Don't Pin Hopes for Stopping SARS on Creating Vaccine

By Dr. Joan B. Rose
May 25, 2003

Recently, more than 48,000 people showed up in Toronto to watch the Blue Jays play the Rangers. While ticket sales no doubt were helped by a $1 per seat promotion, the large crowd also was a result of the World Health Organization's decision to lift its travel advisory to the city.

The good news in Canada was that SARS -- severe acute respiratory syndrome -- appeared to be under control, until the discovery Friday of a possible new cases.

The news is not as good throughout the world. By latest count, more than 7,700 SARS cases have been reported around the globe, with more than 620 deaths. More than 25 nations are now battling the SARS epidemic. And health officials maintain that SARS could easily recur even in regions that appear under control.

In mid-April, researchers concluded that a new pathogen, a member of the coronavirus family never before seen in humans, is the cause of SARS. Other pathogens within the coronavirus were first isolated and described in the 1960s from respiratory secretions in adults with the "common cold."

With that knowledge, global health officials are now placing considerable attention toward developing a SARS vaccine. While these efforts should continue, it is important to remember that similar endeavors to create a vaccine for the common cold have not succeeded. So more immediate returns may be obtained from studying exposure routes and methods to reduce the risk of exposure. This type of information can lead to approaches for controlling the virus that can be implemented easily and rapidly.

What can we learn about this emerging virus from the research gained from studying other coronavirus pathogens? We know that most viruses have a low infectious dose, which means that only a few are needed to begin an infection. Coronavirus is thought to spread primarily through person-to-person transmission. Coronaviruses, including the SARS virus, have been found in fecal material. These viruses can live on surfaces (according to one study, for as long as six days), and transmission from contaminated surfaces to humans is possible.

Direct exposure to the virus from a sneeze or contaminated hands from one person to another seems to pose the greatest risk of transmission. Lesser risks would be associated with contact with the virus through surfaces or materials. However, the level of the risk reduction and the potential for transmission has not been quantified.

We also know that airborne human coronavirus is more likely to survive in colder temperatures. Because of this, health officials are bracing for an increase in SARS cases in the fall. And research has shown that certain chemical disinfectants (but not all) can be effective in killing coronavirus on various surfaces.

A simple Google Internet search will turn up numerous products that purportedly protect against SARS -- such as masks, air filters, hand gels, disinfectants, diet supplements and colloids. The public should not rush off to purchase these products. Health experts simply do not know enough about exposure transmissions and how effective these products are in protecting against the virus.

But there are simple preventive measures the public should employ. First and foremost, we should frequently wash our hands with soap and water -- the foundation of good hygiene. In addition, proper disinfection of surfaces -- particularly in health care settings, but also in the home -- can help ward off most germs and viruses. In fact, in an encouraging step announced last weekend, the World Health Organization concluded that SARS loses its ability to infect people after exposure to different commonly used disinfectants, such as chlorine bleach.

Though hand washing and disinfection are hallmarks of public heath protection, it is important to remember that these measures have not been fully tested against the SARS virus. Therefore, as the global health community races to develop a SARS vaccine, it must equally invest in understanding exposure. Experts believe a vaccine can be developed in one to three years, an optimistic timetable. But without more knowledge about exposure routes, one to three years will be too long.