With flu season fast approaching, the National Vaccine Program Office in the Department of Health and Human Services is increasing their efforts to develop a vaccine for H1N1 influenza, better known as swine flu, by October. But experts have expressed concerns that the viral strain needed to produce the vaccine isn’t replicating fast enough for mass production. There is also concern about potential side effects.

Since the outbreak of swine flu earlier this year, scientists have been working to create a vaccine in preparation for what experts believe may be the virus’ peak this fall. While the Centers for Disease Control and Prevention has stated that an annual influenza vaccine takes approximately six months to prepare, creating an H1N1 vaccine presents some challenges that might prolong the preparation. According to Prof. Colin Parrish, virology, “The problem with the swine flu vaccine for this year is that the virus that they are growing to put into the vaccine does not grow very well, and therefore [it] is proving to be harder to make enough of it to make an effective vaccine.”

Vaccine manufacturers say the seed strain, from which the vaccine will be cultured, isn’t multiplying as fast as it should. In response, scientists are proposing alternative ways to develop the vaccine as well as ways to speed up the process already in use. Officials suggest the inclusion of an immune-boosting agent known as an adjuvant to increase the number of available doses by reducing the amount of viral protein needed in each dose. According to Parrish, however, alternative production methods may not be developed in time for the CDC’s expected deadline. “There are ways to increase virus replication rates, but they would likely be difficult to optimize in time to be useful this season. So, mainly they just have to make more of the virus by growing extra,” he said in an e-mail.

Novavax, an American pharmaceutical company, began testing another approach during seasonal flu vaccine trials in May. In the traditional process, scientists crack the shell of a fertilized chicken egg and inject the influenza virus into the fluid surrounding the embryo, allowing the virus to multiply. Instead of adapting the virus strain, Novavax’s alternative uses novel virus like particles (VLPs), which contain the same surface proteins as the virus, allowing the body to build immunity. In other words, because this process does not use the live virus, it does not have to be inactivated before it is injected into the eggs. While the FDA remains on alert, VLP-based vaccines have yet to cause a bad reaction in any patients.

With production of the vaccine in full swing, officials are also worried about potential side effects. In 1976, more than 500 people who had been vaccinated against a slightly different strand of H1N1 developed the debilitating Guillain-Barre syndrome, a disease in which the body damages its own nerve cells (outside of the brain and spinal cord), resulting in muscle weakness and sometimes paralysis. While some researchers remain worried, others believe the threat is miniscule. According to Parrish, “There is no specific reason to assume any specific risk of [Guillain-Barre syndrome] for this new vaccine, versus the others. At a rate of one per million, it is not easy to test for those types of side effects.”

Similarly, thimerosal has been removed from most vaccines in response to concerns over a link between the mercury-based preservative and autism in children. “There is no link to autism — that is completely wrong and has been conclusively investigated,” Parrish stated. U.S. health officials have also denied the link and have said that there is no evidence that this ingredient causes autism. But pharmaceutical companies are not taking any risks. CSL Ltd, an Australian based company, became the first to start trials of a thimerosal-free H1N1 vaccine in August.

When the vaccine becomes available, the CDC recommends that particular “target” groups receive it first: pregnant women, people who live with or care for children under six, healthcare personnel, people between six months and twenty four years of age and people with chronic health disorders or weak immune systems. Parrish agrees: “I think the vaccine will be safe and effective ... The swine flu virus seems to be quite mild, so it may be most important for people in specific susceptibility groups to get it.”