1
00:00:10,500 --> 00:00:14,040
PROFESSOR: So besides
our physical expectation

2
00:00:14,040 --> 00:00:18,570
that a virus such as
SARS-CoV-2, coronavirus,

3
00:00:18,570 --> 00:00:21,990
could be transmitted through
respiratory droplets,

4
00:00:21,990 --> 00:00:24,510
especially aerosol droplets
through the airborne route

5
00:00:24,510 --> 00:00:27,600
of transmission, there
is substantial evidence--

6
00:00:27,600 --> 00:00:31,110
both epidemiological evidence
and some physical evidence--

7
00:00:31,110 --> 00:00:34,490
to support this hypothesis.

8
00:00:34,490 --> 00:00:35,910
So first, let's
go through some of

9
00:00:35,910 --> 00:00:37,110
the epidemiological evidence.

10
00:00:37,110 --> 00:00:41,610
This is a very small fraction
of what is available to date.

11
00:00:41,610 --> 00:00:44,820
So one of the first
incidents that

12
00:00:44,820 --> 00:00:48,660
gave a sense there might
be airborne transmission

13
00:00:48,660 --> 00:00:52,680
was a religious event that took
place at the Tiantong Temple

14
00:00:52,680 --> 00:00:58,050
in Ningbo China, where
there were hundreds

15
00:00:58,050 --> 00:00:59,610
of people in attendance.

16
00:00:59,610 --> 00:01:01,920
But in particular,
there were two buses

17
00:01:01,920 --> 00:01:06,120
that brought worshippers
in one-hour bus rides

18
00:01:06,120 --> 00:01:08,010
to this location.

19
00:01:08,010 --> 00:01:12,300
And on one of the
buses was what was

20
00:01:12,300 --> 00:01:17,130
known to be the first
infected person with COVID-19,

21
00:01:17,130 --> 00:01:20,370
entering this region
after having had contact

22
00:01:20,370 --> 00:01:23,550
with others from Wuhan
China, the initial source

23
00:01:23,550 --> 00:01:25,230
of the outbreak.

24
00:01:25,230 --> 00:01:27,990
And on the bus where
the infected person was,

25
00:01:27,990 --> 00:01:32,970
23 out of 68 passengers became
infected during that ride.

26
00:01:32,970 --> 00:01:35,310
And despite the fact
that there was also

27
00:01:35,310 --> 00:01:37,200
contact in the larger
temple building

28
00:01:37,200 --> 00:01:40,200
with many other people, very
few there were infected.

29
00:01:40,200 --> 00:01:43,410
And on the second bus, where
they kept the same seating,

30
00:01:43,410 --> 00:01:45,060
there were no infections.

31
00:01:45,060 --> 00:01:47,190
So that gave a sense that
on public transportation,

32
00:01:47,190 --> 00:01:51,910
there could be substantial
superspreading going on.

33
00:01:51,910 --> 00:01:55,450
So shortly afterwards, there
were a number of incidents,

34
00:01:55,450 --> 00:02:00,310
including a case in a
restaurant in Guangzhou, China,

35
00:02:00,310 --> 00:02:03,010
where an infected person
was sitting at a table

36
00:02:03,010 --> 00:02:04,930
having dinner with
a party there.

37
00:02:04,930 --> 00:02:08,229
And there was a
documented transmission

38
00:02:08,229 --> 00:02:10,840
to a far corner of
the room with a person

39
00:02:10,840 --> 00:02:13,750
who had not been within a
short distance such as six

40
00:02:13,750 --> 00:02:15,670
feet of the infected
person, had not touched

41
00:02:15,670 --> 00:02:18,960
anything that could have
led to contact transmission.

42
00:02:18,960 --> 00:02:21,130
And it was concluded that
it could only be explained

43
00:02:21,130 --> 00:02:23,650
by airborne transmission.

44
00:02:23,650 --> 00:02:30,100
Then there was a well-known
case involving a cruise ship--

45
00:02:30,100 --> 00:02:31,660
one of several such cases--

46
00:02:31,660 --> 00:02:35,800
of the Diamond Princess
cruise ship, where

47
00:02:35,800 --> 00:02:37,579
a few infections were detected.

48
00:02:37,579 --> 00:02:40,780
And on February
3, 2020, the ship

49
00:02:40,780 --> 00:02:44,630
was quarantined in the
harbor of Yokohama, Japan.

50
00:02:44,630 --> 00:02:50,440
And during that quarantine,
out of 3,011 passengers

51
00:02:50,440 --> 00:02:55,180
and crew on the ship, there were
a total, at the end of 12 days,

52
00:02:55,180 --> 00:02:59,500
of 354 infected
persons, starting

53
00:02:59,500 --> 00:03:02,860
from an initial estimate of--
well, several known cases.

