By Michael Gwarisa
Data from a new study that sought to examine vaccine effectiveness in light of circulating Coronavirus variants following vaccination, has shown that the effectiveness of vaccines that were widely administered in Zimbabwe between 2021 and 2022 has weakened against emerging COVID-19 variants.
The study dubbed COVID-19 vaccine effectiveness and SARS CoV-2 variants in Zimbabwe: Test Negative Case-Control study, Genetic sequencing and Serology (ZIMCoVVAR) was a test-negative case-control study to evaluate the effectiveness of inactivated vaccines and was conducted from November 2022 to October 2023. The study did not administer vaccines but enrolled individuals vaccinated with vaccines like Sinopharm and Sinovac. The vaccines were based on the original Wuhan virus strain.
In an interview with HealthTimes on the side-lines of the results dissemination meeting in Harare, Dr Tariro Makadzange, the Principal Investigator of the ZIMoVVAR study and the director of Mutala Trust said the adoption of annual vaccination strategies may be needed in Zimbabwe to prevent the population against infection and severe COVID-19 should more virulent strains emerge.
So I think even that vaccine effectiveness estimate is a combination of vaccine and natural infection as well. In addition, when we break down whether you were vaccinated a year ago or more than a year ago, the closer you are to vaccination, the better the vaccine effectiveness. Effectiveness diminished with time from the first variant that is the Wuhan one up to the last one,” said Dr Makadzange.
“So in general with Omicron, people do very well. It’s not as severe as some of the earlier strains of the virus were. And then for you as an individual, the further you are from the vaccination, the less effective it’s going to be. And that’s why in some places they’re recommending annual vaccines, right? So, you know, if you’re in the United States, for example, you get your annual influenza and COVID vaccine at the same time. And that’s why they’ve made vaccines that are Omicron specific as well.”
Zimbabwe used the Sinopharm Sinovac COVID-19 vaccines that were designed with the original Wuhan strain. However, other variants have been emerging ever since.
“COVID has not been static, right? It’s been evolving. And so one of the things we wanted to understand is what that evolution has been, and then how that evolution impacts the vaccine effectiveness. So the evolution has been there, you know from Alpha, Beta, Delta, then at the end of 2021, there was Omicron. And so we wanted to know how effective these vaccines are in the setting of evolving viral variants. So to do that, we needed to also understand two other things. And so you see that in the title of our study.”
The study enrolled over 5,000 participants, including more than 4,400 COVID PCR negative controls and 700 COVID PCR positive cases all presenting with symptomatic disease based on WHO criteria for COVID-like illness. Participants were enrolled across 21 sites including central hospitals, provincial hospitals, and clinics in seven provinces. Approximately two-thirds were enrolled at hospital sites. This comprehensive study included genotyping to define the circulating variants and serological evaluation to evaluate the role that natural infection-induced immunity can have on Vaccine Effectiveness (VE).
“So the study is a COVID vaccine effectiveness study. So what does that mean? So efficacy is typically defined in the clinical trial, but effectiveness gives you a sense in the real world, in the public, how a drug or vaccine works etc. So this is the vaccine effectiveness study for the inactivated vaccine. The reason that it’s important is there aren’t that many studies in Africa, unfortunately.”
WHO data suggests that there are approximately 551 vaccine studies and only about 11, 9 are from Africa. Many of those are in South Africa and many are mRNA adenovirus, but nothing on the inactivated like the Sinopharm, Sinopharm that Africa used.
“And about 20 percent of Africans who were vaccinated were vaccinated with an inactivated vaccine. So our funder put out a call for proposals to study vaccine effectiveness, specifically with inactivated vaccines because this gap in data existed. It was competitively applied and we were fortunate to be successful. And so we launched the study,” added Dr Makadzange.
The study aimed mainly to explore two objectives with the first one being to look at the sequences of the isolates of COVID from the people who tested positive. The other objective was to understand how much natural immunity is also contributing.
“So if you’re in a vacuum, you get vaccinated, the only thing that protects you from the virus or pathogen is that vaccination. But when you live out in the real world, you’re also getting exposed to viruses. So you have the vaccine-inducing immunity, but you also have all these viruses that you’re seeing and what kind of immunity are those viruses inducing? So we wanted to know, do people have antibody responses already, and if so, how is that impacting the vaccine effectiveness?”
COVID-19 infection was seasonal peaking between Jan-March and Jun-Aug. The study recorded a high seropositivity rate of 92% against the Wuhan strain, indicating widespread natural infection-induced immunity. The dominant circulating variants were Omicron variants identified by sequencing. The XBB.1.5 and its subvariants such as XBB.1.5.28 were the dominant circulating variants during the study period. Disease severity had significantly waned during the study period. Among study participants, there were 13 deaths, 11 in cases.
The number of deaths was small however notable that uncontrolled HIV was associated with an increased risk of death. Vaccine effectiveness (VE) stood at approximately 20% against symptomatic disease. This effectiveness was notably higher within the first year following vaccination. The observed VE is attributable to the presence of Omicron variants, which are significantly mutationally different from the original Wuhan strain and are not covered by the vaccine in use, high population seroprevalence suggesting significant rates of natural infection, and decreased disease severity from the current circulating variants. Analysis and model refinement is ongoing.
“So if I were to make a policy recommendation, what I would say is vaccination is absolutely good. It can be very, very helpful. Probably you need to be vaccinated within a year. And we saw that people who were boosted had much better vaccine effectiveness than people who weren’t boosted. We also saw that you know you probably need to target the circulating strains. It’s hard to use the Wuhan vaccine for the Omicron strains so you probably need to develop vaccines for new strains,” added Dr Makadzange.
