Scientists have reacted with scepticism to claims by AstraZeneca’s CEO that low uptake of the Oxford/AstraZeneca jab among elderly Europeans could explain the current surge in Covid-19 infections in mainland Europe.
Pascal Soriot told BBC Radio 4’s Today programme that differences in T-cell immunity between the vaccines might mean that those who received the Oxford/AstraZeneca jab had longer-lasting immune protection against the virus. T- cells are a class of immune cells that educate antibody-producing B cells about the nature of the viral threat and directly kill infected cells.
Soriot said: “It’s really interesting when you look at the UK. There was a big peak of infections but not so many hospitalisations relative to Europe. In the UK [the Oxford/AstraZeneca] vaccine was used to vaccinate older people whereas in Europe people thought initially the vaccine doesn’t work in older people.
“What I’m saying is that T-cells do matter and in particular it relates to the durability of the response, especially in older people, and this vaccine has been shown to stimulate T-cells to a higher degree in older people. There’s no proof of anything … we don’t know. But we need more data to analyse this and get the answer.”
Germany was the first European country to recommend not giving the AstraZeneca jab to people over 65 in late January, citing a lack of efficacy data for the vaccine in this age group. Other European countries swiftly followed with similar recommendations, including Italy, France, Poland and Sweden, although many later reversed this guidance after the publication of further efficacy data.
Some eventually even said it should only be used in older age groups, after the European Medicines Agency (EMA) reported a possible link between the vaccine and very rare cases of blood clots. Possibly as a result of these mixed messages, many Europeans were initially reluctant to receive the jab.
There are theoretical reasons why the AstraZeneca vaccine might trigger slightly different immune responses compared with an mRNA-based vaccine such as the Pfizer jab. Both equip cells with the genetic instructions to make the coronavirus spike protein, but the AstraZeneca vaccine does so with the help of a modified virus, which the immune system might also be responding to.
Deborah Dunn-Walters, the chair of the British Society for Immunology’s Covid-19 taskforce and a professor of immunology at the University of Surrey, said: “It’s a slightly more complicated delivery system, so you might expect there to be differences – but trying to explain those differences would take a lot of research.”
Getting jabs to the unvaccinated has never been more critical
Danny Altmann, a professor of immunology at Imperial College London, said it would be “foolhardy” to try to attribute the differences in the shape of individual countries’ infection curves to any single factor. “I don’t know where you’d start to do that scientifically,” he said. “All of the vaccines are, to varying degrees, pretty amazing. They all induce the full gamut of immunity, including neutralising antibodies and [different types of] T-cells.”
Prof Matthew Snape, of the University of Oxford, has compared antibody and T-cell responses in people receiving standard or mixed schedules of the Pfizer and AstraZeneca vaccines. Although his team found evidence that a single dose of AstraZeneca induced a better T-cell response, the response was very similar shortly after receiving two doses. “Intriguingly, the best T-cell responses seem to come if you give a first dose of the AstraZeneca vaccine followed by Pfizer,” he said.
Finding ways to optimise the immune response to Covid-19 vaccines is an ongoing focus of research, and Snape is following up these studies to see how people’s immune responses shape up in the longer term.
Understanding the differences between countries’ infection and hospitalisation rates is further complicated by factors such as when Covid-19 restrictions were lifted and to what degree, variability in the gap between first and second doses, the age of the population and the prevalence of other diseases, and the appearance of new variants, especially if they appear a long time after people have been vaccinated.
“Drawing comparisons between countries presents many difficulties and is very likely to lead to conclusions which are not reliable,” said Dr Lance Turtle, a senior clinical lecturer and consultant physician in infectious diseases at the University of Liverpool.
Earlier a former chair of the UK vaccine taskforce, Dame Kate Bingham, urged the government to do better in its preparation for future disease outbreaks. Writing in the Times, she said the machinery of Whitehall was “dominated by process rather than outcome, causing delay and inertia”, adding that the jab rollout would have been delayed if it had been left to the normal workings of government.
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