MANILA, Philippines -- (UPDATE) The Department of Health (DoH) confirmed on Sunday the country's second case of the potentially deadly Influenza A(H1N1) virus.

Officials warned that while the victim had apparently recovered as of Sunday, Filipinos should not let their guard down because the virus could mutate into a "more virulent" type.

The second case is a 50-year-old Filipino woman from Chicago who flew into the Philippines on May 20.

?She appears to have already recovered,? Health Secretary Francisco Duque told reporters shortly after arriving from the 62nd World Health Assembly in Geneva.

He said the H1N1-positive woman no longer had any symptom of the flu as of Sunday.

?It?s consistent with global findings that this virus is mild in form and perhaps the information that we gathered (is that) ordinary seasonal influenza has a much higher case fatality rate of about 10 percent,? he added.

Out of the more than 12,000 cases of H1N1 flu virus infection in 43 countries reported to the World Health Organization, there have been 86 deaths. This translates to a global mortality rate of just 0.7 percent.

Duque, nonetheless, called for sustained watchfulness and discouraged complacency because the H1N1 flu virus remained unpredictable.

Its evolution into a more lethal strain has not been ruled out, said Duque.

?We have past experiences with the 1918 pandemic, the 1957 as well as the 1968 pandemics and you would see that in the initial phase, there could be some parallels in terms of how the virus can possibly evolve to become more virulent at some point in time,? Duque said.

?But of course, that is pure conjecture and speculation (at this point),? he added.

The 1918 influenza pandemic, according to the United States Center for Disease Control website, killed 50 million worldwide.

?It is extremely crucial that we continually monitor the risk to which people are exposed without unduly causing panic, on the one hand,? Duque said.

?On the other hand, it is important that we do not underestimate the threat and the risk of this novel virus that it will create complacency. That is not the objective of our effort,? he added.

Health officials said the second index case arrived in the country on May 20. They said she sought treatment on May 21 after exhibiting mild symptoms of cough and fever.

?When she was attended to, she was already on her way to recovery,? Duque said, citing the findings of the Research Institute for Tropical Medicine (RITM).

The RITM said the 50-year-old index case was given oseltamivir treatment immediately.

?When we examined the specimens, the viral load was already very low although it?s still positive so It?s possible that in a few days, it will already become negative,? said Doctor Remigio Olmeda, RITM director.

Doctor Mavic Vasquez of the Bureau of Quarantine said the agency has identified the 25 passengers that could be considered as close contacts of the second index case.

?It?s easy to reach them because their addresses and (contact) numbers are available,? Vasquez said.

Health Undersecretary Mario Villaverde said the regional epidemiology centers have been informed because a number of the possible contacts went to the provinces.

?We have already contacted the airline. And we were able to recover the flight manifest?. We have informed regional epidemiologists especially some of the co-passengers have gone to ? their hometowns,? Villaverde said.

Health officials place the number of contacts of the second index case at ?less than ten.? Villaverde said all contacts were told to observe themselves for symptoms and to report immediately to authorities once they develop symptoms of flu.

Doctor Eric Tayag, director of the DoH National Epidemiology Center, said the protocol for confirmed cases required those who had lost their symptoms to take another polymerase chain reaction or PCR test for the H1N1 flu virus.

?Cases are tested again before they are discharged. And negative means they cannot infect other people. And that?s complete recovery,? Tayag told reporters.

The first confirmed case?a 10-year old girl who traveled to the US with her parents?was almost fully recovered as of Sunday, Duque said.

?She is completing her anti-viral medications and will be discharged as soon as the repeat PCR for influenza A H1N1 is negative,? the secretary said.

?Contact tracing has also been done and all household contacts were given anti-viral prophylaxis. They are complying with the DoH advice to stay at home for 10 days while monitoring for the development of influenza-like symptoms,? Duque said.

On the Taiwanese who visited the country and then was found to be A H1N1-positive in her country, Duque said ?the DoH is continually investigating the case.?

?We have already coordinated with Taiwan Center for Disease Control who reported yesterday (Saturday) that the patient has already fully recovered. At present, her daughter only has mild respiratory symptoms and does not have fever anymore,? Duque said.

?Based on the information we have, the Taiwanese woman fell ill after visiting the Philippines for a short vacation. She did not attend any social gathering in the country, which could have exposed her to the virus while here in the Philippines,? he added.

Duque?s report on the Taiwanese case ran counter to the initial report that the Taiwanese attended a convention in Boracay. The health secretary said that apart from the two confirmed cases in the country, the DoH has been monitoring 10 new cases under observation.

?Of the new cases under observation, nine still have pending laboratory results for influenza A H1N1 together with six other previous cases,? Duque said.

?All other cases tested negative for influenza A H1N1,? he added.