54
00:03:02,860 --> 00:03:06,070
And by our own analysis,
we will be estimating

55
00:03:06,070 --> 00:03:08,590
there were perhaps around
20 initial cases, so

56
00:03:08,590 --> 00:03:11,650
a dramatic increase in the
number of infected persons

57
00:03:11,650 --> 00:03:15,730
in 12 days, despite the fact
that the passengers were mostly

58
00:03:15,730 --> 00:03:19,329
confined to their cabins with
very little movement between.

59
00:03:19,329 --> 00:03:21,940
And also, later analysis
showed that there

60
00:03:21,940 --> 00:03:26,380
was very little statistical
correlation between contact

61
00:03:26,380 --> 00:03:29,320
with an infected person
even being in the same room

62
00:03:29,320 --> 00:03:31,290
and getting a transmission.

63
00:03:31,290 --> 00:03:33,040
In other words,
transmission was happening

64
00:03:33,040 --> 00:03:34,900
between people in
different rooms,

65
00:03:34,900 --> 00:03:37,570
even on different
floors, presumably

66
00:03:37,570 --> 00:03:39,020
through the air handling system.

67
00:03:41,710 --> 00:03:44,500
And among many other
events that followed,

68
00:03:44,500 --> 00:03:47,680
another famous case was
one of the initial sources

69
00:03:47,680 --> 00:03:52,720
of spreading in South Korea was
the Shincheonji Church, which

70
00:03:52,720 --> 00:03:56,890
held services over the
period of February 16 to 25.

71
00:03:56,890 --> 00:04:01,060
And a significant fraction
of thousands of churchgoers

72
00:04:01,060 --> 00:04:06,280
were infected, that led to
the initial outbreak in Korea,

73
00:04:06,280 --> 00:04:09,890
again, coming from contact of a
large number of people sharing

74
00:04:09,890 --> 00:04:12,490
an indoor space, where
it's not possible for each

75
00:04:12,490 --> 00:04:14,650
of those people to have
been touching each other

76
00:04:14,650 --> 00:04:16,690
or within 3 or 6 feet.

77
00:04:16,690 --> 00:04:19,029
But rather, the only
plausible explanation

78
00:04:19,029 --> 00:04:21,470
is transmission through the air.

79
00:04:21,470 --> 00:04:23,290
Another such
example in Korea had

80
00:04:23,290 --> 00:04:25,270
to do with a call
center, where it

81
00:04:25,270 --> 00:04:28,720
was hundreds of people working
in a building with many floors.

82
00:04:28,720 --> 00:04:32,590
And there was an infected
person in one large room of one

83
00:04:32,590 --> 00:04:33,310
of the floors.

84
00:04:33,310 --> 00:04:35,590
And a significant
fraction of the co-workers

85
00:04:35,590 --> 00:04:39,610
were infected in that call
center and yet a relatively

86
00:04:39,610 --> 00:04:42,190
small number in other
parts of the same floor

87
00:04:42,190 --> 00:04:43,930
or on other floors,
again pointing

88
00:04:43,930 --> 00:04:47,980
to airborne transmission
after subsequent analysis.

89
00:04:47,980 --> 00:04:51,730
And then one of the first cases
in the United States famously

90
00:04:51,730 --> 00:04:54,909
occurred in the
Skagit Valley Chorale,

91
00:04:54,909 --> 00:04:57,730
which was holding a
choir practice in Mount

92
00:04:57,730 --> 00:05:00,200
Vernon, Washington, USA.

93
00:05:00,200 --> 00:05:02,770
We will be analyzing
this case in more detail.

94
00:05:02,770 --> 00:05:05,800
But it very dramatically
showed the evidence

95
00:05:05,800 --> 00:05:09,370
for airborne transmission,
because in a 2 and 1/2 hour

96
00:05:09,370 --> 00:05:14,500
choir practice, one infected
person managed to infect 53 out

97
00:05:14,500 --> 00:05:18,760
of 61 others, two
of whom later died,

98
00:05:18,760 --> 00:05:21,190
when it could be
documented that there

99
00:05:21,190 --> 00:05:23,860
was no direct contact,
short-range contact,

100
00:05:23,860 --> 00:05:26,050
or touching between
all of those people.

101
00:05:26,050 --> 00:05:29,110
But rather, they simply
shared the same indoor space.

102
00:05:29,110 --> 00:05:31,270
Also there was a
hint that respiration

103
00:05:31,270 --> 00:05:33,970
and the type of
respiration was important,

104
00:05:33,970 --> 00:05:36,970
in that these
people were singing.

105
00:05:36,970 --> 00:05:38,980
And that led to a
dramatic increase

106
00:05:38,980 --> 00:05:40,480
in the rate of
transmission compared

107
00:05:40,480 --> 00:05:43,990
to other airborne events.

