In a significant announcement, the World Health Organisation said Wednesday that introduction of booster doses should be “firmly evidence-driven” and “targeted” at population groups at highest risk of serious disease, and frontline healthcare workers.
The WHO’s statement on booster doses comes after its Strategic Advisory Group of Experts on Immunisation (SAGE) said evidence till date indicates “a minimal to modest reduction” of vaccine protection against severe disease over six months after the second dose. On October 4, the SAGE had said that introduction of booster doses should be targeted at population groups in greatest need, but it also said it needed to deliberate on evidence for the booster dose.
The WHO recommendations could potentially set the ball rolling for India to look at administration of booster doses to the two priority groups. The interim statement on the booster has significant implications: first, because India closely follows the recommendations of the WHO; and second, India began vaccinating healthcare workers from January 16 this year.
In its interim statement, the SAGE also highlighted that decline in protection against severe disease in high-risk populations calls for targeted use of booster vaccination. “Evidence on waning vaccine effectiveness, in particular a decline in protection against severe disease in high-risk populations, calls for the development of vaccination strategies optimized for prevention of severe disease, including the targeted use of booster vaccination,” it said.
It said that based on a recent systematic review and meta-regression analysis, across the four WHO EUL Covid-19 vaccines that also includes Covishield being administered in India, vaccine effectiveness against severe Covid-19 decreased by about 8% over a period of 6 months in all age groups.
“In adults above 50 years, vaccine effectiveness against severe disease decreased by about 10%. Vaccine effectiveness against symptomatic disease decreased by 32% for those above 50 years of age,” it said.
It said that the duration of protection against the Omicron variant “may be altered and is under active investigation”. “More data will be needed to understand the potential impact of booster vaccination on the duration of protection against severe disease, but also against mild disease, infection, and transmission, particularly in the context of emerging variants,” the WHO said.
It highlighted that the “degree of waning of immunity differs between vaccine products and target populations”. “Circulating viruses -- in particular variants of concern; the extent of prior infection within a community at the time of primary vaccination; the primary vaccination schedule used (i.e. dose interval) and intensity of exposure are all likely to play a role in the findings on waning of protection but cannot be systematically assessed from current studies,” it said.
The WHO reiterated the focus of Covid-19 immunisation efforts “must remain on decreasing death and severe disease, and the protection of the health care system”. It also highlighted that “broad-based administration” of booster doses “risks exacerbating vaccine access... by driving up demand in countries with substantial vaccine coverage and diverting supply while priority populations in some countries, or in subnational settings, have not yet received a primary vaccination series”.
(With inputs from agencies)