Professor Dr. Helen Chu discusses recent changes to vaccine recommendations (Photo by Elizar Mercado).
In June 2025, all voting members of the Advisory Committee on Immunization Practices, a body that makes recommendations to the Centers for Disease Control and Prevention for vaccine use in the U.S., were dismissed. This included Helen Chu, professor of epidemiology at the University of Washington School of Public Health and professor of medicine - allergy and infectious disease at UW Medicine in Seattle.
With this change in the voting members has come changes in vaccine recommendations. These changes are met with concerns from former ACIP members like Chu about if the ACIP will follow its standard for scientific rigor to evaluate vaccine safety and efficacy and make evidence-based recommendations for vaccine delivery. Chu, an expert in immunizations who has led the Seattle Flu study for years, reflects on what Americans can expect from some of these changes.
“A change to the way that we review vaccines, in a way that we look at the evidence around its safety and its effectiveness, has a substantial impact on the health of Americans,” Chu said.
This written interview has been lightly edited for length and clarity.
What should people know about changes to the Advisory Committee on Immunization Practices, their policies and updated vaccine recommendations?
Helen Chu: The Advisory Committee on Immunization Practices (ACIP) was founded in 1964 and has been in place for over six decades. The point of this committee was to make recommendations to the CDC for use of vaccines in the United States. One of the main things it does is it reviews the data and helps decide which vaccines are recommended, and therefore, which vaccines are paid for by health insurance companies and often by the federal government, particularly for children without health insurance.
Up until last month, I was one of 17 voting members of the ACIP. Last month, all current members of the ACIP were dismissed and replaced with new members who have made new vaccine recommendations for use in the United States. We're at a time right now where we're trying to determine what is the best next step in terms of science-based vaccine recommendations. Do we follow the federal guidelines, or do we need to turn to other organizations who may be able to provide science-based recommendations for use of vaccines?
As the ACIP has changed its membership and switched to a panel with individuals who may have different views on vaccine safety in the United States, the recommendations will change. One of the key decisions this past month was the committee’s vote on the use of thimerosal in multi-dose flu vaccines. Thimerosal is a safe preservative used in these vaccines to prevent bacterial growth. As a result of the ACIP decision, vaccines that contain thimerosal are no longer recommended for use in the United States. Therefore, you can't give or purchase multi-dose vaccines anymore. That really impacts places like nursing homes, where older adults need vaccines. Often, they deliver them using these multi-dose vials. People who are in nursing homes, who need vaccines now, need a different way to get their multi-dose flu vaccines.
That's one example of how this new panel has already changed the way we're going to administer vaccines in the U.S.
How has safety and efficacy research historically informed ACIP's approach to evidence-based recommendations for immunizations?
The way that ACIP historically works is that it reviews the data from before the vaccine is licensed. That’s the clinical trial data where we look at the adverse events and the safety of the vaccines when they were studied, and then also after its license. So, after the vaccines are approved for use in the United States, the ACIP reviews all of the data that comes in from various research institutions, for example, Kaiser Permanente, and they see the population-level data and make sure that it remains safe when it's rolled out to the general public.
This happens regularly. So, before the vaccine is licensed, we look at the clinical trial data and we use that to make decisions. Then after the vaccine is licensed, we review on a very regular basis, particularly right after the vaccines are licensed, to make sure that the vaccines continue to be safe. If we find something that is concerning, then we change our recommendations to reflect this.
How have these science-backed recommendations from ACIP historically impacted the health and wellbeing of Americans? What is the risk of new recommendations that may lower vaccination rates?
The ACIP recommendations are the backbone of insurance payments for vaccines in the United States. They form the schedule for vaccines – the appropriate ages and timing to deliver vaccines – that are recommended for use for adults and children. It impacts the people who get it paid for from private health insurance. It also impacts what is covered through a program called Vaccines for Children, which covers half the children in the United States.
Every vaccine that's recommended for use has been shown to be safe and effective and to save lives. A change to the way that we review vaccines, in a way that we look at the evidence around its safety and its effectiveness, has a substantial impact on the health of Americans.
What should people know about the childhood vaccine schedule and its safety?
What we know now is that the current childhood vaccine schedule has been highly optimized to reduce the number of doses that children have to receive. It aligns with the recommended pediatric wellness visits, so it minimizes the number of times children need to come into a doctor’s office. One of the concerns from some members of the public and anti-vaccine movement that has come up with the childhood vaccine schedule is the amount of times people or children are getting vaccines and the number of vaccines that they're getting.
One of the important things to realize is that though the number of diseases that you're protected against has increased, the amount of foreign substance that you're getting as part of each vaccine is actually much lower than, say, in the 1960s or the 1950s, because the vaccines are just better. They're cleaner. They have less side effects that contain small pieces of the virus, or the bacteria are much smaller pieces than they used to contain.
Vaccines protect you by exposing you to much less than in the past. The amount of side effects that we see with childhood vaccines has gone down significantly. As time has passed and as vaccine technology has improved, right now the concern, I think, from the new ACIP, and I can't really speak for them, but, I think is that they want to reduce the number of childhood vaccines that children are getting at each visit, either to space them out or to eliminate them completely.
