Sir Keir Starmer has said laws may need to be brought in to challenge the spread of inaccurate theories on vaccines.
In an appearance on Good Morning Britain, the Labour leader said he would be prepared to support emergency legislation to tackle misinformation about vaccines.
Speaking via video link, he said: "We have to deal with anti-vax campaigns because they will cost lives.
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"If we need to pass emergency legislation to deal with them I would be willing to work with the Government on that."
Sir Keir said people needed to have confidence in getting vaccinated and that meant tackling misinformation.
He added: "That misinformation will cost lives. We need as many people vaccinated as possible, we need to give people confidence to get vaccinated.
"That's pulling together and it is also deal with this misinformation."
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His comments follow after the new Oxford/AstraZeneca vaccine began being rolled out by the NHS across the UK from January 4.
The "game changing" new jab was given the green light by the Medicines and Healthcare products Regulatory Agency (MHRA) last week, paving the way for the next stage of the phased vaccination programme.
The NHS will be the first health service in the world to deliver the life-saving jab, with hundreds of new vaccination sites to be set up this week, joining the 700 which are already in operation.
Unlike the Pfizer/BioNTech vaccine which has to be kept at minus 70 degrees until shortly before it is used, the new Oxford vaccine is easier to transport, making it easier to deliver in care homes.
On January 4, an 82-year-old man became the first person to get the vaccine.
