TOKYO -- U.S. drugmaker Pfizer lifted spirits worldwide this week with word that its vaccine candidate was found to be "more than 90% effective in preventing COVID-19."
Scientists think it could lead to a victory against the coronavirus, but warn against premature optimism and want more information before drawing conclusions. Here are five things to know.
What does it mean?
Most vaccines are meant to increase the body's immune response against a virus and thereby ease symptoms such as fever, rather than preventing the actual infection from happening.
Details on the Pfizer candidate remain scarce. Experts say the public should not presume that a vaccine will eliminate the risk of catching the virus at all.
What technology went into the vaccine?
The vaccine candidate developed by Pfizer and German company BioNTech relies on genetic engineering based on messenger RNA. Genetic instructions are injected into human cells so they will assemble something that looks like the coronavirus and allow the body's immune system to prepare for its invasion.
Traditional vaccines inject a weakened form of an actual virus into people. Gene-based vaccines are a fast-developing field, but they have yet to be used for humans.
How long will the effects last?
This remains to be seen.
The way vaccines work is by inducing a response from the body's immune system. But a vaccine's efficacy declines over time. Influenza vaccines work for only four months or so, but that is enough because the flu season is usually short -- three months in winter -- said Ko Ichihashi, professor at Jichi Medical University in Japan.
The coronavirus is more of a year-round problem. Outbreaks constantly happen somewhere in the world, meaning that the virus could be brought into a region at any time. If the effects of the vaccine are short-lived, individuals might need to be vaccinated three or four times a year.
Does it work for everyone?
The effects of a virus can differ among populations, and viruses also mutate constantly. Coronavirus strains that are spreading in Europe are known to be different from those that have broken out in Asia.
Pfizer says its trial involves 43,538 people in the U.S. and other countries, which suggests that the vaccine candidate may be broadly effective. Ichihashi says the current coronavirus strains probably do not differ enough to require different vaccines.
Will there be enough supply?
Messenger RNA is a large molecule that is difficult to manufacture and store. A production line can stop because of even a tiny amount of contamination. Smooth production is by no means guaranteed.
Japan, the U.S. and the U.K. have agreements to receive tens of millions of vaccine doses from Pfizer. The U.S. company is also in talks with Hong Kong and the Philippines to supply the vaccine candidate, according to Airfinity, a science information and analytics company.
But countries have lined up other suppliers so that any problem with Pfizer or another developer would not mean a complete loss of vaccine availability.
Pfizer alone lacks the capacity to meet global vaccine needs. Other drugmakers will continue their own vaccine development and give countries more choices.
Other developers now face the high bar set by Pfizer, far exceeding the 50% efficacy rate demanded by the U.S. Food and Drug Administration, said Sunao Manabe, president and CEO of Daiichi Sankyo, a Japanese drugmaker and developer of a similar coronavirus vaccine candidate. Daiichi Sankyo aims to start a clinical trial on its own messenger RNA candidate in March.
"We'd like to achieve an efficacy rate as high as Pfizer's," Manabe said in an interview.
China and Russia are likely to continue their domestic vaccine programs. China has promised vaccines to neighboring countries, a campaign that is expected to increase Chinese influence in Asia.