As the world continues to battle the COVID-19 pandemic amid the spread of the highly contagious Delta variant, several governments are preparing vaccine booster drives.
Countries including Israel, the United Kingdom and the United States, which have already vaccinated a substantial share of their populations, have started or announced programmes to offer fully vaccinated people an extra dose of vaccine in an attempt to increase their populations’ protection against COVID-19.
Israel, which has mainly used the Pfizer-BioNTech vaccine in its rollout, started offering booster doses in July to people over 60 years old in response to an uptick in cases. In late August, the government made booster shots available to anyone at least five months after their second jab.
Israel so far has administered more than two million booster shots, and the government has said it is preparing to ensure it has sufficient supplies in case a fourth dose is needed.
Germany and France also started offering an additional shot to some fully vaccinated people this month, beginning with the most vulnerable groups. The United Kingdom will this month offer booster shots to anyone over 50, front-line health workers or the clinically vulnerable.
Meanwhile, the US said in August it hoped to offer booster vaccines from September 20 to those who had received the Moderna or Pfizer shot at least eight months previously, if both the US Food and Drug Administration (FDA) and the US Centers for Disease Control and Prevention (CDC) agree.
The country currently offers an extra shot to those with weakened immune systems. The FDA and the CDC are expected to offer recommendations on the wider use of booster shots within days.
But several scientists, NGOs and the United Nations health agency have rejected rich countries’ plans to offer booster doses to younger, healthy people.
The World Health Organization (WHO) has called for a moratorium on booster shots at least until the end of the year, arguing that limited vaccine supplies should be allocated to low-income countries with low vaccination rates before high-income countries offer their populations additional doses, because it would save more lives.
Some scientists have cautioned that the immunological case for booster shots is not strong enough, due to a lack of evidence regarding vaccine effectiveness over time.
Here are the key questions around booster shots:
What is a booster shot and what is a third dose?
According to the US CDC a booster dose is understood as an additional dose given to a person that has already received the two doses of the vaccine and built enough immunity protection, but whose protection has decreased over time. The booster shot is designed to prolong immunity.
The term third dose or third shot has been used for cases where an individual’s immune system has not fully responded to the first two shots of vaccine. According to the CDC, people who are moderately to severely immunocompromised will get a third dose rather than a booster.
Dr Jeffrey Lazarus, Head of the Health Systems Research Group at ISGlobal Barcelona Institute for Global Health, said there needs to be “clarity on the language” when discussing booster shots and third doses.
“Right now, two doses of the vaccines … are not having the needed antibodies response. So therefore some people are calling it a booster, and some are saying simply that it turns out [that] in the real world when using the vaccine we need three doses to produce the needed response,” he said.
“So some people are calling it a three-dose vaccine for a certain population,” he added.
Several countries have announced or launched programmes administrating third doses to vulnerable groups, including immunocompromised individuals.
Is protection from vaccines falling?
It is common for the protection from vaccines to wane with time and booster shots are typically used to increase antibody levels for longer.
Several studies into so-called breakthrough infections in the US have suggested there is a reduction in vaccine effectiveness against infection over time.
However, the studies have also suggested that there were no major increases in hospitalisation or death rates over time among fully vaccinated people.
Several studies around the world have shown that the vaccines are extremely effective in preventing severe cases of COVID-19 and are even more effective at preventing hospitalisation and death among fully vaccinated people.
New data released by Moderna this week suggested that the protection given by its COVID vaccine wanes over time. The company’s analysis, which was yet to be peer reviewed, found higher rates of infection among groups who were vaccinated more than one year ago compared with those who were vaccinated eight months ago.
Pfizer has said data from its own early clinical trials suggested that vaccine efficacy declines after participants received their second dose and that a booster shot was safe and helped to restore antibody levels.
In July, UCL Virus Watch found that antibodies generated by the Pfizer-BioNTech and the Oxford-AstraZeneca COVID vaccines started to decline as early as six weeks after full vaccination.
The WHO has said it is not clear if studies showing levels of antibodies falling over time means a reduction in vaccine effectiveness.
The European Medicines Agency and the European Centre for Disease Prevention and Control have said that based on current evidence, there is “no need” for the administration of booster shots in the general population.
Several international scientists wrote in The Lancet medical journal that booster shots “are not appropriate at this point in the pandemic” for healthy and younger people in the US, citing a lack of evidence about waning protection among younger these groups.
“The currently available studies do not provide credible evidence of substantially declining protection against severe disease, which is the primary goal of vaccination,” said lead author Ana-Maria Henao-Restrepo, of the WHO.
While the antibodies produced by the vaccines play a key role in preventing infection, some experts have stressed that the shots have also generated other immune defences in the form of B and T cells, which can prevent severe illness.
