Why Covid-19 booster shots are necessary

14 Jan, 2022 - 00:01 0 Views
Why Covid-19 booster shots are necessary Booster doses are administered to a vaccinated population that has completed a primary vaccination series

The ManicaPost

THE World Health Organisation, with the support of the Strategic Advisory Group of Experts (SAGE) on Immunisation and its Covid-19 Vaccines Working Group, continues to review the emerging evidence on the need for and timing of a booster dose for the currently available Covid-19 vaccines.

In recent weeks the SARS-CoV2 Omicron variant has emerged.

 

Data are currently insufficient to assess the impact of this new variant of concern on vaccine effectiveness, in particular against severe disease. The statements and conclusions in this document will therefore be updated as data become available.

Definitions

The following definitions and terminology are used by WHO throughout its policy recommendations on Covid-19 vaccination.

Booster doses are administered to a vaccinated population that has completed a primary vaccination series (currently one or two doses of vaccine depending on the product) when, with time, the immunity and clinical protection has fallen below a rate deemed sufficient in that population.

 

The objective of a booster dose is to restore vaccine effectiveness from that deemed no longer sufficient.

Additional doses of a vaccine may be needed as part of an extended primary series for target populations where the immune response rate following the standard primary series is deemed insufficient.

 

The objective of an additional dose in the primary series is to enhance the immune response to establish a sufficient level of effectiveness against disease.

 

In particular, immunocompromised individuals often fail to mount a protective immune response after a standard primary series, but also older adults may respond poorly to a standard primary series with some vaccines.

Global context

While many countries are far from reaching the 40 percentage coverage target, other countries have vaccinated well beyond this threshold, already reaching children and implementing extensive booster vaccination programmes.

 

At the time of release of this statement, globally about 20 percent of Covid-19 vaccine doses, daily, are used for booster or additional dose vaccination.

The primary global goal for the programme is to reduce deaths and severe disease due to Covid-19 and to protect the health system.

 

The level of population vaccination coverage needed to achieve this goal may differ between countries.

Subsequent public health goals include the reduction of Covid-19 disease burden and of viral transmission, to restore social and economic life, as described in WHO’s Strategy to Achieve Global Covid-19 vaccination by mid-2022.

Evidence of waning protection from primary vaccination series

The vast majority of current infections and Covid-19 cases are observed in unvaccinated people.

 

If breakthroughs occur in vaccinated persons, in most cases events are less severe than those in unvaccinated persons.

 

However, emerging data consistently show a decline in vaccine effectiveness against SARS-CoV2 infection and Covid-19 with time since vaccination, and more significant decline in older adults.

 

This evidence is mostly based on observational studies that may be subject to confounding factors.

Based on a recent systematic review and meta-regression analysis, vaccine effectiveness against severe Covid-19 decreased by about 8 percent (95 percent confidence interval) over a period of six months in all age groups.

In adults above 50 years, vaccine effectiveness against severe disease decreased by about 10 percent over the same period.

 

Vaccine effectiveness against symptomatic disease decreased by 32 percent for those above 50 years of age.

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 (ie 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.

Current situation in countries

At least 126 countries worldwide have already issued recommendations on booster or additional vaccination and more than 120 have started programmatic implementation.

 

Projections show that later this year global supply of vaccines will be sufficient for extensive use of boosters.

Optimisation of vaccine impact

In accordance with the Roadmap and WHO’s Strategy to Achieve Global Covid-19 Vaccination by mid-2022, the first priority of a vaccination programme is to reduce mortality and severe disease and to protect health systems.

 

The most important measure to achieve this goal is to maximise coverage among those most likely to become seriously ill and those most likely to become infected especially those who are critical for health system functioning.

 

In this context, priority should be given to the prevention of severe disease and sustaining health systems. — WHO.

Share This:

Sponsored Links

We value your opinion! Take a moment to complete our survey

This will close in 20 seconds