TOKYO -- As new variants of the coronavirus gain a foothold around the world, countries have ramped up efforts to track and combat them, as well as keep tabs on other potentially dangerous mutations as the pandemic wears on.
A variant first identified in the U.K. late last year had been found in 32 countries as of Dec. 30, according to the World Health Organization. Media reports put the total at 33, including the U.S., France and Germany. Another mutated virus discovered in South Africa has been reported in five countries, the WHO says.
Genome analysis has become a crucial tool for tracking these variants. In Japan, where both have been found, the National Institute of Infectious Diseases has been analyzing samples from domestic cases since the early days of the outbreak.
The institute had sequenced roughly 14,700 -- about 6% of the country's confirmed cases -- as of Dec. 31, finding virus variants in three people with a history of recent travel. Later analysis has shown no sign of local transmission.
The NIID plans to conduct a broad survey of cases from November and December to ensure that the more infectious variant has not made headway here. Director-General Takaji Wakita said Tuesday that the organization has developed a rapid detection method for the coronavirus variants, to enable regional public health offices around the country to help with this effort.
The steady flow of information from the U.K. about the variant found there owes to an aggressive genome analysis campaign. Roughly 170,000 virus samples, equivalent to 6% of all British cases, had been sequenced there as of Wednesday, according to sources including the COVID-19 Genomics UK Consortium, or COG-UK.
Japan is roughly on par with this effort, while the U.S., with its much higher number of cases, has fallen short. The U.S. had analyzed around 51,000 samples as of late December, according to the Centers for Disease Control and Prevention, covering just 0.3% of infections.
People with the U.K. variant with no history of overseas travel have been found in countries including Switzerland, Denmark and the U.S. Many countries have detected cases during airport quarantine screening, without seeing broader transmission. But the limited number of nations with genome analysis capabilities makes it impossible to get an accurate picture of its spread.
While the U.K. variant is not known to cause more severe illness, it is believed to be more contagious.
After London locked down for a second time in November, transmission of the standard virus declined, yet the mutated version spread rapidly. It accounted for 62% of all new cases in London by the week of Dec. 9, up from just 28% during the week of Nov. 18, and shows no signs of slowing. The country's total daily infections topped 60,000 for the first time on Tuesday.
A model developed by the London School of Hygiene & Tropical Medicine estimated that the variant is 56% more transmissible than the standard strain. Imperial College London found that its reproduction number -- the average number of new infections caused by each carrier -- is 0.4 to 0.7 higher.
Some experts have voiced concern about whether mutations in the virus, particularly in the South African variant, could make existing vaccines and treatments less effective.
The Pfizer-BioNTech and Moderna mRNA vaccines can be easily adapted to new variants of the virus if necessary, by rewriting the mRNA code to mimic the mutation. BioNTech CEO Ugur Sahin has said that a new version of the vaccine could enter mass production in just six weeks.
In response to the surge in infections in the U.K., the government there has issued guidance that calls for delaying the second dose of the AstraZeneca-Oxford vaccine, to get the first dose to as many people as possible. For the Pfizer-BioNTech vaccine, shots are to be administered 12 weeks apart rather than the recommended three.
The policy has been criticized by medical experts, as it is unclear whether the vaccines will still be safe and effective when administered on a different schedule than that used during clinical trials.
The U.S. Food and Drug Administration issued a statement Monday stressing "the importance of receiving COVID-19 vaccines according to how they've been authorized by the FDA in order to safely receive the level of protection observed in the large randomized trials supporting their effectiveness."