Experts urge testing of ‘as many vaccines as we can’

NEW YORK — Each of the Ebola vaccines being lined up for testing carries potential downsides, researchers say, ranging from efficacy that faded in less than a year to the chance it will give healthy people flu-like symptoms.

Human trials, just starting on some vaccines, could also unveil unknown side effects, an unwelcome possibility for shots designed to be taken by people who may never be infected with Ebola. That is why it is imperative to cast a wide net in seeking a solution, said Mr Matthias Schnell, a microbiologist at the Thomas Jefferson University in Philadelphia.

“We really should test as many vaccines as we can,” said Mr Schnell, who is working on a vaccine that targets Ebola and rabies.

“We need way more clinical data for each vaccine before we go ahead with mass vaccination.”

Safety testing has already begun on vaccines from GlaxoSmithKline Plc (GSK), which is working with the US National Institutes of Health and NewLink Genetics Corp (NLNK), which is testing a product developed by government researchers in Canada. The next step, efficacy trials in humans, could start next year for Glaxo’s product in affected regions in Africa.

Meanwhile, clinical trials could begin later next year for as many as three other vaccines.

While the vaccines have shown some levels of effectiveness in animals, that is no guarantee they will work as well when they are tested in humans, said Mr Thomas Geisbert, a virologist at the University of Texas Medical Branch in Galveston, Texas.

“That is why it is good to have an arsenal,” he said. “So that if one does not work, you will have plenty of alternatives.”

Vaccines work by stimulating the body to generate antibodies with the ability to remember the virus. That allows them to recognise Ebola once an infection takes place and mount a rapid counterattack.

They differ from ZMapp and other experimental medicines given to Ebola patients primarily because the vaccines are designed for healthy people as a way to keep them from becoming infected.

The Glaxo and NewLink vaccines have both been shown to be effective in monkeys, so there is every reason to think they will be effective, said Mr Kartik Chandran, a microbiologist at the Albert Einstein College of Medicine in New York.

“But you cannot assume the same thing will hold true in humans. There have been nasty surprises before.”

The vaccines from Glaxo and NewLink are based on modified viruses that are changed so they express an Ebola protein that is strong enough to stimulate an immune response, but does not carry the part of the Ebola virus that makes people sick.

Glaxo’s vaccine is based on a chimpanzee cold virus, while the NewLink vaccine is based on vesicular stomatitis virus, which is found in cows.

For London-based Glaxo’s vaccine, there are unanswered questions about whether it will be able to protect against Ebola for an extended length of time, Mr Schnell said.

A study in monkeys, published last month in the journal Nature Medicine, showed efficacy of the single-dose version of the vaccine waning over several months. While one dose of the vaccine protected all of the monkeys given the vaccine from a lethal dose of Ebola after five weeks, it protects about only half of the animals after 10 months.

Giving the monkeys a booster shot of a different vaccine construct provided longer-lasting protection, but Glaxo is not using that version in its initial studies in humans. BLOOMBERG