108
00:05:43,990 --> 00:05:46,300
There are many other examples
one could go through.

109
00:05:46,300 --> 00:05:49,270
There have also been,
recently, some meta analyses

110
00:05:49,270 --> 00:05:52,360
of large numbers of
cases, which further

111
00:05:52,360 --> 00:05:56,390
point towards indoor airborne
transmission of COVID-19.

112
00:05:56,390 --> 00:06:01,090
One recent such study
looked at 7,300 cases

113
00:06:01,090 --> 00:06:04,210
of initial spreading
of COVID-19 out

114
00:06:04,210 --> 00:06:08,660
of the epicenter of the outbreak
in Hubei Province, China.

115
00:06:08,660 --> 00:06:12,310
So they looked at 320
cities, to the first known

116
00:06:12,310 --> 00:06:16,720
cases in those cities
outside of Hubei Province.

117
00:06:16,720 --> 00:06:18,460
And they identified
all the clusters

118
00:06:18,460 --> 00:06:21,640
of two or more transmissions.

119
00:06:21,640 --> 00:06:23,200
And of those clusters--

120
00:06:25,960 --> 00:06:27,160
there were 72 of them.

121
00:06:27,160 --> 00:06:29,470
And they all occurred indoors.

122
00:06:29,470 --> 00:06:34,000
And out of those, 80% were at
home in people's apartments.

123
00:06:34,000 --> 00:06:38,980
And 34% also included some
public transportation.

124
00:06:38,980 --> 00:06:40,990
And out of all those
clusters of transmission,

125
00:06:40,990 --> 00:06:43,810
only one was documented
to be occurring

126
00:06:43,810 --> 00:06:48,730
outdoors, consistent with a
wide range of other evidence.

127
00:06:48,730 --> 00:06:51,250
Moreover, there has
been a cataloging

128
00:06:51,250 --> 00:06:54,730
of superspreading events such
as the ones I've listed here.

129
00:06:54,730 --> 00:06:57,970
And that list now
numbers well over 1,000.

130
00:06:57,970 --> 00:07:00,520
And out of all the
superspreading events

131
00:07:00,520 --> 00:07:02,620
that have been
documented, all of them

132
00:07:02,620 --> 00:07:05,560
have occurred indoors and
involving large enough numbers

133
00:07:05,560 --> 00:07:07,900
of people that airborne
transmission is

134
00:07:07,900 --> 00:07:11,150
the most plausible explanation.

135
00:07:11,150 --> 00:07:14,270
So besides the overwhelming
epidemiological evidence

136
00:07:14,270 --> 00:07:16,510
for airborne
transmission of COVID-19,

137
00:07:16,510 --> 00:07:19,110
there is also growing
physical evidence.

138
00:07:19,110 --> 00:07:21,740
So first of all, other
diseases that we've

139
00:07:21,740 --> 00:07:24,440
discussed in this course,
such as tuberculosis,

140
00:07:24,440 --> 00:07:28,880
a bacterial disease, measles
and the original SARS-CoV

141
00:07:28,880 --> 00:07:32,090
coronavirus, which
are viral diseases,

142
00:07:32,090 --> 00:07:34,970
have all been
established and believed

143
00:07:34,970 --> 00:07:40,530
to be transmitted through
respiratory aerosols.

144
00:07:40,530 --> 00:07:44,510
SARS-CoV-2 is a very similar
coronavirus to SARS-CoV-1.

145
00:07:44,510 --> 00:07:47,659
And so it's plausible that
its mechanism of transmission

146
00:07:47,659 --> 00:07:51,320
would be the same,
if not similar.

147
00:07:51,320 --> 00:07:55,850
And indeed, there has been
recent work demonstrating

148
00:07:55,850 --> 00:07:57,860
that infectious
aerosol droplets could

149
00:07:57,860 --> 00:08:02,600
be isolated from infected
patients with COVID-19.

150
00:08:02,600 --> 00:08:06,110
And in particular, the
most infectious droplets

151
00:08:06,110 --> 00:08:07,910
observed were in
the aerosol range

152
00:08:07,910 --> 00:08:11,180
with radii less than 2 microns.

153
00:08:11,180 --> 00:08:14,900
So the evidence is
growing and frankly

154
00:08:14,900 --> 00:08:18,650
becoming overwhelming that the
airborne route of transmission

155
00:08:18,650 --> 00:08:21,890
is important, if not
dominant, for COVID-19.

156
00:08:21,890 --> 00:08:24,950
So we will continue
now by analyzing

157
00:08:24,950 --> 00:08:30,020
how to mitigate and
model the transmission

158
00:08:30,020 --> 00:08:33,909
of a respiratory
pathogen indoors.