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«Herd immunity remains the final objective», according to Moroccan epidemiologist Youssef Oulhoute

Containment, deconfinement, spread, R0, Rt, vaccine, herd immunity, pulmonary embolism, hydroxychloroquine... We have all become familiar with this vocabulary amid the coronavirus crisis. However, we have never been so aware of the weakness of our knowledge in epidemiology. To better understand the situation, Yabiladi interviewed Moroccan epidemiologist and researcher at the University of Massachusetts in the United States Youssef Oulhoute.

Moroccan researcher and epidemiologist Youssef Oulhote. / DR
Estimated read time: 4'

Two recent coronavirus studies have suggested that immunity after infection exists and can be robust. Can you explain how ?

A study regarding this possibility is underway (preprint), but it has not been peer-reviewed yet. The other study, on the other hand, was published by peer-reviewed journal Cell. The two studies share the same conclusions. What is important to remember is that all infected people have produced an immune response (production of CD4 + cells) that is capable of triggering a humoral reaction, hence the possibility of producing antibodies against SARS-CoV-2.

What is specific to the cases studied is that this immune reaction has been observed among benign Covid-19 infections. Better yet, it has been found that, in a second group which has not tested positive, there is also a presence of this immune response.

This explains, only on a hypothetical level, the few infections recorded among children. Being often exposed to colds, they have been able to develop immune reactions which continue to protect them from several coronaviruses. This is called «cross-immunity». The same thing applies to asymptomatic cases.

This discovery shows that it is not necessary to have a significant infection rate within the population to achieve the so-often-called herd immunity. The heterogeneity of the transmission and the existence of cases of super-spreading also point towards this direction where it would appear that less than 20% of the infected are responsible for 80% of secondary infections.

Betting on herd immunity is however a difficult choice, especially for vulnerable communities. Where are we now ?

Herd immunity remains the ultimate goal. Very few people dare to say it, but that is what will save us in the end, whether it is with or without a vaccine. However, finding a vaccine is a means to achieve herd immunity. The problem with the strategy of letting the virus spread to achieve herd immunity is sacrificing many lives, while at the same time overloading hospitals.

Sweden is a good example of that. They decided not to implement a mandatory lockdown and bet on herd immunity. The result was that mobility in Sweden has declined in the same way as in other countries.

In a country like Morocco, implementing the same strategy of herd immunity would have dire economic and sanitary consequences.

President Donald Trump and Moncef Slaoui. / Ph. Drew Angerer -AFPPresident Donald Trump and Moncef Slaoui. / Ph. Drew Angerer -AFP

There have been announcements of promising vaccine discoveries. Can we hope for a vaccine by the end of the year, as Moncef Slaoui announced to Donald Trump ?

There are indeed a hundreds of vaccines that are being studied currently, including 6 or 7 which are in the advanced stage of clinical trial.

Historically, developing a vaccine has taken an enormous amount of time. We can find a promising vaccine, but clinical trials can last from 4 to 7 years.

In general, a vaccine is the modified virus from which its infectious part is removed, but for Moderna, which has just made a very optimistic announcement, the vaccine uses a strand of RNA.

The biggest challenge will be the logistical capacity to mass produce. Countries that do not have this technology will not be able to produce the vaccine, as it is hard to adapt the conventional vaccine industry.

How do you assess the epidemiological situation in Morocco ?

To assess the epidemiological situation, it is necessary to have access to detailed data. We talk about R0 (propagation rate), Rt but these are only average rates which are difficult to interpret without the context. 

There is a tendency to trust a single indicator, but this is a mistake. Once the objective is an indicator, for example the R0, it is no longer a good indicator, because it can be manipulated in different ways.

From my point of view, we need several indicators: the Rt by calculating it in different ways to see if the different results converge; the rate of positive tests on the total number of tests carried out or positivity rate which must be greater than 50 for example. These different indicators are rather reassuring for Morocco. But ultimately, the deconfinement question is not about when but how.

What would be the best practice for deconfining ? Is there a range of effective measures like mass testing, tracing via smartphone, and so on...?

If we could do mass testing, we can end the lockdown quickly. The concern is that Morocco simply does not have enough capacity, because we do not have national production. This is also food for thought: why do we not have such an industry when it is not particularly complicated?

But given the current context, we have to adapt by doing something else. So the tracing app is useful but it requires a high adoption rate, managing false positives, and having the rapid intervention capacities for the management of suspected cases. There is also virus surveillance in wastewater, and making sure that the the sentinel network to monitor influenza-like illness is properly used.

Has hydroxychloroquine + azithromycin played a role in treating severe cases ?

There is no proven causal link. It is a disease that will kill an average of 1%, probably less in Morocco since the average age of the infected is less than 40 years. So to put it in other words, out of 100 infected people, 99 will recover. 85 of them will heal just by drinking water because they will have no complications.

All serious studies to date have not proven the effectiveness of this treatment. It could even have serious side effects. Antivirals are not really the miracle treatment. Neither hydroxychloroquine nor Remdesevir is the solution.

