Here's an international report on this issue

ABUJA — South Africa and Nigeria are embroiled in a diplomatic spat after the authorities at Johannesburg airport deported 125 Nigerians, alleging their yellow fever vaccination certificates were fakes — the latest twist in a long-standing rivalry between Africa’s two biggest economies.  

Nigeria has responded with undisguised tit-for-tat deportations of 84 South Africans in the past two days, according to a senior official at the State Security Service who could not be named.  

“South Africans will know we are very serious with this matter and that any deportation of any Nigerian, we will meet it with equal reciprocal measure,” Foreign Minister Olugbenga Ashiru told a hearing at the National Assembly late on Tuesday.  

“What you see playing out is ... xenophobia by South Africans against all Africans, not just Nigerians, including even those from their neighbouring countries,” he said.  

A spokesman for South Africa’s home affairs department said the decision to deport the Nigerians stemmed purely from concerns about health.   

“It’s not an immigration issue, it’s a health matter ... Nobody without a yellow fever certificate is allowed into the country and that’s what this is,” said Ronnie Mamoepa.  

Cards proving vaccination against yellow fever — a deadly mosquito-borne disease — are required by most African countries for entry. But they sometimes serve as a lever for immigration officials to obstruct travel or extort bribes.  

Olugbenga warned that Nigeria could take broader retaliatory measures, including a clampdown on South African companies.  

“Their companies here in Nigeria are making more profit than in South Africa. They bring in half-baked graduates and place them above better qualified Nigerians, and we have been overlooking that before now. There are many ways to hit back,” he told the Senate.  

Nigeria is the biggest market for South Africa’s MTN mobile operator. South Africa’s Shoprite and Standard Bank Group also have profitable operations in Nigeria.     

Nigeria and South Africa have been at odds diplomatically at the African Union several times, including over the conflicts sparked by former Libyan leader Muammar Gaddafi’s and Ivory Coast president Laurent Gbagbo’s bids to stay in power last year.  

South Africa backed Gbagbo and Gaddafi as counterweights to Western hegemony, even when the two men began killing opposition demonstrators, while Nigeria backed intervention to oust them.  

Forged yellow fever vaccination certificates are easy to buy from hawkers at Lagos airport.  

Unlike many African countries, relatively developed South Africa has the facilities to check whether they are fake.