Timeline of the 2009 H1N1 Flu Outbreak: The Beginning

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January 4-March 11, 2009

As part of its routine seasonal flu monitoring activities, Mexican health authorities collect 51 specimens positive for influenza A. They are later tested for swine flu at the CDC and all come back negative.

March 18

Cases of influenza-like illness (ILI) begin to be noted by health authorities in Mexico.

April 12

An outbreak of ILI is reported in the state of Veracruz, Mexico, east of Mexico City.

April 17

A case of atypical pneumonia in the state of Oaxaca, Mexico, in the south of the country, is reported. Mexican health authorities ask hospitals to report all cases of severe respiratory illness and collect laboratory specimens from them.

April 23

Following a steady rise, a total of 854 cases of pneumonia, presumably resulting from ILI, have been reported in Mexico City with 59 deaths.

Meanwhile, in San Luis Potosí, Mexico, north of Mexico City, 24 cases of ILI with 3 deaths have be reported, and in Mexicali, just south of California, four cases of ILI with no deaths have been reported.

These flu-like illnesses affect more healthy young adults and fewer of the very young and elderly than typical flu does. Several of them are laboratory confirmed as swine-origin influenza A (H1N1) virus of the same genetic strain as that detected in two children in California.

April 25

The Director-General of the WHO, Dr. Margaret Chan, declares a Public Health Emergency of International Concern.

April 26

CDC reports 20 laboratory confirmed human cases of swine influenza A/H1N1 from across the entire continental United States. All are classified as mild ILI with no deaths reported. Preliminary testing shows all have the same genetic makeup, and the virus is described as a new subtype of influenza A H1N1.

Mexican government reports 18 laboratory confirmed cases of swine influenza A/H1N1, with possible cases reported in 19 of the country’s 32 states.

April 27

CDC lab confirmed human cases total 40 (0 deaths). Mexico lab confirmed human cases total 26 (7 deaths). Canada reports 6 cases (0 deaths). Spain reports 1 case (0 deaths).

April 28

A total of 7 countries report lab-confirmed cases of swine influenza A/H1N1 infection. CDC reports 64 confirmed cases (0 deaths) and Mexico reports 26 (7 deaths). Other countries have reported a handful of confirmed cases with no deaths: Canada, Spain, New Zealand, the United Kingdom, and Israel.

April 29

A total 148 laboratory-confirmed cases are reported in 9 countries; most of these are in the U.S. (91) and Mexico (26). There is only one new death, in the United States. New countries reporting infections are Austria and Germany.

April 30

A total of 11 countries now report lab-confirmed cases. The total for the United States is 109. New countries reporting infections are the Netherlands and Switzerland.

Total H1N1 cases in Mexico: 1,918 suspected (i.e. patients with flu-like illness), 286 of which are probable (i.e. test positive for influenza A) and 97 of which are confirmed (i.e. laboratory genetic testing confirms swine influenza A/H1N1). Total deaths in Mexico: 84 suspected and 7 confirmed.

Mexico’s Health Secretary José Angel Córdova expresses “optimism” based on the stabilization of the number of new confirmed cases in Mexico, noting that the data from the next few days will be “critical.”

May 1

A total of 13 countries now report lab-confirmed cases totaling 365. Most of these are in Mexico (156), the United States (141), and Canada (34). New countries reporting infections are China (Hong Kong) and Denmark.

Two more lab-confirmed deaths are reported in Mexico for a total of nine.

May 2

A total of 16 countries now report a total of 658 lab-confirmed cases. The total in Mexico is 397, with health officials there noting that the apparent sudden increase from the previous day is indicative of test results coming back, not of a sudden jump in the number of illnesses. Mexico now reports 16 lab-confirmed H1N1 swine flu deaths.

The United States total is now 160 cases and the Canada total is 51 cases. All other countries report 15 or fewer cases each. New countries reporting lab-confirmed cases are Costa Rica, France, and South Korea.


First pilot lots of a vaccine may become available for testing.

November-January 2010

If it has been ordered by health officials, enough vaccine may have been produced for large-scale vaccination in the U.S.