According to a government scientist advisor, four weeks is too long between Covid jabs.
People have shared tips online about locations that give second doses after a month.
Last weekend, walk-in vaccination centers opened across England.
Public Health England states that Pfizer jabs are safe to be administered after 21 days.
Professor Anthony Harnden, a government scientist advisor, says that for most people the "sweet spot", eight weeks is sufficient. Anything earlier will mean you aren't protected as long.
Professor Anthony Harnden serves on the Joint Committee on Vaccination and Immunisation and advises the government on vaccine rollout.
He said, "The data strongly suggests that the longer you leave the second dose, the better your long-term protection will be."
"There's a sweet spot around eight weeks, and we wouldn’t recommend anyone to have the second dose before that."
According to the NHS website second doses should be administered "usually" eight to twelve weeks after the first.
Professor Harnden said he understood the concern about jabs going stale: "We want vaccines to be in arms, and not in refrigerators."
It is still more effective to wait for the right amount of time before getting a second vaccine.
Professor Harnden's advice may not be appropriate for many people who posted online to claim they have had another jab prior to the suggested wait period.
Prof. Harnden believes that this could mean that the virus's effectiveness is lower for younger people. He also says that booster jabs may be needed later in life.
The booster program is currently being planned for more than 50s this winter.
Prof. Harnden says, "If it turns out that young people are at greater risk than six months after vaccination," then we will adjust the booster program accordingly.
"But it's not necessary to do that at this time."
Professor Harnden states that young people made sacrifices during the pandemic. He says it is now in their best interest to get vaccinated.
"We know they are highly effective. We know that there are some cases of Covid in young people, especially long-term Covid.
"There are many myths about the vaccine, especially those around fertility. These myths are totally false."
Prof. Harnden, if the health reasons aren’t enough to convince you: "We don’t know what other countries will do and we’re seeing more countries requiring vaccine passports.
"I believe that if you plan to travel in the future, you will need the vaccine."
He says that it is "highly probable" that a UK vaccine passport system will be introduced at some point. We will need to verify the status of people before we allow them in.
"And so, what I would tell young people is that if you receive an offer, take it."
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