Coronavirus cases
142 097 803
Confirmed Covid-19 cases
3 029 811
total deaths
81 306 846
total recovered
 
Cases
Deaths
USA
31 737 347
567 690
India
15 320 972
180 530
Brazil
13 973 695
374 682
France
5 357 229
101 339
Russia
4 657 509
104 173
United Kingdom
4 406 114
127 524
Turkey
4 323 596
36 267
Italy
3 878 994
117 243
Spain
3 428 354
77 102
Germany
3 167 137
80 353
Argentina
2 714 475
59 476
Poland
2 695 327
62 133
Colombia
2 667 136
68 748
Mexico
2 306 910
212 466
Iran
2 261 435
67 130
Ukraine
2 006 197
41 755
Peru
1 707 787
57 537
Indonesia
1 609 300
43 567
Czechia
1 602 711
28 532
South Africa
1 567 513
53 757
Netherlands
1 435 601
17 150
Canada
1 139 591
23 649
Chile
1 131 340
25 277
Romania
1 031 072
26 381
Iraq
984 950
15 026
Belgium
951 626
23 782
Philippines
945 745
16 048
Sweden
900 138
13 788
Israel
837 218
6 341
Portugal
831 221
16 946
Pakistan
766 882
16 453
Hungary
753 188
25 381
Bangladesh
723 221
10 497
Jordanie
689 482
8 308
Serbia
664 972
6 026
Switzerland
637 304
10 521
Austria
595 540
9 922
Japan
537 494
9 629
Lebanon
511 398
6 959
Morocco
505 949
8 952
United Arab Emirates
498 957
1 556
Saudi Arabia
405 940
6 834
Bulgaria
388 815
15 412
Malaysia
377 132
1 386
Slovakia
376 067
11 172
Panama
361 044
6 189
Ecuador
360 563
17 703
Belarus
345 110
2 433
Kazakhstan
344 140
3 294
Greece
316 879
9 540
Croatia
308 200
6 601
Azerbaijan
301 661
4 169
Georgia
295 936
3 949
Bolivia
290 362
12 666
Tunisia
287 061
9 825
Nepal
285 900
3 091
West Bank and Gaza
282 270
3 047
Dominican Republic
261 531
3 422
Kuwait
258 497
1 456
Paraguay
252 443
5 384
Moldova
246 238
5 591
Denmark
244 067
2 460
Ireland
243 911
4 836
Ethiopia
243 631
3 392
Lithuania
234 232
3 770
Slovenia
232 311
4 167
Costa Rica
230 837
3 099
Egypt
217 186
12 778
Guatemala
213 049
7 241
Armenia
208 818
3 895
Honduras
201 677
4 963
Qatar
197 476
386
Bosnia and Herzegovina
191 154
7 938
Venezuela
184 595
1 925
Oman
181 430
1 890
Libya
172 464
2 908
Uruguay
167 033
1 971
Bahrain
165 118
600
Nigeria
164 303
2 061
Kenya
151 894
2 501
North Macedonia
147 229
4 478
Burma
142 644
3 206
Albania
129 694
2 347
Algeria
119 805
3 160
Estonia
117 782
1 100
Korea, South
115 195
1 802
Latvia
111 536
2 056
Norway
108 028
709
China
102 264
4 845
Kosovo
101 191
2 080
Sri Lanka
97 105
620
Montenegro
95 695
1 438
Cuba
94 571
531
Kyrgyzstan
92 095
1 555
Ghana
91 709
771
Zambia
90 942
1 236
Uzbekistan
86 982
638
Finland
84 287
891
Mozambique
69 228
800
El Salvador
67 557
2 078
Luxembourg
65 144
786
Cameroon
64 809
939
Singapore
60 851
30
Afghanistan
57 898
2 546
Cyprus
57 081
294
Namibia
46 773
604
Cote d'Ivoire
45 570
274
Botswana
44 702
684
Jamaica
44 136
727
Thailand
43 742
104
Uganda
41 396
339
Senegal
39 821
1 091
Zimbabwe
37 859
1 553
Malawi
33 959
1 139
Sudan
33 022
2 281
Madagascar
32 798
552
Malta
30 026
409
Australia
29 556
910
Congo (Kinshasa)
28 956
745
Maldives
26 505
70
Angola
24 518
563
Mongolia
24 195
51
Rwanda
23 934
326
Gabon
22 032
136
Guinea-Bissau
21 612
138
Syria
21 279
1 456
Cabo Verde
20 627
193
Eswatini
18 417
671
Mauritania
18 142
454
Somalia
13 324
678
Tajikistan
13 308
90
Burkina Faso
13 148
154
Mali
13 145
441
Haiti
12 918
251
Andorra
12 805
123
Belize
12 558
318
Togo
12 553
120
Guyana
11 901
271
Lesotho
10 720
316
Djibouti
10 510
119
South Sudan
10 473
114
Congo (Brazzaville)
10 084
139
Papua New Guinea
9 952
91
Bahamas
9 791
194
Suriname
9 581
187
Trinidad and Tobago
8 964
154
Benin
7 611
95
Equatorial Guinea
7 259
106
Cambodia
7 013
45
Nicaragua
6 778
180
Iceland
6 329
29
Yemen
5 858
1 132
Central African Republic
5 787
75
Gambia
5 720
170
Niger
5 131
190
San Marino
5 030
88
Seychelles
4 976
25
Chad
4 708
169
Saint Lucia
4 419
69
Sierra Leone
4 038
79
Comoros
3 819
146
Barbados
3 784
44
Guinea-Bissau
3 712
66
Eritrea
3 537
10
Burundi
3 477
6
Liechtenstein
2 823
56
Vietnam
2 791
35
New Zealand
2 597
26
Monaco
2 404
31
Sao Tome and Principe
2 275
35
Liberia
2 042
85
Saint Vincent and the Grenadines
1 819
10
Timor-Leste
1 368
2
Antigua and Barbuda
1 217
31
Mauritius
1 203
15
Taiwan*
1 076
11
Bhutan
961
1
Diamond Princess
712
13
Tanzania
509
21
Brunei Darussalam
221
3
Dominican Republic
165
0
Grenada
157
1
Fiji
72
2
Laos
58
0
Saint Kitts and Nevis
44
0
Holy See
27
0
Solomon Islands
20
0
MS Zaandam
9
2
Marshall Islands
4
0
Samoa
3
0
Vanuatu
3
0
Micronesia
1
0
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