What will happen if you do this? The main example I would use right now is the measles vaccine. There is a measles outbreak that's happening across the United States where we are at risk of losing our measles elimination status in the United States. There is a concern, by the anti-vaccine community that measles vaccines are associated with autism. [Many peer reviewed, robust studies of large populations have found no link between vaccines and autism] I think that is driving a lot of this conversation about getting MMR vaccine as a child.
I think potentially what could happen is that this skepticism about MMR and potentially a change to the vaccine schedule, where MMR is either made optional or allowed to be delayed until later, or spaced out further, those all have the direct consequence of making fewer people immune to measles, both immediately, and then also, decreasing the herd immunity that we have to prevent more vulnerable people from getting measles.
What are potential impacts to society if we were to lose our measles elimination status?
I think we're already seeing the impact to loss of measles containment in the United States, as we've seen measles cases increase and ongoing local transmission of measles. What has happened is that children are getting sick, but also the people around them are getting sick. I think people have forgotten how bad measles can be when you're a child: not only does it have short-term consequences of making you very sick with pneumonia, with the infection of your brain, and with all sorts of other things that can happen immediately, it also has long-term consequences, such as making your immune system not work as well and not responding to other diseases. You can also get a measles infection that shows up five to 10 years later.
The other things we worry about are obviously the people who live with kids with measles. Even if a child gets measles and gets a fairly mild case, they can still infect a pregnant woman in the household or their older family member, or someone who's immunocompromised who happens to be in the same classroom as them. Those people don't have the ability to control their measles infection, and they can get quite sick and maybe die.
What are the financial consequences of losing containment of vaccine-preventable diseases in the U.S.?
It's hard to predict what the fiscal consequences are, but one example to consider is COVID. When you control COVID transmission in the United States though vaccination, what happens is that people do not end up accessing hospital care because they don't become severely sick. The more hospitalizations you have, the higher the cost to the health care system.
Not only is the cost higher, but there can be surges in activity that lead to the overwhelming of the health care system that makes it impossible to be seen for other things at the same time. Getting treatment for a heart attack or getting treatment for a broken bone will be impacted if you have large, sustained numbers of severe cases of any disease.
We saw this with COVID and we are likely to see this with other vaccine-preventable diseases as the numbers tick up.
What else should Americans know about vaccine safety in the United States?
I think people have forgotten how bad vaccine-preventable diseases can be: how bad polio was in the 1950s, how bad measles was, how bad pertussis can be. Now we’re starting to see those cases. We can see [that most of] the cases are people who are more vulnerable. We can see them [cases] in older adults and in people with cancer.
As we see the resurgence of all these vaccine-preventable diseases, it's important to remember that vaccines are safe. They're safe in the way that they're given. They're safe in the way they're designed. We've spent a lot of time making sure that they're safe. Not only have we made sure that they were safe before we started giving them, but we continue to assess the evidence and make sure that they are safe. If ever there were a situation where we thought the vaccines were not safe, then certainly we would take action and make that known.
What are the societal costs of having to go back and contain these once-contained diseases?
Rather than focusing on containment of measles and stopping the next outbreak of measles, we could be working on developing novel vaccines for new diseases, focusing on responding to the next potential pandemic. There are other things that we should be spending our mental energy on right now rather than containing the diseases for which there is a vaccine that is safe and highly effective.
How is research at the University of Washington supporting the safety and efficacy of vaccines and ultimately impacting our public health and quality of life?
There's a lot of research that's happening at the University of Washington on vaccines. Some of the specific examples include designing new vaccines, such as at the UW Medicine Institute for Protein Design, where they're working on making the next generation of vaccines, all the way over to the work that's being done at Seattle Children's and the School of Public Health on vaccine hesitancy and how to talk to parents about vaccines. All of that is being impacted right now by what's happening with the federal research landscape. There’s also a lot of vaccine trials that are happening, both for use of current vaccines as well as newer vaccines that have newer platforms to be able to deliver the vaccines in different ways.
Is there anything else you'd like to talk about in terms of vaccines?
One of the things that we've been focusing on is what is the best next step in terms of science-based, vaccine recommendations. Now we are in a situation where potentially the vaccine decisions that are being made nationally may not be in line with the known scientific evidence. Washington state, several other states, as well as many professional organizations in the United States, including the American Academy of Pediatrics, are working hard to look at the evidence and be able to make science-based recommendations for vaccines for use in the U.S.
What should people know about vaccine hesitancy in the U.S.?
There has been a rising anti-vaccine movement in the United States. The first thing to know, which is really important, is that most people are getting their vaccines on time and most people are getting all of the vaccines that are recommended by their doctor for themselves and their children. The choice that is in line with the majority is to get all of your vaccines.
Part of the reason why there has been an anti-vaccine movement, I think, is because of a rising distrust in science and a sense that the public is not being told what is happening. One of the ways that we try to address that is by having conversations as doctors with our patients and addressing their concerns. Also, we work to educate the public on the science and evidence supporting vaccine safety. There is an entire set of people and sets of data that we're studying, and who are devoted to studying all of this, and making sure that anything that comes up is addressed. We make policy decisions based on the best, newest, most available scientific data.