In one, researchers at Israel’s largest hospital observed what happened when more than 7,000 employees were vaccinated. Between the first and second doses of the Pfizer / BioNTech vaccine, infection rates plummeted. From the second to the fourth week after the first injection, rates of symptomatic infection fell by 85%.
In a second, Canadian researchers found evidence of more than 90% protection after a single dose of the Pfizer / BioNTech vaccine.
It is unclear how long this protection would last, and the Pfizer and Moderna vaccines were tested and authorized based on a two-dose regimen. Companies, the Food and Drug Administration and senior government officials, including the director of the National Institute of Allergy and Infectious Diseases, Dr. Anthony Fauci, have warned against what is known and tested.
“People need to keep getting their second chance,” Andy Slavitt, senior adviser to the White House on Covid-19’s response, told Chris Cuomo of CNN on Thursday night. “The second injection significantly increases their immunity, and what we have to do is to get over our first doses in the field more quickly, but no one is advising people to skip the second injection right now.”
But the United States is struggling to get even the first doses in the population and is seeing the number of deaths from the virus rising steadily to 500,000. Although US federal officials initially said they hoped anyone who wanted a vaccine could get it by April, they have now postponed that deadline to July.
And new variants that appear to make the virus more contagious are emerging around the world and across the country. It is possible that they could fuel a resurgence in the spread of the virus long before 70% to 85% of the population – the percentage that Fauci estimates is necessary to obtain collective immunity – can be vaccinated.
The team looked at the rate of infections for three weeks or more before workers received a second dose of the vaccine. They found a 47% reduction in symptomatic coronavirus infections among healthcare professionals during the first two weeks after the first injection, and an 85% reduction in the following two weeks.
“Our data show substantial initial reductions in SARS-CoV-2 infection and symptomatic COVID-19 rates after administration of the first dose of the vaccine,” wrote Dr. Eyal Leshem and colleagues.
“Early reductions in COVID-19 rates provide support for the postponement of the second dose in countries facing shortages of vaccines and scarce resources, to allow greater coverage of the population with a single dose.”
They examined the documents submitted by Pfizer and its partner BioNTech to the FDA when they sought an emergency use permit last year.
“Even before the second dose, BNT162b2 was highly effective, with a vaccine effectiveness of 92.6%, a finding similar to the effectiveness of the first 92.1% dose reported for the mRNA-1273 (Modern) vaccine,” they wrote.
“With this first highly protective dose, the benefits derived from a scarce supply of vaccine could be maximized by postponing second doses until all members of the priority group receive at least one dose,” they added.
They noted that it is unclear how long the protection will last if people receive only one dose of the vaccine. Clinical trials show a large increase in antibody production after the second dose of Moderna or Pfizer vaccine.
“Given the current shortage of vaccines, postponing the second dose is a national security issue that, if ignored, will certainly result in thousands of Covid-19 – hospitalizations and deaths related to this winter in the United States – hospitalizations and deaths that would have been avoided with the first dose of the vaccine “, they argued.
Dr. Tom Frieden, former director of the United States Centers for Disease Control and Prevention and now CEO of the health advocacy organization Resolve to Save Lives, says there are arguments for and against postponing the second dose until millions of people can be vaccinated.
“Subsequent doses ‘increase’ the immune response, activating immune cells created after the first dose to produce stronger and longer-lasting protection,” he added.
“For some COVID-19 vaccines, an important reason for multiple doses is to increase the strength of the antibody response.”
But he also notes that increasing the time between doses has never been shown to reduce the effectiveness of a vaccine and, in some cases – the HPV vaccine is an example – strengthens the immune response.
“However, a disadvantage of a longer interval between doses of any type of vaccine is that full protection is unlikely until all doses have been administered. In addition, for mRNA vaccines, such as the Pfizer and Modena vaccines, It is not yet known whether the timing of the second dose is critical for the production of a sustained immune response, because mRNA vaccines were not used in end-stage tests or approved for use before the COVID-19 pandemic, “noted Frieden .
The arrival of more communicable variants could change the equation, he said. “Maximizing the number of people with some level of immunity can be especially important if a highly transmissible variant is spreading rapidly. Some experts in the U.S. have suggested renewed consideration of a policy to delay second doses in favor of administering a first dose to more people, because highly transmissible SARS-CoV-2 variant strains are spreading across the United States. “
But there is another argument. What if the new variants spread among people who are only partially protected by having a dose of vaccine – and even worse variants evolve because of that?
“It is not clear how well a single dose of any two-dose COVID-19 vaccine can prevent infection with emerging variants,” noted Frieden.
Even single-dose vaccines do not resolve the dilemma completely. Johnson & Johnson is seeking FDA authorization for its single dose of Covid-19. But he is also testing a two-dose regimen to see if it works better.