The VSD, which is more specific and critical in its assessment, includes several health systems from different parts of the country. Scientists study the health records of patients in these systems to figure out whether a vaccine is causing the condition being reported by comparing the rates of the condition in people who did or didn’t get the vaccine. This allows them to determine whether the vaccine caused the problem. In the case of Rotashield, the VSD study found that infants who got the Rotashield vaccine were more likely to experience the intestinal blockage. While the VSD study was being done, use of the vaccine was stopped, and once the association was found, the vaccine was no longer used in the U.S. 

When additional studies were completed, Rotashield was found to cause about 1 in 10,000 to 1 in 30,000 children who got the vaccine to develop this intestinal blockage. If you think about that number, you realize that this system was capable of detecting a very rare occurrence. 

The next rotavirus vaccine was not approved for use in infants in the U.S. until 2006. 

The disease

What is rotavirus?

Rotavirus is a virus that infects the lining of the intestines. Most parents know rotavirus not by its name, but rather by its symptoms — high fever, repeated and forceful vomiting, and diarrhea. Infants are often sick for about a week, and they can become dehydrated because they can’t eat or drink without vomiting, which makes it very hard to get them the fluids that they need. 

By 5 years of age nearly all children have been infected with rotavirus. As a result, before we had a vaccine, rotavirus caused significant illness and need for medical care. Each year in the U.S.:

• 2.7 million children, usually between 6 months and 24 months of age, became ill
• 500,000 children went to the doctor because of rotavirus illness.
• 55,000 to 70,000 children were hospitalized.
• 20 to 60 children died.

The vaccine

How is the rotavirus vaccine made?

Two rotavirus vaccines are available in the U.S. Both are “live, weakened vaccines” given as droplets in the mouth: 

• RotaTeq, became available in 2006. It is made by using a rotavirus strain that infected a calf, which couldn’t cause disease in people. The calf virus was grown in the lab in a way that allowed it to mix with a human strain of rotavirus. The resulting viruses in the vaccine contain one protein from the human virus and the rest from the calf virus. In this manner, the vaccine virus causes immunity to the human proteins without making babies sick with rotavirus. This vaccine is given in three doses at 2 months, 4 months and 6 months of age.
• Rotarix became available in 2008. It is made from a rotavirus that infects people. By growing the virus in the lab in cells that were not human cells, the virus was weakened, so when given to babies, it cannot make them sick. This vaccine is given in two doses at 2 months and 4 months of age.

Does the rotavirus vaccine have side effects?

Since the first rotavirus vaccine was removed from use because it caused the rare intestinal blockage, studies of later rotavirus vaccines were much larger. This enabled scientists to look for the rare intestinal blockages found using the first rotavirus vaccine. In fact, clinical trials for the two current rotavirus vaccines combined included more than 130,000 babies. 

After the clinical trials were performed, and the vaccines were given to millions and millions of children, studies found that the intestinal blockage could still occur after vaccination. Nonetheless, these vaccines are still available. Here’s why:

• After the problem with the first rotavirus vaccine, scientists found that natural rotavirus infections can also cause intestinal blockages.  
• The intestinal blockages affected about 1 in 100,000 children who got the newer rotavirus vaccines, so they caused the condition less often than the first rotavirus vaccine.
• When rates of intestinal blockages were compared, those in vaccinated infants were similar to rates before vaccines were available. This meant that even if the vaccines were causing intestinal blockages, the risk following vaccination was not greater than the risk following natural rotavirus infections. 

Rotavirus vaccines are given before a child reaches 15 weeks of age, and all doses must be completed by 8 months of age, when children are most likely to experience a rotavirus infection.  

The rotavirus vaccines do not cause vomiting, diarrhea, fever, irritability or poor feeding when compared to those in babies who got the placebo during the clinical trials. 

Other questions you might have

Why was the rotavirus vaccine removed from the schedule in 1999 and then put back in 2006?

