Covid booster shot to use different brands

THE DUTERTE administration is now considering “heterologous vaccination” for fully vaccinated individuals who are up for their third dose of Covid-19 vaccine to boost immunity.

Heterologous vaccination or mixing different vaccine brands would ensure the public’s immunity against the deadly coronavirus regardless of manufacturers’ supply, said Carlito Galvez Jr., in-charge of the government’s vaccine procurement program.

Galvez said they are awaiting recommendations from vaccine experts before giving the third dose specifically to healthcare workers, immunocompromised people or those having an impaired immune system, and the elderly.

He said the emergency use authorization issued to different Covid-19 vaccine brands must also be amended before giving the booster shot to the intended segment of the population.

Apart from heterologous vaccination, Galvez said one other government strategy is to vaccinate 90% of the student population and teaching personnel to gradually bring the country back to normalcy.

Galvez, who is also the National Task Force Against Covid-19 policies chief implementer, said that apart from economic revival, the government also focuses on pediatric vaccination, considering the psychological and emotional toll of the pandemic on the youth as a result of the nearly two years of lockdowns and restrictions.

Citing studies conducted by psychologists, Galvez noted a 300 to 400% increase in cases of depression and suicidal ideation among the younger population during the pandemic.

“Once the children are vaccinated against the coronavirus, the government could start easing the restrictions, allowing young people to go out, socialize, and play,” he said.

With the help of the local governments, Galvez said he is optimistic that pediatric vaccination will be completed by December this year.

The World Health Organization with support of the Strategic Advisory Group of Experts (SAGE) on Immunization and its Covid-19 Vaccines Working Group is reviewing the emerging evidence on the use of heterologous priming schedules.

WHO said the most common reason for considering a heterologous Covid-19 vaccine as second priming dose is lack of availability of the same vaccine in settings with limited vaccine supply or unpredictable supply. It said interchangeability of vaccine products would therefore allow for added programmatic flexibility.

“There are other reasons to investigate the utility of heterologous priming such as reducing reactogenicity, increasing immunogenicity and enhancing vaccine effectiveness. Heterologous priming should only be instituted if supportive evidence is available,” WHO said.

WHO said SAGE continuously reviews new data on heterologous priming vaccine schedules.  Guidance is available in some of the product specific interim recommendations (to date, for mRNA vaccines, i.e. BNT162b2 or mRNA-1273, and ChAdOx1-S or recombinant vaccines).

In general, for Covid-19 vaccines listed for emergency use by WHO with a 2-dose primary series schedule, WHO recommends that the same vaccine product should be used for both doses. If different Covid-19 vaccine products are inadvertently administered in the two doses, no additional doses of either vaccine are recommended.

At present, mix and match schedules constitute off-label use of respective vaccines and as such should only be used if benefits outweigh the risks such as in situations of interrupted vaccine supply.

Studies to date of immune responses after a first dose of ChAdOx1-S products followed by an mRNA vaccine (BNT162b2 or mRNA-1273) show higher neutralising antibody levels and higher T cell-mediated immune responses in comparison with two doses of ChAdOx1-S products and similar levels to those of two mRNA vaccines. The sequence of the first dose being ChAdOx1-S followed by the mRNA vaccine as second dose was more immunogenic than a first dose mRNA vaccine followed by ChAdOx1-S vaccine. 

While these studies are encouraging, they require cautious interpretation given the limited sample sizes and lack of follow up, especially related to safety data, and the uncertain relevance of immunological readouts in relation to clinical impact. The first results on short-term vaccine effectiveness (VE) against infection following a heterologous schedule have become available from Denmark showing an effectiveness of 88% (95% CI 83-92%) when combining the ChAdOx1 and an mRNA vaccine, similar to the VE of two doses of an mRNA vaccine, in a population-wide register-based study when the Alpha variant was dominant. More observational data on safety and effectiveness will be forthcoming. 

While there is currently no data for heterologous priming with other vaccine products, a large number of clinical studies of various vaccine combinations and schedules are currently on-going. SAGE will review these data as they become available and update the recommendations accordingly, according to WHO. (Mindanao Examiner)