A World Health Organization panel said it's best to give people two doses of the same Covid-19 vaccine, but mixing and matching is a good solution for countries facing supply constraints.
"We still believe the best approach is to use the same vaccine for the two primary doses," said Alejandro Cravioto, chairman of the panel, at a briefing Thursday.
Vaccine combinations, already used by some governments, could help low- and middle-income countries manage stockpiles and deal with vaccine shortages as the new omicron variant spreads. European Union regulators endorsed mixing two different Covid-19 shots for initial vaccine schedules and boosters on Tuesday.
Cravioto said if countries mix vaccines, the best approach is to use a second dose of a messenger RNA or vector-based vaccine if the first dose was an inactivated vaccine. Messenger RNA vaccines are best followed by vector-based ones, he also said.
A study published by the University of Oxford earlier this week showed that mixing other vaccines with those from AstraZeneca Plc or Pfizer Inc. offered at least as effective protection against Covid as giving two doses of the same shots.
Separately, the WHO's Strategic Advisory Group of Experts on Immunization said that one dose of Johnson & Johnson's vaccine can be sufficient, though a second dose does increase protection.
The panel also repeated a call that countries should first fight vaccine inequity before giving boosters to the general population. The body recommends third doses for only specific situations including immunocompromised people, those over 60 and people who received inactivated vaccinations.
The panel is more confident in same-vaccine dosings because most inoculations so far have been that type, and hence the most data backs that approach, said Kate O'Brien, who heads the WHO's vaccination division. However, the panel is "pretty neutral" on the choice countries make between the two methods.
The panel needs more data to give any recommendations regarding the omicron variant, Cravioto said. "As with others we might end up with something not as dangerous as was thought in the beginning."
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