I am not sure I buy that because we had data from China, France, Italy, etc. about what to expect.
By Jan 3, the Chinese had warned us.
{...
3 January
The Chinese government formally notified the U.S. of the outbreak. At a White House briefing in 20 March, Health and Human Services Secretary Alex Azar said officials had been alerted to the initial reports of the virus by discussions between CDC director
Robert Redfield and Chinese CDC Director Gao on January 3. Mr. Azar also told his chief of staff to make sure that the National Security Council was aware that "this (the outbreak) is a very big deal"
[26][27][28] The BBC ran its first story on the outbreak.
[29]
Health authorities in Wuhan reported 44 cases, a big jump from the 27 reported on Tuesday. Eleven of the 44 were seriously ill, the Wuhan Municipal Health Commission said, although there had been no reported deaths to date. The health of the 121 close contacts of the cases was being monitored.
[30]
...}
{...
The virus was confirmed to have reached France on 24 January 2020, when the first
COVID-19 case in both Europe and France was identified in
Bordeaux. The first five confirmed cases were all individuals who had recently arrived from China.
[5][6] A Chinese tourist who was admitted to hospital in Paris on 28 January 2020, died on 14 February 2020, making it the first COVID-19 death in France as well as the first COVID-19 death outside Asia.
[7][8][9][10] A key event in the spread of the disease across
metropolitan France as well as its
overseas territories was the annual assembly of the
Christian Open Door Church between 17 and 24 February 2020 in
Mulhouse which was attended by about 2,500 people, at least half of whom are believed to have contracted the virus.
[11][12] On 4 May 2020, retroactive testing of samples in one French hospital showed that a patient was probably already infected with the virus on 27 December 2019, almost a month before the first officially confirmed case.
[13][14]
...}
{...
The virus was first confirmed to have spread to Italy on 31 January 2020, when two Chinese tourists in Rome tested positive for the virus.
[1] One week later an Italian man repatriated back to Italy from the city of
Wuhan, China, was hospitalised and confirmed as the third case in Italy.
[3] Clusters of cases were later detected in
Lombardy and
Veneto on 21 February,
[4] with the first deaths on 22 February.
[5] By the beginning of March, the virus had spread to all regions of Italy.
[6][7][8][9]
On 31 January, the Italian government suspended all flights to and from China and declared a state of emergency. In February, eleven municipalities in
northern Italy were identified as the centres of the two main Italian clusters and placed under quarantine. The majority of positive cases in other regions traced back to these two clusters.
[10] On 8 March 2020, Prime Minister
Giuseppe Conte expanded the quarantine to all of Lombardy and 14 other northern provinces, and on the following day to all of Italy,
placing more than 60 million people in lockdown.
[11][12][13] On 11 March 2020, Conte prohibited nearly all commercial activity except for supermarkets and pharmacies.
...}
So then how could anyone not have known?
We successfully quarantined Ebola, so I think we could have handled covid as well.
Seems to me it was deliberately let in.
This is reinforced by the insane decision to "flatten the curve", which means essentially to ensure it lasts the longests, is impossible to end, and that it kills the maximum number of people.