While the latest data confirms lab and trial results of the safety and effectiveness of COVID-19 vaccines, the next hurdle in the vaccine race is understanding how different vaccines interact with each other.
If one brand is taken as the primary shot, can another brand be taken as a booster — if and when it is deemed necessary?
The question has significant implications not only for the already authorized vaccines, but also for shots coming down the pike. On Monday, Sanofi (SNY) and GlaxoSmithKline (GSK) announced positive phase 2 results and an imminent start to Phase 3 trials — with a focus on the global and booster markets for their vaccine, according to Sanofi's global medical head Su-Peing Ng.
"We are also looking at what role our vaccine could potentially play ... as a universal booster that will likely be needed," Ng told reporters Monday.
But the question about mixing vaccines has more immediate implications for childhood vaccines.
COVID-19 vaccines could soon be a new addition to the slew of annual vaccines for the school year for children, and one has already been approved for use in 12-15 year olds.
However, there is currently no data on co-administration of vaccines, according to CDC Director Dr. Rochelle Walensky.
"We still don't have any data as to whether you can give your Covid vaccine at the same time you give a measles vaccine or a tetanus vaccine or a Hepatitis B vaccine," she told Yahoo Finance Monday.
"We do have to be cautious of the overlapping side effects, and of the concern that if you get side effects from the Covid vaccine, somebody may attribute it to another vaccine," Walensky said.
The burden is currently on doctors to make the call as to whether to do so, but the CDC says the benefits outweigh the risks.
"[We are] operating with not a lot of data, but working really hard to make sure that our adolescents don't miss more vaccine," Walensky said.
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