What are the various Covid-19 vaccines being used in SA and how well do they work?

As the Covid-19 vaccine roll-out ramps up, it is useful to get a good understanding of the various vaccines planned for South Africa and how well they work.

The most important thing to understand is that vaccination does not confer instant immunity. The full effect is reached two weeks after the final dose. There is variation between vaccine types in the number of doses and efficacy of the first dose.

The Johnson & Johnson vaccine requires a single dose. Two weeks later, you have its maximum protection.

The Pfizer vaccine requires two doses but confers a reasonable degree of immunity two weeks after the first dose. CoronaVac, also called the Sinovac COVID-19, is based on inactivated SARS-Cov-2 virus, and has very little effect after one dose; 2 weeks after the second dose, immunity is reasonably strong.

Why does all this matter?

Chile is a salutary example of getting it wrong (as reported in BMJ in April). More than 90% of the vaccines administered there were Sinovac, and the government erred in encouraging the belief that the pandemic was over once you were vaccinated. A study shows that Sinovac confers only 3% protection after the first dose so the message should have been: wait until two weeks after your second dose.

Does this mean Sinovac is an inferior vaccine? This kind of performance is standard for a dead virus vaccine, which typically needs at least two doses. Pfizer and Johnson & Johnson overall have better efficacy but, in the interests of a faster roll-out, we should take what we can get.

The lesson for South Africa? Information should be clear on when you are relatively safe, particularly with Sinovac. The Pfizer vaccine, while a lot better after two doses, does give some protection after one dose.

How much difference does vaccination make? Over the past week, the United Kingdom had about 170 000 cases and South Africa about 130 000 — about three-quarters of the UK total. In the same period the UK recorded about 200 deaths and South Africa had nearly 2 500. At the time I checked these numbers, just over 50% of the UK population was fully vaccinated; about 2% of people in South Africa were. South Africa has more than 15 times the UK’s case fatality rate.

Although the UK is doing relatively well and is running the occasional full-capacity sporting event such as the Wimbledon finals, some argue that they are opening up too fast. Deaths are more under control than before, but a rapid rise in infections creates the risk of yet another variant arising, which may be more resistant to vaccines or that escapes previous immunity.

In South Africa, we should be pushing hard to increase the rate of vaccination. Though the UK strategy of opening while infections are still high is questionable, being ahead on vaccinating is definitely a plus.

Is it a good strategy to have a mix of vaccines? I have not seen any studies that look at this society-wide. But there is a growing body of evidence that a second dose of a different vaccine gives stronger immunity boost than two doses of one vaccine. This arises from the fact that each vaccine differs in the exact immune response it stimulates, so two vaccines cover more variability in the virus. The same could apply to a society that uses multiple vaccines: if a variant escapes one vaccine, it may be stopped to some degree by another.

If you want to check if your vaccine worked, can you use the antibody test for SARS-CoV-2 infection? No. The nucleocapsid (N) protein, which plays a major role in packaging the viral genome, is a target of antibodies that the standard antibody tests pick up. The N protein has to be present in the virus. But it is not part of the vaccines currently in use in South Africa. If you want to check if a vaccine has triggered an immune response, you need a different test that checks for antibodies to the spike protein (S), which should be present in all vaccines.

What of those who have already contracted Covid-19? The general advice in South Africa (advice varies around the world) is to wait four weeks after symptoms clear before vaccinating; in this case, the vaccine acts as a booster, and only one dose should be necessary.

Those with compromised immune systems have been a small part of vaccine trials; the early evidence is that they may need an extra booster dose to get effective protection.

There is some evidence that lingering symptoms may be cleared by a vaccination, though long Covid — symptoms that go on for an extended time — is still the subject of research. One plus about this condition is it has similarities to myalgic encephalomyelitis (ME), also called chronic fatigue syndrome.  Research into long Covid may help long-suffering ME patients, whose condition has not had the attention it deserves.

Discovery Health has reported on their statistics for vaccinated clients  from 17 May to 29 June, aged 60 or over, 21 days after their first Pfizer dose. For 141 646 who received one Pfizer dose countrywide, they report one hospital admission arising from the vaccine. Most adverse effects they report are relatively mild — a headache or mild fever.

What of preventing serious illness? The Discovery survey in this area focuses on 46 000 of their members in Gauteng: there were 49 Covid-related hospital admissions for those who were vaccinated and 85 for an unvaccinated group of a similar size.

These numbers are promising, given that the Pfizer vaccine achieves maximum protection 14 days after the second dose — particularly as those aged over 60 are more vulnerable.

A high rate of vaccination is not only the recipe for early opening but for reducing the odds of another even more contagious variant arising. In the meantime, we need to keep taking nonpharmaceutical interventions seriously, particularly masking, distancing and ventilation.

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Philip Machanick
Philip Machanick is an associate professor of computer science at Rhodes University

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