Covid-19: Omicron sublineages likely evade vaccines, natural immunity

Johannesburg: New Omicron sublineages, discovered by South African scientists this month, are likely able to evade vaccines and natural immunity from prior infections, the head of gene sequencing units that produced a study on the strains said.

The BA.4 and BA.5 sublineages appear to be more infectious than the earlier BA.2 lineage, which itself was more infectious than the original Omicron variant, Tulio de Oliveira, the head of the institutes, said.

With almost all South Africans either having been vaccinated against the coronavirus or having had a prior infection the current surge in cases means that the strains are more likely to be capable of evading the body’s defenses rather than simply being more transmissible, de Oliveira said.

There are "mutations in the lineages that allow the virus to evade immunity," he said in a response to queries. "We expect that it can cause reinfections and it can break through some vaccines, because that’s the only way something can grow in South Africa where we estimate that more than 90% of the population has a level of immune protection."

Early warning

South Africa is seen as a key harbinger of how the Omicron variant and its sublineages are likely to play out in the rest of the world. South African and Botswanan scientists discovered Omicron in November and South Africa was the first country to experience a major surge of infections as a result of the variant.

The new sublineages account for about 70% of new coronavirus cases in South Africa, de Oliveira said in a series of Twitter postings.

"Our main scenario for Omicron BA.4 and BA.5 is that it increases infections but that does not translate into large hospitalizations and deaths," he said.

South Africa recorded 4,146 new cases with a test positivity rate of 18.3% on Thursday. That compares with 581 cases and a positivity rate of 4.5% on March 28. Waasila Jassat, a public health specialist at the National Institute of Communicable Diseases, said ona conference call that hospitalizations are rising but there is yet to be a significant rise in deaths.

The sublineages have been detected in seven of South Africa’s nine provinces and 20 countries worldwide.

"There is quite a lot of diversity in this Omicron family of lineages," Richard Lessells, an infectious disease specialist at the KRISP genomics institute, said on the conference call on Friday. This could explain why the newly identified sublineages are causing an upsurge infections, he said.