COVID-19 patients only need one vaccine dose, but everyone may need future booster shots

LOS ANGELES, Calif. — Already had COVID-19? Researchers at UCLA have a bit of good news after your ordeal. A new study shows patients who recover from a coronavirus infection only need one vaccine dose to achieve full protection during the pandemic. Unfortunately, the results also show this immunity to COVID may not last forever and everyone may need booster shots in the future.

The study in the journal ACS Nano adds to previous research which finds COVID patients have already started building up an immune defense against the virus. In those reports, scientists discovered that coronavirus patients start producing their own antibodies to fight the infection and also create memory cells, which retain a record of old illnesses so the immune system knows how to fight them in the future.

Both the Pfizer-BioNTech and Moderna coronavirus vaccines have an effectiveness of about 95 percent. Both of these two-shot treatments use mRNA to trigger an immune response in the recipients. The immune system starts producing antibodies which target the SARS-CoV-2 spike protein receptor binding domain (RBD). This spike is what the virus uses to attach itself to human cells and infect the body.

For people who have not contracted COVID-19, two doses of these vaccines provide enough immunity to prevent symptoms from appearing. However, study authors say there have been few clinical trials so far involving the vaccines and people who recovered from COVID.

A second shot does nothing for COVID patients

Dr. Otto Yang and his team decided to compare antibody levels in people with and without a prior COVID infection and those receiving either one or two doses of the Pfizer or Moderna vaccines. Study authors started by examining 28 people who never contracted the virus. Results show one dose of either vaccine created antibody levels similar to those in COVID patients with a mild case of the virus. Their second dose however, created an antibody response closer to patients dealing with a severe case of the illness.

The team then tested 36 people who had a case of COVID-19 before their vaccinations. In those participants, one vaccine dose produced a response equal to that of a COVID patient with life-threatening symptoms. Moreover, a second vaccine dose did not provide any added protection against COVID-19.

How long will this protection last?

Study authors note the jury is still out on how long these vaccines will last as the pandemic continues. Their findings show antibody levels start to drop off after the second shot. After 85 days, vaccine recipients lose about 90 percent of the SARS-CoV-2 antibodies their immune system created. This doesn’t necessarily mean the COVID vaccines are only good for three months, but the team warns that future booster shots may be necessary whether you had COVID-19 or not.

Previous research suggests those who have dealt with a mild case of the virus could have protection from COVID for life. Although patients will lose most of their antibody-producing cells soon after vaccination, those studies show the human body keeps a small reserve in its bone marrow. These cells will sit there, ready to produce antibodies again if the virus returns.

The UCLA team believes scientists will need to run more tests on human T cells before they know for sure if the public will need a third round of COVID vaccinations.