UK and Russian scientists are to test whether combining shots of the Oxford/AstraZeneca and Sputnik V coronavirus vaccines could result in better protection than two doses of the same one.

Trials will start by the end of the year, the Russian Direct Investment Fund (RDIF), which funded the development of the Sputnik V vaccine by Russias Gamaleya Institute, said on Friday. AstraZeneca confirmed that it was considering how it could assess combinations of different vaccines, and would soon begin exploring with the Gamaleya Institute whether their two vaccines could be successfully combined.

Like the Oxford/AstraZeneca vaccine, the Russian Sputnik V shot is based on a modified version of adenovirus, a common cold virus. This vector is stripped of any disease-causing genes and modified to carry genetic instructions for making the coronavirus spike protein, which it passes to human cells. The manufactured coronavirus spike protein then triggers an immune response that protects against the Covid-19 disease.

A potential problem with such vaccines, however, is that of anti-vector immunity, where if the immune system has previously encountered the type of adenovirus used in the vaccine, it may destroy it before the vaccine can trigger an immune response. This is why the Oxford University group chose to use a chimp adenovirus, rather than a human one. However, anti-vector immunity could also reduce the efficacy of booster shots, if this involves injecting the same virus for a second or third time.

Mixing and matching different vaccines may provide a solution. This concept is known as a heterologous prime-boost, and has been used in vaccination programmes against other diseases.

Now that the UK has authorised the first Covid vaccine, who will get it first?

The governments Joint Committee on Vaccination and Immunisation (JCVI) says its priority is to prevent Covid-related deaths and protect health and social care staff and systems.

Elderly care home residents and their carers are first on the JCVIs list because their risk of exposure to the virus is higher and because the risk of death closely correlates with older age. They are followed in priority by anyone else over 80 and frontline health and social care workers.

Even so, for pragmatic reasons NHS staff are likely to be the first group to receive the Pfizer/BioNTech jab. This is because the vaccine needs to be stored at ultra-cold temperatures, which can be achieved more easily by using hospital facilities

Are there enough doses to reach all the priority groups?

Together, care home residents, their carers and the over-80s make up nearly 6 million people, and frontline NHS staff a further 736,685. Matt Hancock, the health secretary, has said he expects 10m doses of the Pfizer/BioNTech vaccine to be available this year, so if this is the only vaccine authorised, everyone else would have to wait until further doses become available next year.

Where will I go for the vaccine?

Covid-19 vaccines are expected to be delivered at three types of venue: NHS trust vaccine hubs at hospital sites; mass vaccination centres, which are in the process of being set up at places such asfootball stadiums, conference buildingsand racecourses these are expected to vaccinate up to 5,000 people a day; and at GP surgeries and pharmacies. GPs can also visit care home residents and housebound patients at home without them needing to travel.

How far apart will the two doses be administered, and will I protected after the first?

While there is some evidence to indicate high levels of short-term protection from a single dose of vaccine, a two-dose schedule is what has been approved by theMHRA.

The second dose will need to be delivered at least 21 days after the first, and both will be injected into the deltoid muscle the thick triangular muscle we use to raise each arm.

For the Pfizer vaccine, its efficacy rate was calculated seven days after the second shot. It is likely that people will have some protection before this, but this is how long it will take for full protection to kick in. We will learn more about the extent of protection and how long it lasts as data from ongoing clinical trials comes in.

Can I pay to get the vaccine privately?

Unlikely. Englands deputy chief medical officer, Jonathan Van-Tam, has said he believes Covid-19 vaccines should be delivered according to clinical priority rather than allowing people to jump the queue if they can afford it.

Will I be able to choose which vaccine I have?

Also unlikely, at least in the short to medium term. Assuming more than one vaccine is approved, the priority will be distributing any available doses to the people who need it as quickly as possible.

Linda Geddes

Unlike AstraZenecas vaccine, Sputnik V uses two different human adenovirus vectors to try to trigger a stronger and longer-term immune response. It is not yet clear which of these components will be tested alongside the AstraZeneca vaccine.

Anti-vector immunity could also provide a possible explanation of why the AstraZeneca vaccine appears to work better when given as a half-dose followed by a full one, rather than two full doses.

Earlier this week, the outgoing chair of the UKs vaccine taskforce, Kate Bingham, announced that a trial of AstraZenecas vaccine in combination with the Pfizer shot was likely to begin in January. Its to do with trying to trigger the immune response and the durability [of the response], she said.

RDIF said it approached AstraZeneca about the possibility of combining its vaccines on 23 November.

This could eventually extend the duration of immunity and possibly also protect against people receiving the same vector repeatedly and having a less robust response, said Beate Kampmann, the director of the vaccine centre at the London School of Hygiene & Tropical Medicine. But for now these are all theoretical concepts that need to be carefully tested before they can be extended to population use.

Russia is likely to see the move as a vote of confidence by a western manufacturer in Sputnik V, which is already being used to immunise medical workers, teachers and social workers. Russian officials previously announced that the vaccine had more than 95% efficacy, giving it a success rate comparable to vaccines being developed by Pfizer and Moderna.

The decision by AstraZeneca to carry out clinical trials using one of two vectors of Sputnik V in order to increase its own vaccines efficacy is an important step towards uniting efforts in the fight against the pandemic, said Kirill Dmitriev, chief executive of RDIF. We hope that other vaccine producers will follow our example.

Dr Stephen Griffin, associate professor in the school of medicine, University of Leeds, said: The importance of a second jab should not be underestimated as it is important for the longevity, specificity and effectiveness of the response to most vaccines.

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Oxford Covid vaccine to be combined with Sputnik jab for trial - The Guardian