Discovery Health says the transmission efficacy of a double-dose Pfizer vaccine against Covid-19 has fallen to 33%. The Pfizer vaccines had been 80% effective against preventing infections during the previous Covid-19 variants.
Discovery Health collected data from its members’ vaccination records, Covid-19 tests, pathology results and anecdotal evidence from hospital groups, including Mediclinic. The study included about 78 000 Covid-19 test results for Omicron infections from 15 November to 7 December.
The health insurer said the Omicron variant dominates infections and is currently responsible for more than 90% of cases in South Africa.
The pathology records showed that fully vaccinated people who took the Pfizer jabs still have a 56% chance of avoiding Omicron infection after two to four weeks of getting their second dose. But after three to four months after the second dose, the vaccine’s effectiveness against Omicron falls to 25%.
“During this period, we do see many breakthrough infections, and the vaccine effectiveness has reduced quite materially. And so, you know, social distancing behaviours, mask wearing, and caution and prudence are critically important,” said Discovery Health CEO Dr Ryan Noach.
However, the Discovery data shows that people are recovering from the virus much quicker – within three to four days.
The most common symptoms of Omicron are also less severe. It’s usually scratchy or sore throat, similar to the other waves. But that’s usually followed by nasal congestion, dry cough, and mild lower back pain, whereas people mostly complained of shortness of breath and other more severe symptoms with the previous variants.
Hospitalisation of vaccinated people has reduced materially
Noach said while this is quite a material reduction in the vaccine’s efficacy, it’s critical to remember that the jabs were primarily developed to prevent severe illness and death. And the data shows that they still do that job well under the Omicron wave.
Vaccinated individuals are presenting milder symptoms, and it is predominantly unvaccinated people that are being hospitalised. Noach said the Pfizer vaccine is still 70% effective in mitigating hospital admissions.
There’s also bad news for people who aren’t vaccinating because they believe that they’ve built immunity as a result of prior infection.
“What we do see is that the protective effects of prior infection in the previous waves of Covid-19 have reduced over time. And now in this Omicron period, we’ve seen further erosion of that protective effect,” added Noach.
But if a fully vaccinated person ever lands up in a hospital, clinicians report that they stay for a much shorter period, said Prof Glenda Gray, the president and CEO of the South African Medical Research Council.
Gray added that the Sisonke study data and other experiences from the National Institute For Communicable Diseases corroborate Discovery Health in this regard. Vaccinated healthcare workers under the Sisonke study stay in hospital for around 2.4 days.
“Most people in hospitals are unvaccinated. But we need to continue to watch how this virus plays out and whether the initial low impact on hospitalisation persists,” she said.
Gray said it was too early to conclude that the hospitalisation picture in SA will remain this way and that other countries will experience the same because of nuances in this country that may not be present in others.
Discovery estimates that about 70% of people in SA have been exposed to the virus already. Gray said in some parts of SA, up to 80% of people were exposed to the virus after the Delta variant. This high prevalence of prior infections, together with almost 40% vaccination coverage, could be the reason that the Omicron wave appears to be delinked from severe infections and hospitalisation.
“However, we don’t know how Omicron is going to evolve in countries where there’s low vaccination rates or low prior infection rates … So we would be very cautious to try and interpret that this may be a less virulent strain. We’d have to see what happens in other parts of the world,” she added.
What about J&J vaccines?
Discovery Health didn’t share insights into the effectiveness of the Johnson & Johnson vaccine against Omicron. But Gray said she and her team were monitoring breakthrough infections.
She said there have been many breakthrough infections among healthcare workers who are part of the Sisonke study, but very little hospital admission compared to the Delta wave.
“As of today, we’ve had no one who’s died from Omicron from the J&J study. So that’s good news. It shows again that the vaccine is effective against severe disease and death, and that’s very reassuring,” said Gray.
She said she and her research team will be finalising the analysis of the J&J vaccine effectiveness in the next couple of days.
Healthcare workers in the Sisonke study have been offered booster vaccines. Gray said the researchers will now be able to compare the results of the Sisonke participants who got the booster dose to those who have not taken it to the impact of the second dose on Omicron.
Noach and Gray said the rollout of Covid-19 booster shots will be critical to keeping reinfection rates down in SA.