South Korea’s health authorities said Tuesday it is “encouraging” that US pharmaceutical firm Pfizer has made a breakthrough in developing a vaccine against the coronavirus, but warned against “hasty” expectations.

Pfizer announced Monday that its vaccine candidate developed with BioNTech was found to be more than 90 percent effective in preventing COVID-19, raising hopes for bringing forward an end to the global fight against the pandemic.

“As the virus situation abroad is too serious, there seem to be heightened expectations (about the results),” Sohn Young-rae, a senior health official, told reporters, adding it is just an interim result of phase 3 clinical testing. “The effectiveness of the vaccine remains to be seen and it is hasty to expect it to be effective.”

Korea reported 100 new coronavirus cases -- 71 locally transmitted and 29 imported from overseas -- in the 24 hours ending Monday at midnight, according to the Korea Disease Control and Prevention Agency.

The daily tally saw a triple-digit gain for the third consecutive day Tuesday, leading authorities to consider moving up the level of social distancing by a notch in the country’s five-tier social distancing scheme.

Currently, the lowest Level 1 social distancing rules are in place, with most antivirus restrictions lifted in most parts of the country. Exceptions are Asan and Cheonan in South Chungcheong Province, which are grappling with recent spikes in coronavirus cases.

“The country may revise up the social distancing scheme to Level 1.5 after two or three weeks, should the current trend continue,” Sohn said.

Sporadic clusters of infections emerged in connection with a family gathering and a private cram school. Cases linked to workplaces, nursing homes and private gatherings continue to rise.

Of Tuesday’s locally transmitted cases, the majority were in Greater Seoul -- 32 in Seoul and 18 in Gyeonggi Province, which surrounds the capital. Four cases each were reported in Gwangju and South Chungcheong Province, with three each in Incheon and Gangwon Province.

The transmission route for 12.7 percent of cases reported for the past two weeks remained unknown as of Tuesday, according to the KDCA.

Korea reported 29 imported cases. Among them, 21 were identified while the individuals were under mandatory self-quarantine in Korea, with the other eight detected during the screening process at the border. Eighteen cases were from the Americas, six came from Europe and five were from elsewhere in Asia. Eighteen of those cases involved foreign nationals.

The number of COVID-19 patients in serious or critical condition here was 54.

Five more people died from the virus, bringing the death toll to 485. The overall fatality rate is now 1.75 percent.

So far, of the 27,653 people confirmed to have contracted the new coronavirus here, 25,160 have been released from quarantine upon making a full recovery, up 131 from a day earlier. Some 2,008 people are receiving medical treatment under quarantine.

The country carried out 14,761 tests in the past day. A total of 27,855 people were awaiting results.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)