State health officials urge people to return for 2nd COVID shot

Some Arizonans getting the COVID-19 vaccine are not coming back for their second shot, which experts say is concerning because both doses are needed for full protection.

The Pfizer-BioNTech and Moderna vaccines are two-dose series and while a first dose will offer some protection, the vaccines are only considered fully effective with both shots.

The Johnson & Johnson vaccine requires just one dose but it’s a different type of vaccine that has been shown in clinical trials to provide adequate protection in one shot.

About 6% of those who have gotten the first dose of Pfizer or Moderna have not had their second dose recorded in Arizona’s vaccine management system within the recommended interval of six weeks, according to the state health department.

That’s about 93,000 people who did not show up for their second shot within six weeks of getting their first dose, said Steve Elliott, an Arizona Department of Health Services spokesperson.

Nationwide, more than 5 million people and close to 8% of those who got the first Pfizer or Moderna shot missed their second doses, the New York Times reported from Centers for Disease Control and Prevention data.

The reasons why may vary. Some may feel they’re protected enough with one shot; some may be scared off by reports of strong side effects following the second dose; others may have had side effects the first time around that they do not want to repeat; still, others may have had logistical or records issues.

“It is important to remember that at least for the two-dose vaccines, the Moderna vaccine and the Pfizer vaccine, a single dose is not sufficient to get full immunity,” said Dr. Joshua LaBaer, director of ASU’s Biodesign Institute, at a Wednesday news briefing.

“You really need that second dose. During that window between the two, there is still a risk of infection.”

CDC officials say that anyone who received the first dose of either the Moderna or Pfizer vaccines should get the second shot, even if they had side effects after the first shot, “unless a vaccination provider or your doctor tells you not to get it.”

For anyone still awaiting a second dose, the CDC has another important tip: Bring your vaccination card with you to your second shot appointment so your provider can fill in the information about your second dose.

Keep your vaccination card in case you need it for future use, CDC officials say, and consider taking a picture of it as a backup copy.

The Pfizer and Moderna vaccines’ efficacy has been studied as a twodose series.

“In their clinical trials and in developing those vaccines, they determined that one dose was not sufficient to get full immunity and that’s been borne out by studies that have looked at people and the infection rates that occur after a single dose and before the second dose,” LaBaer said.

One cannot compare and believe one dose of those vaccines is offering the same protection as the single-dose Johnson & Johnson vaccine, he said.

“The Johnson & Johnson vaccine is a different formulation, it’s a different delivery system, it’s an entirely different type of vaccine. For the two mRNA vaccines, it does not appear that a single dose is fully sufficient. To be fair, it does reduce infection rates, it does reduce severity rates in the population, but not to the level that you would expect to get from the second dose.”

The antibody response against the protein is much stronger after the second dose, and not as strong after the first dose, he said.

State health director Dr. Cara Christ said health officials want to make sure everyone is getting their second shot in order to get full protection, not just the partial protection offered by the first shot.

The good news is it seems people can get their second dose after the recommended three- or four-week interval and it’s still effective,” Christ said. “So if they missed their time, it’s not too late.”

The CDC recommends people get the second Pfizer shot 21 days after the first, or the second Moderna shot 28 days after the first.

The second dose can be given up to six weeks after the first if needed, the CDC says. And if it’s later than that, the series does not need to be restarted, although the agency says there is limited information on the effectiveness of getting the second shot later than six weeks.

“Even if it’s not within the three weeks or four weeks, or whatever the vaccine requires, even up to a couple of months later or even several months later, there’s still value in getting that second dose,” LaBaer said.

Christ said everyone who hasn’t gotten their second dose should get it.