Why Pfizer’s RSV vaccine success is a big deal, decades in the making

Pfizer offered a glimpse of hope Tuesday in the form of top-line, phase three clinical trial results, after a large and early seasonal surge ofRSV cases in children's hospitals.

In the first three months of an infant's life, the company's experimentalRSV vaccine was effective at preventing severeRSV-related lower respiratory tract illness. It was effective for 69 percent of the time.

The first-ever vaccine shown to help protect newborns against severeRSV-related respiratory illness immediately at birth is a Pfizer invention.

It is possible that a vaccine could be available in time for next year's season if the FDA approves the company's application by the end of the year.

There are reasons to be cautious with the announcement. Only top-line results have been released in a press release. The data needs to be reviewed more thoroughly. The vaccine did not meet the second of the trial's two primary goals, which was to reach the pre-determined statistical criteria for efficacy against non-severeRSV-related lower respiratory tract illness.

There is reason to be excited by Tuesday's news, which follows decades of struggle by researchers trying to fightRSV In the 1960s, a vaccine trial led to the death of two infants and the development of more severe disease, which was caused by an outbreak of the respiratory syncytial virus.

An oft-overlooked virus

Respiratory syncytial (sin-SISH-uhl) virus, orRSV, is a common, seasonal virus that poses a grave risk to infants and toddlers. Most people don't experience a serious respiratory illness when they are children. It can be life threatening for a small percentage of children. Over 100,000 children under the age of 5 are killed each year by the respiratory syncytial virus. Babies under 6 months old and children in lower income countries are more likely to die.

One of the leading causes of hospitalization for children under the age of 5 in the US is respiratory syncytial virus. The Centers for Disease Control and Prevention estimates that between 58,000 and 80,000 children are sent to the hospital and between 100 and 300 die from the disease.

Researchers have been trying to prevent and treat the disease for a long time. Progress was halted for years due to a dark cloud. Researchers began work on a vaccine against the disease in the 1960's. The vaccine's design used a standard treatment of the times, heat and a solution of formaldehyde, to inactivate the virus. All of the vaccine's antigenic components were frozen in place so immune cells could learn to target key components.

Catastrophic candidate

The vaccine was a huge failure. It failed to protect children from the disease in several trials, but it made them more vulnerable to the disease.

Researchers gave infants between the ages of 2 months and 7 months a three-dose regimen. Only one of the 40 unvaccinated infants in the control group needed to be hospitalized after catching the disease. Of 30 infants given the vaccine, 20 went on to catch the disease, but 16 had to be hospitalized. Two of the children died of infections after being exposed to the respiratory syncytial virus.

The vaccine caused "enhanced respiratory disease" in the children who were given it. Weak antibodies were created by the formalin-inactivatedRSV vaccine. The impotent response led to a build up of immune complexes that increased inflammation. The vaccine caused T cell responses that can cause inflammation in the lungs. Severe disease can be caused by all of this.