Only high-risk groups should receive ongoing Covid-19 booster doses because strong population-level immunity means ongoing boosting of the general population offers little impact, the latest update from the World Health Organization (WHO) says.
The vaccination guide, from WHO’s Strategic Advisory Group of Experts on Immunisation, says each country needs to take into account its own epidemiological situation, stressing that its recommendations are for short-to-medium term planning and subject to change.
The guide is largely in line with recommendations already in place in Australia, which prioritises high-risk groups.
The “high-priority” group for boosters identified by WHO includes older adults; younger adults with significant co-morbidities such as diabetes and heart disease; people, including children six months and older, with immunocompromising conditions such as HIV and transplant recipients; pregnant people; and frontline health workers.
This high-priority group should get a booster six to 12 months after their last dose, with the timeframe depending on factors such as age and immunocompromising conditions, the guide says.
Healthy adults – usually considered those under the age of 50-60 – and children and adolescents with co-morbidities are considered “medium priority”. The guide recommends one booster dose for this group. While “additional boosters are safe for this group”, they should not be routinely recommended given the comparatively low public health returns, WHO said.
The lowest-priority group is healthy children and adolescents aged six months to 17 years. While primary and booster doses are safe and effective in children and adolescents, the public health impact of vaccinating them is comparatively much lower than the benefits of vaccines to protect them against diseases such as measles.
Some countries have seen concerning disruptions to childhood vaccination programs and a reduction in vaccine rates due to the pandemic, though rates have remained high in Australia.
Prof Julie Leask, a social scientist specialising in immunisation, is currently at a vaccination science meeting in Seoul where she said “we are hearing about the deeply concerning drop in childhood vaccination coverage brought about by the Covid pandemic”.
“Low- and middle-income countries deployed their stretched workforces to delivering Covid vaccines at a cost to childhood vaccination programs,” said Leask, who is with the University of Sydney.
She said globally, those children who had received zero doses of their childhood vaccination schedule in 2021 rose to 18%, or 18.2 million children.
“Now with high levels of Covid immunity and a clearer picture of who is most at risk – the older and those with risk factors – many countries are choosing to re-focus. They are not dropping Covid vaccination altogether, but their workforces are depleted and budgets are stretched, so they need to prioritise according to greatest need.
“We may eventually land on a more stable vaccine booster recommendation in Australia as evidence on longevity of protection against severe disease evolves.”
On Thursday, Australia’s health minister, Mark Butler, announced further measures to protect those most at risk. From 1 April, more than 160,000 people aged 60 to 69 will have free access to the antiviral treatment Paxlovid under expanded eligibility guidelines. The change means people in this age group with only one risk factor for severe illness – instead of two – will get access to the drug, which helps prevent progression to severe illness.
The WHO guide also states “though low overall, the burden of severe Covid-19 in infants under six months is still higher than in children aged six months to five years”.
“Vaccinating pregnant persons – including with an additional dose if more than six months have passed since the last dose – protects both them and the foetus, while helping to reduce the likelihood of hospitalisation of infants for Covid-19.”
Australian Technical Advisory Group on Immunisation (Atagi) guidelines, last updated on 8 February, already emphasise protecting vulnerable people, with increases in protection against severe illness following a booster dose most beneficial for people at higher risk of severe illness.
The only group Atagi recommends receive a booster – regardless of the number of prior doses received – are all adults aged 65 years and over, and adults aged 18-64 years who have medical co-morbidities that increase their risk of severe Covid.
Boosters should be given six months after the last vaccine dose or confirmed Covid-19 infection.
Atagi states adults age 18-to-64 with no risk factors for severe Covid, and children and adolescents aged five-to-17 who have medical co-morbidities or disability with significant health needs may “consider” getting a booster. This is regardless of the number of prior doses received. The advice does not go so far as to routinely recommend a booster for these groups, and states those in these groups need to undergo a risk-benefit assessment with their immunisation provider.
A booster dose is not recommended by Atagi for children and adolescents aged under the age of 18 who do not have any risk factors.
The chair of epidemiology at Deakin University, Prof Catherine Bennett, said the WHO advice is “very much in line with Atagi”.
“Not recommending boosters for younger adults now is not recognition that they don’t work or are too risky as some try to argue, it’s showing that they have worked,” she said.
“We have very high rates of the primary course being taken up, allowing younger populations to transition to hybrid immunity without the more severe disease or even deaths seen pre-vaccination in countries overseas with widespread community transmission.”
More than 1 million Australians have received a booster so far this year, and around seven in 10 of those are aged 60 and over, Butler said.
From 31 March the government will update its reporting of vaccine uptake to report data on how many adults have received a 2023 booster dose; how many have received a dose in the past six months; how many have received one more than six months ago, and how many are completely unvaccinated.
