Grave concerns remain over the A/H1N1 flu outbreak even though studies suggest that the virus is less lethal as previously anticipated while Mexico is set to allow most businesses to reopen on Wednesday.

Mexican Health Minister Jose Angel Cordova said on Monday that four new deaths from the A/H1N1 flu have been confirmed, bringing the death toll to 26, with 727 total confirmed infections.

However, Cordova said that the disease had a comparatively low R0 number, which means it is not much more contagious than normal seasonal flu.

"The studies which we have, based on the tests which are being confirmed and ruled out, have shown epidemiologists that the trend is lower, towards a decline in cases," said Cordova.

Mexican President Felipe Calderon announced on Monday that Mexico, the epicenter of the outbreak, will return to "normalcy" on Wednesday, ending a five-day nationwide shutdown of the country's most businesses.

Universities and high schools will reopen on Thursday, and younger schoolchildren should report back to school early next week, he said.

However, officials and experts have called for continued vigilance as prospect of the disease outbreak remains uncertain.

Feiji Fukuda, the WHO's director for health security and environment, stressed that it is "critical" for governments to maintain and strengthen their alert and surveillance, given the continued spread and the highly unpredictable behavior of the virus.

He expressed particular concern that the new virus might spread in the southern hemisphere, where the winter season is coming and flu viruses tend to be more active.

Still, the WHO left its pandemic alert level unchanged at Phase5, citing the fact that there is still no sustained human-to-human infections of the new virus in regions out of North America.

The WHO said it had no clear plan to raise the alert level to Phase 6, the highest level which means a full pandemic is occurring.

Most of the infections in Europe and Asia were "travel-related cases," which means the virus has not taken root there, said Fukuda.

The UN Food and Agriculture Organization ( FAO) said on Monday that national authorities and farmers should carefully monitor pigs and investigate any possible occurrences of influenza-like symptoms in domestic animals.

"The human-to-animal transmission that occurred in Canada does not come as a surprise as influenza viruses are capable of transmitting from humans to animals," FAO's Chief Veterinary Officer Joseph Domenech said.

Surveillance for porcine respiratory disease should be intensified and all cases of porcine respiratory syndrome are recommended to be immediately reported to veterinary authorities, FAO said.

The UN body also suggested governments inform any occurrence of outbreaks of the new A/H1N1 Influenza virus in pigs to international agencies concerned.

Strict biosecurity measures including restriction of movements of pigs, goods and people should be applied on all farms or holdings with swine showing signs of clinical respiratory illness until diagnosis of the illness has been made, the FAO said.

Meanwhile, the UN General Assembly opened a special session on Monday to discuss the challenge of the A/H1N1 flu, with UN Secretary General Ban Ki-moon urging " global solidarity" and "multilateralism" to combat the disease.

"We need to respond with a vigorous new multilateralism. We need to help those countries, especially in the developing world, which may find it hard to respond to this threat. That is only way to secure global public health," Ban told the special session, the first on the issue since the outbreak in late April.

The Cairo-based Arab League (AL) said Monday that the executive office of Arab health ministers' council is to hold a meeting in Saudi Arabia on Tuesday to discuss means of confronting the plague, in a fresh bid to fend off the fatal A/H1N1 flu virus via collective measures among Arab nations.

Well-informed sources from the pan-Arab body told Xinhua that Saudi Health Minister Abdullah al-Rabia, head of the office of Arab health ministers' council, invited the Arab health ministers to an emergency meeting for consultation about fighting the new virus.

At the same time, AL said that the Arab health ministers will discuss available human and technical capabilities in dealing with the disease.

A total of 21 countries have officially reported 1,085 lab-confirmed human infection cases of the A/H1N1 flu virus to the World Health Organization (WHO) as of 18:00 GMT on Monday, the UN agency said in a latest update.

The largest numbers of cases were still reported from North American countries, notably Mexico and the United States. The United States has 286 confirmed cases, including one death.

Other countries and regions that have reported laboratory-confirmed cases with no deaths are Canada (101), Austria (1), Hong Kong, China (1), Costa Rica (1), Colombia (1), Denmark (1), El Salvador (2), France (4), Germany (8), Ireland (1),Israel (4), Italy (2), the Netherlands (1), New Zealand (6), Portugal (1), the Republic of Korea (1), Spain (54), Switzerland (1) and Britain (18).

The Italian health ministry later Monday reported two new confirmed infections, bringing the total number of confirmed cases to four.

The two new cases are a 16-year-old girl and an 11-year-old boy, both of whom are being treated in hospitals in Rome after returning from Mexico.

Brazil's Health Ministry announced on Monday that 25 people were suspected of being infected with the A/H1N1 flu in the country. The country has so far no reports of confirmed infections.