Two doses of the Pfizer/BioNTech vaccine seems to provide better protection initially against the Delta variant of Covid-19 when compared to the Oxford/AstraZeneca jab, but its efficacy declines faster, early research suggests.
Scientists from Oxford University have said that after four to five months, the level of protection offered by both vaccines is similar, with the AstraZeneca jab maintaining its effectiveness throughout the duration.
Independent experts said the findings, which have not yet been peer-reviewed, support the case for third “booster” jabs for vulnerable individuals.
The researchers said that although jabs did not eliminate the chance of getting Covid-19, they did reduce the risk and remained the most effective way to ensure protection against the Delta variant, which has become dominant in the UK.
Dr Koen Pouwels, senior researcher at the University of Oxford’s Nuffield Department of Population Health, said that the team “can be confident” that the numbers “really represent a decline” for the Pfizer vaccine, whereas for AstraZeneca there was essentially “no change at all in the protection from AZ”.
But he said: “Even with these slight declines in protection against all infections and infections with high viral burden, it’s important to note that overall effectiveness is still very high because we were starting at such a high level of protection.
“It is also worth highlighting that these data here do not tell us about protection levels against severe disease and hospitalisation, which are two very important factors when looking at how well the vaccines are working.”
Autumn booster campaign
NHS officials have geared up to start offering a third coronavirus jab from early September, but are yet to be given the go-ahead from the Joint Committee on Vaccination and Immunisation (JCVI).
A bigger flu season than normal is expected, meaning extra protection against Covid is likely to be needed.
More than 30 million of the most vulnerable should receive a third dose, vaccine experts are advising. They will include all adults aged 50 and over, and anyone over 16 who qualifies for a flu jab.
The Oxford University academics said they could not comment on what the new study might mean for the potential autumn booster campaign, but said that the JCVI would be considering the data while making its decision.
Interim advice from the JCVI is that boosters will help maintain protection against Covid-19 and new variants for those most at risk, before winter comes.
The vaccines are thought to protect most people against serious illness for at least six months, but a lack of data on exactly how long immunity lasts is prompting a safety-first approach.
The JCVI will deliver guidance before the programme is due to commence on September 6.
Ministers are understood to be waiting for further results from the Cov-Boost trial – led by University Hospital Southampton NHS foundation trust and backed by £19.3m of government funding through the Vaccines Taskforce – to see which vaccines should be used in the autumn programme.
The study will trial seven vaccines and will be the first in the world to provide vital data on the impact of a third dose on patients’ immune responses.
The study also suggested that the time between doses did not affect effectiveness in preventing new infections, and that younger people (aged 18-34) had more protection from vaccination than older age groups (35 to 64-year-olds).
Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said: “The Pfizer jab provided greater initial protection than the AstraZeneca one, but then after around five months the level of immunity dropped to about the same level seen for both of the vaccines looked at.
“On this evidence, it certainly supports the case for third ‘booster’ jabs for vulnerable individuals, as is now happening in Israel.
“Moreover, these datasets scotch claims that protection provided by the UK’s vaccination programme is likely to be superior to Israel’s because of our longer window between first and second doses.”
People who had been vaccinated after already being infected with Covid had even more protection than vaccinated individuals who had not had the virus before, the study found.
The scientists also found that a single dose of the Moderna vaccine had similar or greater effectiveness against the Delta variant as single doses of the other vaccines. However, the researchers added that they did not yet have any data on second doses of the US-made jab.
Sarah Walker, professor of medical statistics and epidemiology at Oxford University, said: “We don’t yet know how much transmission can happen from people who get Covid-19 after being vaccinated – for example, they may have high levels of virus for shorter periods of time.
“But the fact that they can have high levels of virus suggests that people who aren’t yet vaccinated may not be as protected from the Delta variant as we hoped. This means it is essential for as many people as possible to get vaccinated – both in the UK and worldwide.”
The study was conducted in partnership with the Office of National Statistics and the Department for Health and Social Care.
