AS A growing body of data suggests that vaccine-induced protection from covid-19 declines over time, many nations are gearing up to roll out a booster programme. Israel has already begun, while the US, France and Germany have all announced plans to begin rolling out third doses. Some other countries, including the UK, are holding back, with results from a key trial of third shots expected imminently.
The Joint Committee on Vaccination and Immunisation, which advises UK health departments, has been mulling over booster shots for some time. In June, it issued , starting with care home residents, front-line healthcare and social care workers, people aged over 70 and adults who are clinically extremely vulnerable or immunosuppressed. But this is largely yet to materialise: all that has been announced so far is a limited programme of third shots for people who have severely weakened immune systems.
Declining protection
There has been speculation since early in the development of the coronavirus vaccines that booster doses would be needed, perhaps to combat newer variants. But time is also a factor. For many diseases, the strength of the immune response – stemming from either natural infections or vaccines – wanes over time periods ranging from months to years.
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Several studies have shown that, as expected, antibody levels fall gradually in the months after coronavirus vaccination. Antibodies aren’t the whole story, as the memory cells that make antibodies and other immune cells called T-cells can persist in various sites in the body, ready to spring into action if needed, but it is much harder to detect these in people via tests.
However, we can measure how well vaccines are working in practice at stopping people from getting ill. Studies of covid-19 vaccination have given varying estimates of this. Recent Israeli data caused concern when it showed a person’s protection from infection could be as low as 40 per cent roughly six months after the nation’s vaccination programme began, although protection against severe disease seemed to be holding up, .
Last month, , from 93 per cent two weeks after a second Pfizer/BioNTech dose to 71 per cent three months later. After two Oxford/AstraZeneca jabs, the figures were 72 and 61 per cent respectively.
Findings such as these are why some countries have begun offering third doses. In July, Israel became the first country to start providing boosters, to those aged 60 and over who had their second shot five months ago or earlier. Last week, this was extended to all adults and teenagers.
Results from the first people in Israel to get boosters show these work well at preventing both severe disease and milder infections. From 12 days after the third dose, the number of infections fell at least fivefold compared with people who’d had two jabs. “Our findings give clear indications of the effectiveness of a booster dose even against the delta variant,” said .
“If it becomes a fact that we need three doses, then vaccine equality is going to suffer”
Critics say the UK is an outlier for not having a booster programme in place by now. The UK government says the third shots now on offer to people with weak immune systems , but “top-up” doses, to remedy the fact that two jabs don’t seem to work fully in these people.
But the UK isn’t alone: Spain, Denmark and the Netherlands have taken a similar stance. The European Centre for Disease Prevention and Control .
Offering boosters so soon after the first two jabs raises the question of how often they will be needed, says . “We need to consider the effects of repeated immunisations – what side effects will that have? We haven’t studied having third, fourth, fifth doses yet.”
Global disparities
Another argument against boosting is that it is unfair to low-income countries, many of which haven’t yet been able to give a first dose to most of their vulnerable groups. It is like giving extra life jackets to people already wearing them while others drown, said Michael Ryan at the World Health Organization last month.
“If we had a limitless supply of vaccines, I would say do it, but we don’t,” says , UK. “If it becomes a fact that we need three doses, then vaccine equality is going to suffer.”
When 91av went to press, results were expected imminently from a key trial called .
This will provide more information about whether it is advisable to “mix and match” the vaccine brands, which could provoke a stronger immune response based on past experience with other diseases. The UK programme offering a third vaccine to people with very weak immune systems will see the Pfizer/BioNTech or Moderna shots given to many people who previously had Oxford/AstraZeneca jabs. Israel, however, has been offering a third dose of the Pfizer/BioNTech vaccine to people who have already had two, and the US looks set to do the same.