The first rotavirus vaccine, known as RotaShield, was approved for use in 1998. It was removed shortly thereafter because it was found to cause a rare form of intestinal blockage. This rare and painful condition occurs when the intestine folds into itself. This side effect of the vaccine was found to occur following about 1 of every 10,000 to 30,000 doses administered. Because RotaShield caused this side effect, it was removed from the recommended vaccine schedule and is no longer available in the U.S. 

Because almost every young child got rotavirus and about 1 of every 65 of them were hospitalized, the benefits of getting rotavirus vaccine clearly outweighed the risks. Therefore, when the new rotavirus vaccines became available in 2006 and 2008, this vaccine was added back to the U.S. infant immunization schedule.

Of note, Rotashield is still used in some other countries where the risk of death from dehydration caused by rotavirus is high due to limited access to medical care. In these places, the chance of having the intestinal blockage is much lower than the chance of death from rotavirus. While annual deaths in the U.S. from rotavirus were between 20 and 60 before a vaccine was available, rotavirus was a much more common cause of death for infants in other parts of the world. About 500,000 infants around the world were estimated to die each year from rotavirus before a vaccine was available.

Why is there a specific timing for the rotavirus vaccine?

The timing accounts for both the concerns around intestinal blockages and the period when babies are most susceptible to rotavirus infections:

• Intestinal blockages: Babies can experience intestinal blockages between 5 and 24 months of age, but they occur most frequently in infants between 5 and 9 months of age. So, the recommendations were designed to make sure the vaccine was started before babies reached the period when they might have a blockage from another cause, particularly since the blockages following vaccination are most likely after the first dose. So, this is why the vaccine must be started before a baby turns 4 months of age.
• Susceptibility to rotavirus: When babies are born, they have some protection from maternal antibodies, but those wane during the first few months of life. Since Rotateq came out before Rotarix and it required three doses for the best immunity, the recommendation was to give all of the doses before a baby reached 8 months of age. In this manner, a baby could develop their own immunity from vaccination before maternal antibody levels decreased to levels where they no longer afford protection.

Can the rotavirus vaccine cause bloody bowel movements in babies?

No, even when babies had diarrhea following receipt of rotavirus vaccine during clinical trials, their bowel movements weren't bloody. This makes sense because natural rotavirus infections do not cause bloody bowel movements either. 

Blood in a baby’s bowel movements can be caused by other types of infections, like Salmonella or Shigella, or by some health conditions related to the digestive tract. If you are seeing blood in your baby’s bowel movements, you should talk to their healthcare provider to figure out what might be causing it.

Do babies need all three doses of Rotateq since the other version only requires two doses?

Yes, the third dose increases the protection afforded by this vaccine. Remember that Rotateq and Rotarix are made from different types of rotaviruses. Since Rotateq includes rotaviruses that are mostly from a rotavirus strain that infects cows, the extra dose improves immunity. In the clinical trials, babies who got two doses of Rotateq (but didn’t yet get the third dose) had 84% fewer hospitalizations and emergency room visits for rotavirus. However, after three doses, these medical encounters were reduced by 94%-96%.

Relative risks and benefits

Do the benefits of the rotavirus vaccine outweigh the risks?

Before a rotavirus vaccine became available, between 55,000 to 70,000 children born in the U.S. were hospitalized with rotavirus each year. Use of the vaccine has decreased this number by about 80% (about 11,000-14,000 hospitalizations per year). While some infants may experience a rare intestinal blockage in the week after vaccination, the rates are not greater than those among unvaccinated infants. Other potential side effects were not greater in vaccinated compared with unvaccinated children. Therefore, the benefits of the rotavirus vaccine clearly outweigh the risks.

Disease risks

• Fever
• Vomiting and diarrhea
• Dehydration caused by severe vomiting and diarrhea can be fatal
• Rare intestinal blockage (about 1 in 100,000 infections)

Vaccine risks

• Rare intestinal blockage (about 1 in 100,000 doses)

Reference

Orenstein W, Offit PA, Edwards KM and Plotkin SA. Rotavirus vaccines in Plotkin’s Vaccines, 8th Edition, 2024, 1005-1024.

Reviewed by Paul A. Offit, MD, on Nov. 12, 2025