Pfizer vaccine provides high level of protection against severe disease - SAMRC/Discovery Health study

While two doses of the Pfizer vaccine offered much lower protection against infection with the Omicron Covid-19 variant, it still offered solid resistance when it came to severe disease, a study by Discovery Health and the South African Medical Research Council (SAMRC) has found.

In their latest update on the current outbreak of coronavirus infections in South Africa, the National Institute for Communicable Diseases (NICD) said the positivity rate in the country was still increasing and had reached 34.9%, meaning that more than one in three tests conducted are returning a positive result for the virus.

The current wave of infections is driven by the Omicron variant, which has been declared a variant of concern by the World Health Organization.

According to the NICD, there is still no end in sight for rising cases in the country. Between Monday and Tuesday, another 23,884 positive cases were registered in South Africa, and another 24 Covid-19-related deaths.

The bulk of the new cases was registered in Gauteng, with 8,685 new cases, followed by KwaZulu-Natal with 5 205 and the Western Cape with 3,180.

Discovery Health, South Africa’s largest private healthcare administrator, said numbers show that the two-dose Pfizer vaccine provided 70% protection against severe complications of Covid-19 requiring hospitalisation and 33% protection against Covid-19 infection during the current Omicron wave.

According to Discovery’s data, the reinfection risk for individuals who have had Covid-19 previously is significantly higher when exposed to Omicron.

“The risk of hospital admission among adults diagnosed with Covid-19 is 29% lower for the Omicron variant infection compared to infections involving [the first variant] that drove South Africa’s first wave in mid-2020, after adjusting for vaccination status,” it said.

Discovery’s data also showed that despite low absolute incidence, preliminary data suggest that children have a 20% higher risk of hospital admission in the Omicron-led fourth wave in South Africa, relative to the first wave.

“It is important to note that these insights relate to data from the first three weeks of the Omicron-driven wave in South Africa. Therefore, the insights should be considered preliminary, since they may change as the wave progresses. This data are also confounded by various factors, including high seroprevalence of Covid-19 antibodies in the South African population as a whole,” Discovery said.

“Superb genetic surveillance by the Network for Genomic Surveillance in South Africa identified that Omicron infection accounts for more than 90% of new infections in South Africa, and has displaced the formerly dominant Delta variant,” said Dr Ryan Noach, CEO of Discovery Health.

“The Omicron-driven fourth wave has a significantly steeper trajectory of new infections relative to prior waves. National data show an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection,” he added.

Discovery Health partnered with the SAMRC to provide insights into the effectiveness of the Pfizer vaccine against infections and severe disease linked to the Omicron variant and found that it provided significant protection against hospitalisation in individuals with Omicron. Their study was based on 211,000 Covid-19 test results.

The results of the study are in line with similar research done by Pfizer itself, released last week. The company indicated that a third shot of the vaccine will considerably increase protection.

Another study by the Africa Health Research Institute in KwaZulu-Natal also found that Omicron can escape some of the immune responses triggered by the vaccine but not all.

President of the SAMRC, Professor Glenda Gray, said, “We are extremely encouraged by the results of Discovery Health’s analysis. It is extremely important to be able to demonstrate to the public that in a real-world setting – in the presence of a highly transmissible new Covid-19 variant – the Pfizer vaccine provides good protection against severe disease and hospitalisation.”

According to the results of the study, the protection afforded by the vaccine against hospital admission is maintained across all ages, in people from 18 to 79 years, with slightly lower levels of protection for the elderly (67% in people aged 60 to 69 and 60% for people aged 70 to 79). Protection against admission is also consistent across a range of chronic illnesses, including diabetes, hypertension, hypercholesterolemia and other cardiovascular diseases.

“With each successive wave of Covid-19 infection in South Africa, we have investigated the durability of immunity following previous infection with Covid-19 – in other words, the risk of reinfection,” said Shirley Collie, who headed the actuarial team in the Discovery/SAMRC study.

“Overall, the risk of re-infection [following prior infection] has increased over time, with Omicron resulting in significantly higher rates of reinfection compared to prior variants.”

She said people who were infected with Covid-19 in South Africa’s third [Delta] wave face a 40% relative risk of reinfection with Omicron and people who were infected with Covid-19 in South Africa’s second wave face a 60% relative risk of reinfection with Omicron.

“People who were infected in South Africa’s first wave face a 73% risk of reinfection relative to those without prior documented infection,” Collie said. 

Discovery’s Noach said they have noted that while there is a steep trajectory of new infections, the rate of hospitalisation is much less.

“This lesser severity could, however, be confounded by the high seroprevalence levels of SARS CoV-2 antibodies in the general South African population, especially following an extensive Delta wave of infections,” he said.

“Notwithstanding the fact that children continue to show a very low incidence of severe complications following Covid-19, Discovery Health’s data indicate that children under age 18 have a 20% higher risk of admission for complications of Covid-19 when infected with Omicron,” Collie added. 

“This is early data and requires careful follow-up. However, this trend aligns with the warning from South Africa’s NICD in recent days that during South Africa’s third wave of infection [June to September 2021] they had seen an increase in pediatric admissions and now, in the fourth wave, they are seeing a similar increase in admissions for children under five years of age,” Collie continued.

“Anecdotal reports from hospitals in South Africa indicate that most Covid-19 diagnoses in children admitted to hospital are coincidental – many children who are admitted for non-Covid-19-related conditions, and who are not experiencing Covid-19 complications, test positive for Covid-19 on routine screening tests,” she added.

“Children were 51% less likely to test positive for Covid-19 relative to adults in the Omicron period and, overall, the risk of children being admitted to hospital for Covid-19 complications remains low.”

Commenting on anecdotal reports sourced from treating healthcare professionals, Noach added, “The majority of children present with mild disease, with symptoms such as a sore throat, nasal congestion, headache and fever that resolves within three days.” DM/MC