The Centers for Disease Control and Prevention is urging doctors to conserve shots of a kind of tetanus vaccine, as the agency braces for a potential shortage of those shots this year.

Doctors should switch from using the so-called Td vaccine – the immunization that protects against both tetanus and diphtheria infections – to giving the broader Tdap vaccine instead whenever possible, the CDC now says. In addition to tetanus and diphtheria, the Tdap vaccine also offers protection against pertussis, the infection also known as "whooping cough."

This year's shortage risk stems from a decision by nonprofit vaccinemaker MassBiologics to discontinue production of its Td vaccine, branded as TdVax. 

Supplies of the shot will likely run low as soon as this summer from the shot's distributor Grifols, the CDC told a panel of its vaccine advisers Wednesday. 

"It's available through June, through sometime in June, but it won't be available beyond that," said Jeanne Santoli of the CDC's Immunization Services Division.

Why did MassBiologics stop making TdVax?

Use of the Td vaccine has declined in recent decades, as more doctors have switched to stocking the newer but often pricier Tdap vaccines now on the market.

Sarah Wiley, a spokesperson for MassBiologics, said the "similar vaccines have led to a reduction in demand" for TdVax

Wiley said the decision to stop making the shots was unrelated to a previous disruption to TdVax supply through last year, after the company faced scrutiny from the Food and Drug Administration over some lots they had manufactured.

The shots are often given as a booster dose every 10 years, though doctors are recommended to give them earlier when treating severe or dirty wounds and burns that can let tetanus bacteria into the body.

Grifols had marketed TdVax as an alternative for doctors treating patients with wounds "when Tdap isn't necessary," saying the shot "delivers what your patients need, and nothing they don't."

Sanofi also historically made a version of the vaccine that had a higher dose to protect against diphtheria, alongside tetanus. The vaccine maker stopped making so-called DT shot in 2020 and used up its supply by the end of 2022, the CDC says.

What alternatives are available for tetanus shots?

Not everyone can get the Tdap vaccine as their booster shot for tetanus instead. The CDC says some people face a "very rare" risk of developing a type of brain damage called encephalopathy from the pertussis component of Tdap vaccines. 

People who have developed encephalopathy after getting vaccinated are recommended to avoid future pertussis shots, and have no other option to get a tetanus booster.

"The limited supply of Td vaccine needs to be preserved for those with a contraindication to receiving pertussis-containing vaccines," the agency says in its guidance.

Sanofi says it will ramp up its supply of Tenivac, the last remaining Td vaccine available to U.S. patients. However, the CDC says this will likely not be enough to avoid a "constrained" market for the tetanus and diphtheria-only shots.

A Sanofi spokesperson confirmed it was "taking steps to augment its available U.S. supply" of Td vaccine, but declined to offer specific supply figures. Ordering limits are being levied in both public and private sector orders to manage the supply gap, the CDC said.

"A supplier is discontinuing production of tetanus/diphtheria vaccine. Because of this, there may be more healthcare providers ordering Tenivac," the Sanofi spokesperson said.

What is tetanus?

Widely found in the soil, tetanus is caused by the bacteria Clostridium tetani. The bacteria's spores can be difficult to kill with heat and disinfectants.

One of the first signs of tetanus infection is often its "lockjaw" symptoms, as the muscles spasm and tighten painfully from the bacteria's toxins attacking the brain and nervous system. Survivors can take months to recover from the infections. 

Cases from tetanus have fallen to only a few dozen each year, thanks in part to vaccines driving down the once-high rates of the often-deadly infections in the early 20th century. 

Preliminary CDC data tallies just 15 cases in 2023 and 28 in 2022 reported from the infection.

The CDC estimates 92.7% of kindergarteners nationwide were vaccinated with one of the tetanus vaccines for the 2022 to 2023 school year. Among adults, around 64.2% in 2022 said they had gotten their Td or Tdap shots.

Alexander Tin

Alexander Tin is a digital reporter for CBS News based in the Washington, D.C. bureau. He covers the Biden administration's public health agencies, including the federal response to infectious disease outbreaks like COVID-19.

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