose a safety concern in vaccines.

How do the findings of the research team affect FDA’s assessment of vaccines?

The safety and effectiveness of vaccines is one of FDA's top priorities.  FDA carefully evaluates the data it receives from manufacturers, as well as the most current science, to ensure that all licensed vaccines for the United States are safe and effective.

This research study used a powerful new technique to study vaccines and unexpectedly found the presence of PCV1 DNA in the rotavirus vaccine manufactured by GlaxoSmithKline.

PCV1 is not known to cause illness in humans, and there is no evidence that the presence of PCV1 poses any safety concern.  FDA is obtaining additional information about this finding and will provide updated information and recommendations to the public and clinical community soon.

As science and technology evolve and more advanced screening tools become available, FDA will need to carefully assess how these should be applied.  In this regard, FDA will be seeking the advice of experts whom we assemble when we convene an advisory committee meeting in the coming weeks.  

FDA is committed to keeping the public informed and assuring the safety of vaccines.