Single Dose Vaccine?

The demand for coronavirus vaccine has exceeded the supply in many localities giving rise to suggestion that perhaps a single dose of either the Moderna or Pfizer vaccine would provide sufficient protection. The initial recommendation was to extend the interval between the first and second dose of the vaccines. For the Pfizer vaccine that interval was 3 weeks and for the Moderna vaccine the interval was 4 weeks. Now there are some who are suggesting that the second dose could be eliminated altogether. The thinking behind both possibilities is that it would double the number of vaccine immediately available to administer to Americans most in need of the vaccine. Many locales have held back a number of doses of vaccines for second doses rather than simply give out all the vaccine as initial doses. The Pfizer trial found 91% protection within 7 days of the first dose of the vaccine. The first dose of the Moderna vaccine provided 80% protection. Information from the ongoing Johnson & Johnson vaccine trial affirmed the scientific principle that immunity tends to increase in the second month after a vaccine with or without a second dose. A delayed second dose (such as 2-3 months) could possibly produce a better immune response. In the AstraZeneca/Oxford vaccine trials, the immune response was approximately 3X greater when the second dose was given at a 2-3 month interval versus a 4 week interval. Even partial immunity would reduce the severity of illness and certainly decrease the likelihood of death. Until greater supplies are available it seems reasonable to focus on administering at least one dose of vaccine to as many vulnerable individuals as possible.

A question has always been should those who have recovered from a Covid-19 infection receive the vaccine? Most believe the answer is yes because the immunity imparted by an active infection is believed to be short lived. Two small studies found that patients who recovered from Covid-19 infection who were given their first dose of vaccine exhibited a robust immune response that is usually seen after a second “booster” dose of vaccine. It appears in those previously infected with the virus the immune system is already “primed” and are able to produce antibodies at much higher levels than those who have had no experience with the virus. Based on their findings the study researchers believe that individuals who have had a previous Covid-19 infection do not require a second dose of the vaccine. Once again that could free up more doses of the vaccine for vulnerable individuals. “I do think that there is emerging evidence that someone with prior COVID infection may be able to achieve sufficient immunity with just a single dose of a two-dose vaccine regimen,” said Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security in Baltimore. Before the Food and Drug Administration (FDA) makes such recommendations more study would be required to show that a single shot in previously infected people would provide a sufficient boost to their immune memory. By that time we will hopefully have additional supplies of the current approved vaccines and others that are in phase 3 trials.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s