Some two million foreigners and possibly as many Saudis are expected to descend on Mecca and Medina for the hajj, which takes place in the middle of the northern hemisphere's winter flu season in November.
The hajj and the umrah, the lesser pilgrimage which can be done at any time of the year but peaks in the holy month of Ramadan, are both conducive to the spread of the virus, as hundreds of thousands of worshippers from all over the world gather in close proximity in Saudi Arabia's holy sites.
In July, Arab health ministers recommended banning those over 65 and under 12 from travelling. They also urged pregnant women and those suffering from chronic illnesses to refrain from making the trip, a recommendation that was supported by the majority of Arab governments.
Saudi Arabia played down concerns, saying that only 26 cases of swine flu were reported in the kingdom during Ramadan, which this year ended on September 20, and none of them were fatal, although several million Saudis and foreigners flocked to Islam's two holiest cities.
In total, 29 people have died of the virus in the kingdom since the disease was first detected.
Saudi authorities are calling on hajj pilgrims to get normal flu shots and, if vaccines are available in time, specific swine flu inoculations as well.
Egypt, the Arab world's most populous country with 80 million inhabitants, recently reinforced its swine flu testing measures at airports as thousands headed home after the Ramadan umrah.
The number of Egyptians expected to perform hajj will drop 30 to 40 percent this year due to the travel restrictions, an official told AFP, and stricter measures may yet be introduced.
"A decision could be taken at any time to cancel hajj this year," Egyptian Health Minister Hatem al-Gabali said recently.
Egypt has taken several measures to curb swine flu including shutting down schools and universities until October 3 in order to contain the risk of contamination.
Over 900 cases of swine flu have been reported in the country, with two swine flu related deaths reported so far.
Tunisia, which had already suspended the Umrah, has urged its worshippers to put off hajj for a year.
In Morocco, there has been no talk of calling off the hajj, but the ministry of health said only those vaccinated would be able to travel to Saudi Arabia.
In the Gulf countries and in Yemen, authorities have urged worshippers to get vaccine shots as soon as they are made available.
Iraq in August imposed restrictions on who may go on the hajj after banning everyone from carrying out the minor Umrah pilgrimage during Ramadan.
Neighbouring Iran also banned pilgrims from travelling to Mecca in Saudi Arabia during Ramadan.
In Jordan, authorities issued a religious edict urging Muslims to avoid kissing each other.
The A(H1N1) virus has killed 3,917 in 191 countries and territories since it first appeared in April, according to the WHO.