- Oxford researchers discovered that their vaccine candidate can prevent COVID-19 transmission in addition to reducing the risk of complications and deaths.
- The scientists also concluded that administering the two vaccine doses 12 weeks apart will increase the efficacy compared to giving the two shots less than 6 weeks apart.
- The Oxford vaccine is available in the UK, Europe, and India, with a Phase 3 trial still ongoing in the US.
We learned long before the first coronavirus vaccine candidates cleared Phase 3 trials that these drugs were not meant to stop the spread of COVID-19. Instead, the vaccines would teach the immune system to react to the virus’s spike protein, so when a person catches COVID-19, the immune system’s defenses are ready to go. The primary goal of vaccines is to reduce the number of severe COVID-19 cases and deaths, not prevent transmission. That would be a welcome side-effect, experts said, but it’s not the main objective of first-generation vaccines. We were told that infection would be possible in vaccinated people. They can also still transmit the illness to others — which is also the case with COVID-19 survivors who can get reinfected and spread the virus to other people, all without even knowing. That’s one reason why safety measures are still necessary for those who have already been immunized against COVID-19.
There has been talk of the Oxford vaccine possibly having the ability to stop transmission, but there wasn’t enough data to support the notion. Moderna execs also speculated that their drug might reduce transmission without having the scientific data to prove it. Almost two months after vaccination campaigns started in the US, UK, Europe, and other countries, the first studies indicate that the vaccines work as intended. They have indeed reduced the number of hospitalizations and deaths. But now, we also have the first study that indicates the Oxford vaccine can prevent transmission — and that the drug can benefit from a big change in the way the two doses are administered.
The AstraZeneca/Oxford vaccine appeared to be the most promising of the frontrunners last fall, but then a series of events lead to trial delays. Once the results were announced, the drug’s efficacy trailed Pfizer/BioNTech and Moderna, and the results themselves drew some criticism for the way they were presented. Furthermore, Oxford’s US study required for emergency authorization has still not been completed, which is why the drug is in use only in the UK, India, and Europe.
But Oxford researchers are continuing the US trial and have penned an additional study showing the drug can prevent COVID-19 transmission. This would give the Oxford drug a notable advantage over vaccines from other pharma companies.
The Oxford vaccine appears to reduce COVID-19 transmission by 67% after the first dose, which would be a great development for the drug. That’s on top of providing protection against complications, including death.
The study was published in pre-print form in The Lancet and has not yet been peer-reviewed.
To measure the risk of COVID-19 transmission in vaccine recipients, the researchers collected nasal swabs. The PCR positivity rate dropped by 67% after the first dose and another 50% after both doses. The PCR positivity would not change if the vaccine had no impact on transmissibility, the researchers argued. More data is required to confirm these findings, and additional studies would be needed to target the new coronavirus strains that are even more infectious than the previous ones.
The initial goal of the study wasn’t to determine whether vaccinated people would stop transmitting the illness. The researchers wanted to determine how a change in vaccination protocol would impact the immune response. The UK was quick to expand the wait time between doses to up to 12 weeks so that more people could receive the first dose. Some have criticized the decision, indicating that it would not respect clinical trial protocols. Current vaccine candidates come with two-dose regimens, involving two jabs given three to four weeks apart, depending on the drug.
Oxford’s new study indicates that coronavirus immunity is attained 22 days after the first jab and lasts for at least 90 days. The vaccine efficacy is 76% after the first shot, the researchers said. They found relatively stable levels of antibodies in volunteers, “with minimal waning by day 90.”
The scientists also found that efficacy rose from 54.9% for an interval between doses of fewer than six weeks to 82.4% for 12 or more weeks between the two vaccine doses.
“These new data provide an important verification of the interim data that was used by more than 25 regulators including the MHRA and EMA to grant the vaccine emergency use authorization,” professor Andrew Pollard said in a statement. ‘It also supports the policy recommendation made by the Joint Committee on Vaccination and Immunization (JCVI) for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected from 22 days after a single dose of the vaccine.”
The authors say the study proves that it’s the dosing interval and not the dosing level that has a greater impact on the efficacy of the COVID-19 vaccine. “This is in line with previous research supporting greater efficacy with longer prime-boost intervals done with other vaccines such as influenza, Ebola, and malaria,” they said.
Despite these findings, other experts warned that more experiments are needed to demonstrate the differences between various dosing schedules. “The study was not designed to look at different dosing gaps or at one versus two doses. This means that participants weren’t randomized and it is therefore quite possible that there are other things that are driving this apparent trend with dosing schedule,” professor Azra Ghani, told UK’s Science Media Centre (SMC), via CNN. Ghani, chair in infectious disease epidemiology at Imperial College London, added that “the only way in which this question can be answered robustly is in a prospective trial with different dosing schedules compared side-by-side.”
One other limitation of the study is that the conclusions apply only to people aged 18-55.
The Oxford press announcement notes that the team will study the efficacy of the vaccine against the new coronavirus variants and that it expects the findings to be “broadly similar” to those reported by other pharma companies. Pfizer/BioNTech and Moderna experiments showed the vaccines are effective against the UK mutation and have some efficacy against the more concerning South African mutation. Phase 3 trial results from Johnson & Johnson and Novavax also proved that efficacy against the South African strain is lower than other variants, but there’s protection against severe cases nonetheless.
