Ravi Jhaveri, MD, reviews the different types of influenza vaccines for pediatric populations, highlighting the differences between egg-based and cell-based flu vaccines.
Ravi Jhaveri, MD: So when we think about the recommendations for [pediatric patients,] flu vaccine is recommended for all children 6 months and older, and it doesn’t matter about health condition. We are lucky that we [now] have several options for children; when I started my career, we had 1 option. Now we have several. But the idea is that there is a version, some version, that is approved for all children 6 months and above. We have the injectable versions, which are the egg-based versions, as well as the cell culture–based version. We also have the intranasal live attenuated vaccine as well for kids [aged] 2 and older. So as we think about different conditions, we can offer some choice, sometimes that is convenience and whatever [a] pharmacy or [a] doctor’s office may have. Occasionally we also perhaps are able to accommodate if patients have strong preferences either for trying to avoid needles, or perhaps for avoiding egg or egg products if there’s allergy, or also, some discussion about perhaps increased effectiveness in some of the cell culture versions because we avoid some of the egg-induced mutations that might compromise the activity of the vaccine. So as we think about the differences between vaccines that are produced in chicken eggs vs vaccines that are produced in cell culture, we really think about the preparation, so I’ll take a brief moment to just talk about how the flu vaccines are produced. The first thing that has to happen, because these vaccines are made from the proteins that the virus makes, is we have to generate large stocks of virus and then ultimately collect those proteins. So for years and years and years, we would do this in unfertilized chicken eggs. And the flu virus grows very well in chicken eggs.
We would use many millions of eggs to grow many millions upon millions upon millions of new virions, and then collect that virus and purify the contents, the hemagglutinin and neuraminidase, and then put it into our seasonal vaccines. Over time, what we’ve realized is that there are challenges with eggs. One obvious [challenge] is that supply can often vary based on the availability of eggs. And so we wanted to have a more stable supply. And so the adaptation to using cultured cells in a laboratory where you essentially have an endless supply of immortalized cells. The flu virus can grow very well in those eggs. And then the process of purification and packaging into vaccine is essentially the same. What we have appreciated over the last several years is actually that growth process in eggs, in order for the flu virus to grow efficiently, it has to mutate. And those mutations ultimately cause it to grow very well in eggs. But now we’ve come to realize through good science that those mutations in eggs actually may ultimately compromise or lower the effectiveness in a human and their immune response. And it’s because the circulating flu strains that we are exposed to in any given season don’t have those mutations. And those mutations often come in the key proteins we’re talking about, the hemagglutinin, for instance. So there’s been an effort and a reevaluation about the difference in terms of effectiveness with cell culture–based vaccines and egg-based vaccines.
I want to emphasize that I still want to go back to the idea that any vaccine is better than no vaccine. And we want to make sure that all people can get a vaccine. But if you’re offered the choice, there are some real theoretical benefits and real benefits to getting a cell culture–based vaccine. So, as we think about egg adaptations, there’s 1 additional point that warrants mention, which is [that] the process for selecting flu strains actually involves an international collaboration with the global agencies of public health, the WHO [World Health Organization], the CDC [Centers for Disease Control and Prevention], the European agencies, the Chinese agencies, [and] other Asian groups as well. And there’s a decision about which flu strains are thought to be circulating, which ones circulated previously in the Southern hemisphere, which ones are predicted to circulate in the Northern hemisphere. And so, it’s part art and part science in terms of predicting those strains. But once those strains are decided upon and agreed upon, the strains are shared with all the manufacturers of flu vaccine. And for years and years, those strains were maintained in eggs. So there was a concern or a likelihood that, in fact, the initial process and strains had the mutations already. And so one of the updates over the last several years is actually to remove eggs from that strain, initial strain selection and propagation process. So when a manufacturer has the initial strains to generate their stocks, those are not producing eggs any longer. And this reflects the concern about egg mutations.
Transcript is AI-generated and edited for clarity and readability.