“Antibodies are the first line of defence,” Dr Roselyn Lemus-Martin, who holds a PhD in molecular and cell biology from the University of Oxford, told Al Jazeera.
“[But] there are also B and T cells and those cells generate a cellular immunity which lasts for years,” she said.
According to Lemus-Martin, those cells also help generate an immune response that will help prevent severe illness or death.
“The issue is that we are focusing on the antibodies because is what we can measure, we won’t be measuring the cells … so in a way, we are using the boosters to protect ourselves from the symptoms but not from a serious disease or death,” she added.
Are booster shots a good use of limited vaccine supplies?
Scientists have largely backed rich countries’ plans to offer third doses to immunocompromised people and other at-risk groups.
But several scientists, NGOs and the WHO have warned rich countries against offering booster jabs to younger, healthier groups, arguing that limited vaccine supplies would save more lives if allocated to vulnerable groups in lower-income countries which have yet to be fully vaccinated.
“The best way right now is to provide a booster to those who are immune-suppressed and then to ensure that all available vaccines go to countries that need them and go to the priority populations in those countries, which are the elderly and the first-line health care workers,” Lazarus said.
Others have noted that it is imperative to boost immunity in populations with weak vaccine coverage to reduce the chance of new virus variants emerging.
“The argument of many pharmaceuticals is the new strains are reducing our antibodies through time, but many of us argue that we don’t need this boost so early,” Lemus-Martin said.
“In reality what we need is to start vaccinating the people around the world … so we can prevent the emergence of new strains,” she added.
Why is there a disparity in vaccination rates?
The WHO has set a target for every country to fully vaccinate at least 10 percent of its population by the end of this month, at least 40 percent by the end of this year and 70 percent by the middle of next year.
But the UN health agency said in early September that of the 5.5 billion coronavirus vaccines administered at the time, 80 percent were assigned to upper and middle-income countries.
Experts have said a key reason behind the disparity is that vaccine production is limited and that supplies are not being distributed fairly.
According to Dr Bruce Aylward, a senior adviser to the WHO, the scarcity of supplies available to lower-income countries is a consequence of rich countries striking deals with the vaccine manufacturers to secure much of their short-term production capacity.
“Right now, if you look at how vaccines are being used globally, the uptake rate by high-income countries, upper-middle-income countries, is absorbing too much of the global supply for the lowest-income countries,” Aylward said last month.
In a recent interview, Mamta Murthi, the World Bank’s vice president for human development, called for more transparency around “how many doses can be manufactured, who are these committed to, where are the surplus doses so that we can have reallocation towards countries that need those doses”.
The head of Pfizer, Albert Bourla, has rejected arguments that the company’s plan for booster shots in the US would divert doses dedicated to low and middle-income countries.
“The introduction of booster doses should not change the number of doses that each country receives,” he wrote in an open letter published on Thursday, adding that none of the company’s commitments to any country would change if booster shots were approved in the US.
Meanwhile, several charities and NGOs have urged pharmaceutical companies that produce vaccines to waive intellectual property rights and share their know-how with manufacturers in poorer countries, to allow them to produce generic copies of the vaccines and boost global supplies.
“Rich countries need to stop blocking the ability of developing countries to be able to produce their own vaccines,” Max Lawson, head of inequality policy at Oxfam, told Al Jazeera.
“We have a situation where a few pharmaceutical firms have a monopoly of these successful vaccines, and they are failing to share their technology … So, a booster that is given to an elderly person in Israel is a vaccine that has been taken away from a person in South Africa.
“The only reason we have that is because of the artificial scarcity created when you have a monopoly, and you have only a few companies that are licensed to be able to produce these vaccines,” Lawson added.
Will vaccine supplies increase soon?
The International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) Director General Thomas Cueni said earlier this month that pharmaceutical companies are now producing some 1.5 billion doses of vaccine each month and that rich countries building stockpiles “no longer need to do so”.
The IFPMA said projections showed that 12 billion doses could be available by the end of the year, and 24 billion by June 2022.
Modelling produced by data analytics company Airfinity shows that wealthy countries could vaccinate their populations, including offering boosters to at-risk populations, and have around 1.2 billion extra doses that could be redistributed by the end of the year.
Meanwhile, several rich countries have already pledged to donate one billion doses to lower-income countries, but fewer than 15 percent of those have materialised, WHO Director-General Tedros Adhanom Ghebreyesus said last week.
“We don’t want any more promises. We just want the vaccines,” he said, repeating a call for a moratorium on booster shots.
“I’m calling for an extension of the moratorium until at least the end of the year to enable every country to vaccinate at least 40 percent of its population,” he said.