Are you protected from measles? It may depend on your date of birth

Nearly two decades after measles was declared eliminated in the United States, the country and the world experienced a resurgence of cases, including adults who thought they were protected by the vaccine. Now some are wondering if they are properly vaccinated and still risk getting measles.

In a video posted on YouTube last week, a Detroit rabbi who said he had been "fully vaccinated" nevertheless contracted measles – "three brutal weeks," he said. In another recent case, an Israeli air hostess was unable to breathe alone after a terrible complication of measles: inflammation and swelling of the brain, called encephalitis. Health authorities believe that she also received a vaccine.

"It's so contagious. And the way people travel today does not require much, "said Dr. John Cullen, current president of the American Academy of Family Physicians and Family Physician in Valdez, Alaska.

"I have never seen cases of measles," he added. "But it's only a matter of time."

Adding to the uncertainty, some adults simply do not know their vaccination status or have long lost their documents, Cullen said. The history of measles vaccine has also raised questions about how people of different ages have been vaccinated: not only has the recommended number of doses changed over the years, but the vaccine itself has also exchange.

He recalled that several years ago, a case of measles appeared in Fairbanks, Alaska – the first case of this state in years. Worried to have been exposed and unsure as to whether they were properly vaccinated, patients to him who had gone there asked for a dose of the vaccine, just in case. (When it is administered within three days of exposure to the virus, the vaccine may offer some protection or mitigate the disease, according to health officials.)

Although Alaska has not seen a case this year, health officials have issued an alert following an emergency declaration in the neighboring state of Washington, which has confirmed dozens of cases. 2019.

"If we see a substantial increase in the number of measles infections, there will be many more people wondering about their immunization status," he said.

What are the current recommendations for measles vaccine?

Doctors recommend two doses of the MMR vaccine, so called because it covers measles, mumps and rubella. Doctors administer the first dose between 12 and 15 months, the second between 4 and 6 years.

The current recommendation was published in 1989 by the US Centers for Disease Control and Prevention. Previously, a single dose recommendation had been in place since 1963.

Before we received a vaccine, the agency announced that between 3 and 4 million Americans were infected each year, including 48,000 hospitalizations and 400 to 500 deaths.

In recent years, fewer than 100 cases have been reported throughout the country. But the virus has returned in the years to come, especially in 2019, largely thanks to anti-vaxers, according to experts.

"The reason we have hesitation to vaccinate in this country is that people do not remember how bad it was," Cullen said.

A dose of vaccine against two: what is the difference?

If you have been vaccinated with two doses, according to the latest 1989 guidelines, the CDC states that you have a 97% chance of being protected against measles. And if these last percent come into contact with the virus, they are less likely to pass it on to other people and their disease is often less serious.

One dose is still effective at around 93% to prevent the disease.

"Most virologists only dream of such an effective solution," Dr. Anne Schuchat, CDC's Senior Deputy Director, wrote in 2015 on today's measles vaccine.

The second dose, however, is not a reminder in itself. In research studies, almost everyone has developed signs of immunity against measles with a single dose – and the vast majority of the time, this immunity lasts a lifetime, experts said.

"It was in clinical trials where everything was very strictly managed," said Dr. William Schaffner, an infectious disease specialist at the Vanderbilt University School of Medicine and CDC adviser on vaccines.

But in the real world, despite significant gains against the virus, health experts still found measles outbreaks in children and adolescents who would have been vaccinated with one dose.

A second dose seems to be the case, but the question remains: why did the vaccine fail the first time?

"When this was examined in more detail, it was discovered that in the tumult of busy people [medical] In practice, the vaccine was not always treated optimally, "said Schaffner.

For example, if a doctor or nurse vaccinated several children in a row, they might have left the vaccine out of the fridge too long, which would have caused it to deteriorate. Even placing it in the door of a refrigerator, which is slightly warmer than the interior, may in some cases be enough to degrade the temperature-sensitive vaccine, he added.

It's less of a threat now that health care providers are better informed about how to handle the vaccine. In addition, we opted for single-dose vials rather than multi-dose vials that could have been left between each dose, Schaffner said.

Nevertheless, giving two doses has allowed health systems to "fill" a small percentage of children for whom the vaccine was not used for the first time.

"This is a wonderfully American solution: we will double the cost of the vaccination program to protect this small group of children from measles and its complications," said Schaffner. "This strategy has worked brilliantly and has been adopted in developing countries.

"And the only way to undermine the system is to not vaccinate the children."

What vaccine did I receive?

If you were born before the 1960s, you may have never been vaccinated against measles because it was assumed that you were exposed to the virus. In fact, the CDC states that most people born before 1957 do not need the vaccine because "before vaccines were available, almost everyone was infected with the measles, mumps and rubella virus during the 'childhood".

Then, in 1963, two types of measles vaccines were introduced: one was "killed" and the other "live attenuated". The difference is that the first inactivates the measles virus, while the other has a weakened form.

The killed vaccine, which was administered to about 600,000 to 900,000 people, was killed himself in 1967 "because it did not protect against measles infection," says the CDC. The agency also recommended that people who have received this vaccine, or who do not know which of the vaccines they have received in those years, will be vaccinated again.

The following year, in 1968, a new version of the live vaccine arrived on the market. He was as effective as his living predecessor, attenuated and even surer than the first, as he had been weakened further. It is still used today and has been available in combination with mumps and rubella vaccines since 1971.

Experts say that many middle-aged adults who were vaccinated at first do not know what vaccine they received. Whether one has received the "live" or "killed" vaccine was not always documented, Schaffner said – and these days, these decades-old records might be untraceable.

"At the time, the profession was not as nuanced about administering vaccines," he said.

In addition, neither the CDC nor any national organization has kept a vaccination record. The different states have vaccination records, but these did not arrive until later. For many Americans, "Existing records are those that you or your parents received when administering the vaccines and those listed in the medical record of the doctor or clinic where the vaccines were administered. According to the CDC, which recommends that people search for baby books, school records and previous employers who were able to collect such information, such as the military.

But many adults will not be lucky.

The old records "just do not exist anymore, the doctors have closed their practice, they have retired, they have moved out," Schaffner said. "It would be almost impossible to actually resuscitate these records."

What do the experts recommend?

If you have received two doses of MMR or if laboratory results have shown immunity or prior measles infection, the CDC tells you that everything is ready.

If you have received a documented dose of the live vaccine and you do not have a high risk of exposure, the agency responds that this is also adequate.

People at higher risk, who are recommended by the agency to take two doses, could work in the health sector, travel abroad or be more likely to be affected by an outbreak.

Some people can not get vaccinated at all or have to wait: for example, people with weakened immune systems and babies too young to respond to the vaccine.

Born before 1957 and does not work in the health sector? The CDC considers this "presumptive evidence" of your immunity against exposure to the virus in the pre-vaccine era.

But what happens if you do not have written documentation on the right vaccine? For those who are unsure, the CDC says that you can simply roll up your sleeve for one or two extra doses.

"The MMR vaccine is safe and it's not harmful to get another dose," the agency says.

Cullen, however, acknowledged that the number of people uncertain about their immunization status could be very high.

"If we had an epidemic in our area, would we have enough MMR to distribute to those affected?", He asked. "Probably not, in these circumstances. Unfortunately, this is a bit of the new reality we are facing. "

There is a blood test that doctors can use to check for immunity as well, but obtaining the results may take some time, he added.

For the general population, Schaffner stated that the blood test was "expensive, impractical and rarely produced an actionable result".

"The juice is not worth the pressure," he said. "The way to prevent these elderly people from contracting measles is to make sure all children are immunized."

This content has been republished with CNN's permission.