Although each Covid-19 vaccine is unique, clinical trial data and real-world evidence continue to show that all of them offer strong protection against severe disease, hospitalisation, and death.
This includes the single-dose Johnson & Johnson (J&J) vaccine. A primary analysis of the Sisonke Covid vaccine trial, which involved close to 500 000 South African health workers, looked at the safety and impact on the variants of concern, including the highly transmissible Delta variant.
The researchers of the study have also been monitoring breakthrough infections (when a fully vaccinated person gets infected with Covid).
“None of our vaccines is 100% prophylactic, so they do not stop all infections, but what this data shows is that in Sisonke we have seen breakthrough infections but the vast majority have been asymptomatic or at worst, mild,” said Professor Linda-Gail Bekker, co-investigator on the trial.
Bekker was speaking at a virtual webinar hosted by UCT last Thursday.
A small number of cases were classified as moderate infection, where participants might have needed to be hospitalised, but did not require oxygen or intensive care. An even smaller number of cases (0.48%) were severe, she said. There were also 53 breakthrough infections (0.4%) where the recipients died due to Covid. In the majority of these cases, participants were aged 50 to 64 years and had at least one comorbidity.
“You’re seeing very good protection against death and reasonable protection against hospitalisation. When we compare the period of time where we had Beta and Delta circulating, we do not see a difference in terms of the effectiveness of the vaccine,” said Bekker.
“This was a large study and I think we will continue to see good data coming out of this,” she added.
Addressing vaccine hesitancy
Also on the panel was Professor Koleka Mlisana, co-chair of South Africa’s Ministerial Advisory Committee (MAC) on Coronavirus, who addressed the topic of vaccine hesitancy in SA.
“When we talk about whether to vaccinate or not to vaccinate, I think it all revolves around vaccine acceptance … We need to ask what are some of the vaccine-related fears,” she said.
Globally, a recent systematic review showed a declining global vaccine acceptance, from more than 70% acceptance in March 2020 to under 50% in October 2020, she said.
In SA, Covid vaccine acceptance ranged from 52% to 82%, while an outright non-willingness to take the vaccine stood at under 20%, she said.
Some of the concerns of South Africans about the Covid vaccines include safety of the vaccines (such as any worrying side effects); the efficacy; the thoroughness of the development of the vaccines; the ability of the government to roll out the vaccine programme, which had some hiccups and has led to a decrease in public trust; and myths and conspiracy theories about the vaccines, she said.
Mlisana stressed that communication is key in combating hesitancy. “We need to understand people’s concerns and see how best to address them, and they’ve got to be appropriate for different communities,” she said.
Viral load: vaccinated vs unvaccinated
Since vaccinated individuals are still able to transmit the virus, it has been used as an argument by anti-vaxxers and some vaccine sceptics as a reason not to get vaccinated against Covid.
Addressing the topic of viral loads, Professor Shabir Madhi said: “A lot has been made that people who are vaccinated that end up with breakthrough infections have similar viral loads as unvaccinated people, and with the Delta variant it might even be slightly higher. That is true. [And] some would use this as an argument as to why people that have breakthrough infections are as likely to transmit the virus to others.”
Madhi is Dean of the Faculty of Health Sciences and Professor of Vaccinology at the University of the Witwatersrand.
The critical point, however, is that while a vaccinated person may have the same viral loads as an unvaccinated person, the duration of viral shedding (when a virus is released from the infected host) and the type of symptoms that the vaccinated individual displays are much less than in unvaccinated individuals, he said. This has been seen with both the J&J and Pfizer-BioNTech vaccines.
“So you might start off with the same viral load, but the duration of shedding of the virus and the actual symptoms that result in breakthrough infections is much, much less compared to unvaccinated individuals,” said Madhi.
One of the reasons for this much more rapid decline of the viral load in vaccinated individuals is that the infection induces memory responses in the immune system, which, in turn, quickly brings about antibody responses that limit the further replication of the virus by clearing it.
Data from the UK based on breakthrough infections in healthcare workers also showed that they were less likely to transmit the virus to members in a household, likely due to them having a more rapid clearance of the virus, said Madhi.
A Chinese study also found that breakthrough infections with the Delta variant showed that people were 2.84 times less likely to infect household members.
Natural infection vs vaccination: immunity
Immunity from natural infection does offer good protection against reinfection, but it does not work better than vaccine-induced immunity, said Madhi.
“When it comes to protecting against severe disease, natural infection works extremely well. But natural infection induces a much less robust antibody response. And, in fact, a less predictable antibody response that is induced by vaccines was shown in the Novavax study in SA. So natural protection does not have better protection, or even similar protection, compared to vaccine-induced immunity,” he said.
Herd immunity unlikely
Herd (population) immunity refers to adequate immunity at the population level, which brings about a complete interruption in the chain of transmission of the virus.
While some experts believe it is still achievable, Madhi said that it’s unlikely we would reach it, especially with the Delta variant circulating.
“With the Delta variant, we would need to get 85% of the population protected against infection … none of the vaccines currently come close to being able to provide [very high] protection against infection and mild disease, including the Pfizer vaccine,” said Madhi.
“So even if we were to vaccinate 40 million or 60 million South Africans tomorrow, we are not going to get herd immunity because we don’t have the right tools. But that doesn’t mean that getting even some level of interruption of transmission of the virus with the vaccines, is not of massive public health importance,” he added.
Herd immunity was never the goal of the vaccines – the goal was for it to protect against severe disease, hospitalisation and death, which it has proven to do quite successfully.
“The whole issue of herd immunity is something that we shouldn’t really be discussing. We certainly shouldn’t be trying to convince the public that we’re trying to get to herd immunity – we will disappoint the public and lose further credibility by promising something that is not going to materialise anywhere in the world, including in Israel, where they’re going for their third dose of the vaccine,” said Madhi.
The UK has set out plans to end social and economic Covid restrictions, with British health minister Sajid Javid recently stating that he did not expect the country to see any more lockdowns.
“The reason why they could get back to a normal lifestyle is not by chasing herd immunity,” said Madhi. Instead, they recognised that they would have resurgences and breakthrough infections, but aimed to get to a place where they could attenuate the magnitude of the resurgence, which is what the vaccines are doing for the Delta variant in the UK, he said.
“It protects extremely well against severe disease and death. So we’re not looking at trying to get rid of Covid – it’s not going to materialise with the current vaccines, even if we vaccinate 100% of the population,” said Madhi.
“The bottom line is that if you are unvaccinated, you’re 50% – 75% more likely to infect other people than if you are vaccinated. And that in itself should be a compelling reason why people need to take responsibility for their inaction of not being vaccinated,” said Madhi.
While an individual may have the right to choose not to be vaccinated, they are putting the broader population at risk of infection, and it needs to come with consequences, he added.
“And the type of consequences it needs to come with is pretty much what the evidence is suggesting – vaccine passports, which require you to go through different steps compared to a vaccinated person, and you have to make use of certain facilities. And that is the right thing to do,” said Madhi.