Could herd immunity explain Senegal's low COVID-19 cases?

Senegal has been widely praised for its handling of the coronavirus pandemic, with few infections and life returning to normal, but the reason behind its success still divides experts.

The government enacted a raft of anti-virus measures when the pandemic reached the West African nation. But some experts believe that herd immunity may explain the low level of cases.

With a mostly youthful population of some 16 million people, the country has recorded some 16,000 coronavirus cases and 331 deaths to date, according to the health ministry.

Like many African countries, Senegal would have racked up many thousands of deaths had it experienced an outbreak similar to the kind that ravaged Europe and the United States.

Senegal is "one of the model countries in terms of implementing Covid-19 prevention measures and it has reaped the benefits," World Health Organization official Nsenga Ngoy said during a virtual press conference this month.

The government closed its borders, schools and mosques when the virus first hit in March, as well as banning large gatherings and travel between cities, and imposing a night-time curfew.

It also undertook medical care for ailing COVID-19 patients, and aggressively isolated people who had come into contact with positive cases.

Authorities encouraged mask-wearing and social distancing too, measures that Ngoy said would continue to play a key role in keeping infections at bay.

Abdoulaye Bousso, one of the government officials in charge of Senegal's coronavirus response, said that the measures staved off a collapse of the country's health system.

Herd immunity hypothesis

Mysteriously, however, Senegal has been registering fewer cases despite lifting its anti-virus measures -- and despite the fact that mask-wearing and social distancing have slackened considerably.

The Islamic festival of Eid al-Adha in July saw swathes of the country travel to their home towns to celebrate with their families -- without a discernible effect on infection rates.

Likewise for last month's "Magal" religious festival, which saw hundreds of thousands of pilgrims descend on Senegal's second largest city Touba.

Referring to the Islamic festivals, Bousso told AFP that "perhaps the question of immunity needs to be brought to the fore".

Massamba Sassoum Diop, the head of the emergency-healthcare organisation SOS Medecins Senegal, agreed.

"We are aware that in Africa in general, and in Senegal in particular, we don't have the deaths we should have had," he said.

The doctor is convinced that a substantial part of the population has already acquired immunity, and estimated that proportion at around "60 percent".

The virus swept through Senegal's mostly young population between March and August, Diop suggested, offering an immunity that may explain the decline in deaths and infections.

He pointed out that most recorded infections are in people between 20 and 60 years old, and that it is patients older than 65 who are most likely to die of COVID-19.

"It spread around the country, we're sure," Diop said, explaining that about 30 percent of COVID-19 tests in Senegal used to return positive results, compared to roughly one percent now.

'Pessimistic hypothesis'

Diop acknowledged that the herd-immunity hypothesis is unproven, but said a serological study underway in Senegal could provide answers when it is released in several weeks.

Health Minister Abdoulaye Diouf Sarr disagrees that herd-immunity is a factor.

He told reporters on Tuesday that Senegal's low case numbers are "without a doubt due to the (government's) response".

"If herd immunity were the response, the corollary would be an extremely high number of deaths," he said.

Senegalese health experts, and the World Health Organization, are also warning against an overly optimistic interpretation of the virus situation in the country.

And the government continues to urge vigilance. Health Minister Sarr said that current research available suggests that Senegal will be spared a second wave of infections.

"But we are still working under what is known as the pessimistic hypothesis," he said.