Scared by fresh surges that the Delta variant of the novel coronavirus is fuelling around the world and in light of findings that vaccines may be less effective against it, many countries across the world are lining up booster shots for people to augment the protections offered by the general course of inoculation. Health experts, especially WHO, have urged that plans for booster shots can wait while many of the poorer countries are still struggling to find vaccines for their populations. Now, a paper published in respected medical journal Lancet has said that “current evidence does not… appear to show a need for boosting in the general population, in which efficacy against severe disease remains high".
What Are The Risks With Boosters Highlighted By The Experts?
The Lancet paper, ‘Considerations in boosting Covid-19 vaccine immune responses’ — it counts among its authors the World Health Organisation (WHO) Chief Scientist Dr Soumya Swaminathan — says that while booster shots may seem like an attractive option for enhancing waning immunity, any decision on their rollout has to be based on solid evidence.
“Although the idea of further reducing the number of Covid-19 cases by enhancing immunity in vaccinated people is appealing, any decision to do so should be evidence-based and consider the benefits and risks for individuals and society," it said, adding that “widespread boosting should be undertaken only if there is clear evidence that it is appropriate".
The paper underscores the importance of “primary Covid-19 vaccination", which it says “clearly outweigh(s) the risks", but points to risks from boosters if they are widely introduced, or given too frequently, especially when vaccines “that can have immune-mediated side-effects". The paper notes that cases of myocarditis and Guillain-Barre syndrome have been reported following vaccination by mRNA shots (particularly after the second dose) and adenovirus-vectored Covid-19 vaccines, respectively.
Why Full Vaccination Is Being Said To Be Good Enough, For Now?
While there are frequent reports of studies showing that the vaccines currently being used are demonstrating lower efficacy against the later variants of the novel coronavirus, the experts said that “most of the
observational studies on which this conclusion is based are, however, preliminary and difficult to interpret
precisely due to potential confounding and selective reporting".
Instead, they point to a “consistent finding… that vaccine efficacy is substantially greater against severe disease than against any infection". Thus, they say that even though breakthrough cases are reported — that is, of people contracting Covid-19 after receiving their full dose of inoculation — it has been seen that the occurrence of severe infection is low among this group.
“Vaccination appears to be substantially protective against severe disease from all the main viral variants," the paper says. Even when it comes to the more infectious Delta variant, which was first identified in India last year and is now blamed for seeding fresh surges across the world, they point out that efficacy of shots remains reliable.
“Although the efficacy of most vaccines against symptomatic disease is somewhat less for the Delta variant than for the Alpha variant, there is still high vaccine efficacy against both symptomatic and severe disease due to the Delta variant," the paper says.
It also stresses that “to date, none of these studies has provided credible evidence of substantially declining protection against severe disease, even when there appear to be declines over time in vaccine efficacy against symptomatic disease".
So, Are Booster Shots Totally Ruled Out?
No, the experts say that booster shots could be necessary for those in whom the usual course of vaccine doses may be found not to have given rise to adequate immunity.
“Boosting could be appropriate for some individuals in whom the primary vaccination… might not have induced adequate protection — eg, recipients of vaccines with low efficacy or those who are immunocompromised," the paper said. ‘Primary vaccination’ refers to the “original one-dose or two-dose series of each vaccine".
However, one relevant issue suggested by the paper is that if there are some who did not display a satisfactory immune response to primary vaccination, they may not be vastly benefited by an additional shot.
“It is not known whether such immunocompromised individuals would receive more benefit from an additional dose of the same vaccine or of a different vaccine that might complement the primary immune response," they said.
The development of most vaccines now being used had begun in the early days of the pandemic when prior variants were dominant. These early variants have made way for newer variants, which these vaccines were not designed to combat. The Lancet paper points to this gap to suggest that “the effectiveness of boosting against the main variants now circulating and against even newer variants could be greater and longer lived if the booster vaccine antigen is devised to match the main circulating variants".
That is, any boosters should be newly created vaccines that are targeted against the newer variants instead of being just a second or third dose of the same vaccine. The experts say that it is a similar strategy that is used for influenza vaccines, “for which each annual vaccine is based on the most current data about circulating strains, increasing the likelihood that the vaccine will remain effective even if there is further strain evolution".
Can Extra Vaccines Be Put To Better Use?
Although the experts acknowledge that boosters may “ultimately be needed in the general population" because of waning immunity to the primary doses or due to new variants, they emphasise the need to vaccinate as many people around the world as quickly as possible. “Even if boosting were eventually shown to decrease the medium-term risk of serious disease, current vaccine supplies could save more lives if used in previously unvaccinated populations than if used as boosters in vaccinated populations," the experts said.
The rise of breakthrough infections, which is a trigger for countries to plan booster rollout, may not be a reliable indicator of the failure of vaccines to protect against Covid-19, the experts said, since “even without any changes in vaccine efficacy, increasing success in delivering vaccines to large populations will inevitably lead to increasing numbers of breakthrough cases, especially if vaccination leads to behavioural changes in vaccinees".
Reiterating how vaccines provide deeper immunity than what is measured just via antibody levels, the paper said that “protection against severe disease is mediated not only by antibody responses, which might be relatively short lived for some vaccines, but also by memory responses and cell-mediated immunity, which are generally longer
Which Countries Are Going For Boosters?
By now, several of the wealthier countries have already drawn up plans to offer booster shots. While the UK has said it will give a third dose to everyone aged over 50 years and other vulnerable people, the US is looking to bring in a booster dose for people. For now, US authorities plan to give the booster eight months after the first round of vaccination to those jabbed with any of the two mRNA shots — Moderna or Pfizer-BioNTech — that the country is using.
Cyrus Poonawalla, the chairman of the Pune-based Serum Institute of India (SII), which is producing the two-dose Covishield vaccine, was quoted as saying last month that he had taken a third dose of the vaccine along with several employees of the company.
“After six months, the antibodies go down and that is why I have taken the third dose. We have given the third dose to our seven to eight thousand SII employees. For those who have completed the second dose, it is my request to take a booster dose (third dose) after six months," Poonawalla had said.
However, the Lancet paper, pointing to data from Israel — which was the first country to offer booster shots to those aged over 50 years and ones at risk of severe illness, says that it is still early days to conclusively settle for universal booster doses, noting that “a very short-term protective effect would not necessarily imply worthwhile long-term benefit".